--- name: "bpf-helpers" section: "7" platform: "linux" package: "man-pages" version: "6.19-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/bpf-helpers" --- # bpf-helpers(7) list of eBPF helper functions ## Name BPF-HELPERS - list of eBPF helper functions ## DESCRIPTION The extended Berkeley Packet Filter (eBPF) subsystem consists in programs written in a pseudo-assembly language, then attached to one of the several kernel hooks and run in reaction of specific events. This framework differs from the older, "classic" BPF (or "cBPF") in several aspects, one of them being the ability to call special functions (or "helpers") from within a program. These functions are restricted to a white-list of helpers defined in the kernel. These helpers are used by eBPF programs to interact with the system, or with the context in which they work. For instance, they can be used to print debugging messages, to get the time since the system was booted, to interact with eBPF maps, or to manipulate network packets. Since there are several eBPF program types, and that they do not run in the same context, each program type can only call a subset of those helpers. Due to eBPF conventions, a helper can not have more than five arguments. Internally, eBPF programs call directly into the compiled helper functions without requiring any foreign-function interface. As a result, calling helpers introduces no overhead, thus offering excellent performance. This document is an attempt to list and document the helpers available to eBPF developers. They are sorted by chronological order (the oldest helpers in the kernel at the top). ## HELPERS - **void \*bpf\_map\_lookup\_elem(struct bpf\_map \**map*, const void \**key*)** - **Description** Perform a lookup in *map* for an entry associated to *key*. - **Return** Map value associated to *key*, or **NULL** if no entry was found. - **long bpf\_map\_update\_elem(struct bpf\_map \**map*, const void \**key*, const void \**value*, u64 *flags*)** - **Description** Add or update the value of the entry associated to *key* in *map* with *value*. *flags* is one of: - **BPF\_NOEXIST** The entry for *key* must not exist in the map. - **BPF\_EXIST** The entry for *key* must already exist in the map. - **BPF\_ANY** No condition on the existence of the entry for *key*. Flag value **BPF\_NOEXIST** cannot be used for maps of types **BPF\_MAP\_TYPE\_ARRAY** or **BPF\_MAP\_TYPE\_PERCPU\_ARRAY** (all elements always exist), the helper would return an error. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_map\_delete\_elem(struct bpf\_map \**map*, const void \**key*)** - **Description** Delete entry with *key* from *map*. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_probe\_read(void \**dst*, u32 *size*, const void \**unsafe\_ptr*)** - **Description** For tracing programs, safely attempt to read *size* bytes from kernel space address *unsafe\_ptr* and store the data in *dst*. Generally, use **bpf\_probe\_read\_user**() or **bpf\_probe\_read\_kernel**() instead. - **Return** 0 on success, or a negative error in case of failure. - **u64 bpf\_ktime\_get\_ns(void)** - **Description** Return the time elapsed since system boot, in nanoseconds. Does not include time the system was suspended. See: **clock\_gettime**(**CLOCK\_MONOTONIC**) - **Return** Current *ktime*. - **long bpf\_trace\_printk(const char \**fmt*, u32 *fmt\_size*, ...)** - **Description** This helper is a "printk()-like" facility for debugging. It prints a message defined by format *fmt* (of size *fmt\_size*) to file */sys/kernel/tracing/trace* from TraceFS, if available. It can take up to three additional **u64** arguments (as an eBPF helpers, the total number of arguments is limited to five). Each time the helper is called, it appends a line to the trace. Lines are discarded while */sys/kernel/tracing/trace* is open, use */sys/kernel/tracing/trace\_pipe* to avoid this. The format of the trace is customizable, and the exact output one will get depends on the options set in */sys/kernel/tracing/trace\_options* (see also the *README* file under the same directory). However, it usually defaults to something like: ``` telnet-470 [001] .N.. 419421.045894: 0x00000001: ``` In the above: - • **telnet** is the name of the current task. - • **470** is the PID of the current task. - • **001** is the CPU number on which the task is running. - • In **.N..**, each character refers to a set of options (whether irqs are enabled, scheduling options, whether hard/softirqs are running, level of preempt\_disabled respectively). **N** means that **TIF\_NEED\_RESCHED** and **PREEMPT\_NEED\_RESCHED** are set. - • **419421.045894** is a timestamp. - • **0x00000001** is a fake value used by BPF for the instruction pointer register. - • **\** is the message formatted with *fmt*. The conversion specifiers supported by *fmt* are similar, but more limited than for printk(). They are **%d**, **%i**, **%u**, **%x**, **%ld**, **%li**, **%lu**, **%lx**, **%lld**, **%lli**, **%llu**, **%llx**, **%p**, **%s**. No modifier (size of field, padding with zeroes, etc.) is available, and the helper will return **-EINVAL** (but print nothing) if it encounters an unknown specifier. Also, note that **bpf\_trace\_printk**() is slow, and should only be used for debugging purposes. For this reason, a notice block (spanning several lines) is printed to kernel logs and states that the helper should not be used "for production use" the first time this helper is used (or more precisely, when **trace\_printk**() buffers are allocated). For passing values to user space, perf events should be preferred. - **Return** The number of bytes written to the buffer, or a negative error in case of failure. - **u32 bpf\_get\_prandom\_u32(void)** - **Description** Get a pseudo-random number. From a security point of view, this helper uses its own pseudo-random internal state, and cannot be used to infer the seed of other random functions in the kernel. However, it is essential to note that the generator used by the helper is not cryptographically secure. - **Return** A random 32-bit unsigned value. - **u32 bpf\_get\_smp\_processor\_id(void)** - **Description** Get the SMP (symmetric multiprocessing) processor id. Note that all programs run with migration disabled, which means that the SMP processor id is stable during all the execution of the program. - **Return** The SMP id of the processor running the program. - **long bpf\_skb\_store\_bytes(struct sk\_buff \**skb*, u32 *offset*, const void \**from*, u32 *len*, u64 *flags*)** - **Description** Store *len* bytes from address *from* into the packet associated to *skb*, at *offset*. The *flags* are a combination of the following values: - **BPF\_F\_RECOMPUTE\_CSUM** Automatically update *skb***-\>csum** after storing the bytes. - **BPF\_F\_INVALIDATE\_HASH** Set *skb***-\>hash**, *skb***-\>swhash** and *skb***-\>l4hash** to 0. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_l3\_csum\_replace(struct sk\_buff \**skb*, u32 *offset*, u64 *from*, u64 *to*, u64 *size*)** - **Description** Recompute the layer 3 (e.g. IP) checksum for the packet associated to *skb*. Computation is incremental, so the helper must know the former value of the header field that was modified (*from*), the new value of this field (*to*), and the number of bytes (2 or 4) for this field, stored in *size*. Alternatively, it is possible to store the difference between the previous and the new values of the header field in *to*, by setting *from* and *size* to 0. For both methods, *offset* indicates the location of the IP checksum within the packet. This helper works in combination with **bpf\_csum\_diff**(), which does not update the checksum in-place, but offers more flexibility and can handle sizes larger than 2 or 4 for the checksum to update. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_l4\_csum\_replace(struct sk\_buff \**skb*, u32 *offset*, u64 *from*, u64 *to*, u64 *flags*)** - **Description** Recompute the layer 4 (e.g. TCP, UDP or ICMP) checksum for the packet associated to *skb*. Computation is incremental, so the helper must know the former value of the header field that was modified (*from*), the new value of this field (*to*), and the number of bytes (2 or 4) for this field, stored on the lowest four bits of *flags*. Alternatively, it is possible to store the difference between the previous and the new values of the header field in *to*, by setting *from* and the four lowest bits of *flags* to 0. For both methods, *offset* indicates the location of the IP checksum within the packet. In addition to the size of the field, *flags* can be added (bitwise OR) actual flags. With **BPF\_F\_MARK\_MANGLED\_0**, a null checksum is left untouched (unless **BPF\_F\_MARK\_ENFORCE** is added as well), and for updates resulting in a null checksum the value is set to **CSUM\_MANGLED\_0** instead. Flag **BPF\_F\_PSEUDO\_HDR** indicates that the modified header field is part of the pseudo-header. Flag **BPF\_F\_IPV6** should be set for IPv6 packets. This helper works in combination with **bpf\_csum\_diff**(), which does not update the checksum in-place, but offers more flexibility and can handle sizes larger than 2 or 4 for the checksum to update. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_tail\_call(void \**ctx*, struct bpf\_map \**prog\_array\_map*, u32 *index*)** - **Description** This special helper is used to trigger a "tail call", or in other words, to jump into another eBPF program. The same stack frame is used (but values on stack and in registers for the caller are not accessible to the callee). This mechanism allows for program chaining, either for raising the maximum number of available eBPF instructions, or to execute given programs in conditional blocks. For security reasons, there is an upper limit to the number of successive tail calls that can be performed. Upon call of this helper, the program attempts to jump into a program referenced at index *index* in *prog\_array\_map*, a special map of type **BPF\_MAP\_TYPE\_PROG\_ARRAY**, and passes *ctx*, a pointer to the context. If the call succeeds, the kernel immediately runs the first instruction of the new program. This is not a function call, and it never returns to the previous program. If the call fails, then the helper has no effect, and the caller continues to run its subsequent instructions. A call can fail if the destination program for the jump does not exist (i.e. *index* is superior to the number of entries in *prog\_array\_map*), or if the maximum number of tail calls has been reached for this chain of programs. This limit is defined in the kernel by the macro **MAX\_TAIL\_CALL\_CNT** (not accessible to user space), which is currently set to 33. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_clone\_redirect(struct sk\_buff \**skb*, u32 *ifindex*, u64 *flags*)** - **Description** Clone and redirect the packet associated to *skb* to another net device of index *ifindex*. Both ingress and egress interfaces can be used for redirection. The **BPF\_F\_INGRESS** value in *flags* is used to make the distinction (ingress path is selected if the flag is present, egress path otherwise). This is the only flag supported for now. In comparison with **bpf\_redirect**() helper, **bpf\_clone\_redirect**() has the associated cost of duplicating the packet buffer, but this can be executed out of the eBPF program. Conversely, **bpf\_redirect**() is more efficient, but it is handled through an action code where the redirection happens only after the eBPF program has returned. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. Positive error indicates a potential drop or congestion in the target device. The particular positive error codes are not defined. - **u64 bpf\_get\_current\_pid\_tgid(void)** - **Description** Get the current pid and tgid. - **Return** A 64-bit integer containing the current tgid and pid, and created as such: *current\_task***-\>tgid \<\< 32 \|** *current\_task***-\>pid**. - **u64 bpf\_get\_current\_uid\_gid(void)** - **Description** Get the current uid and gid. - **Return** A 64-bit integer containing the current GID and UID, and created as such: *current\_gid* **\<\< 32 \|** *current\_uid*. - **long bpf\_get\_current\_comm(void \**buf*, u32 *size\_of\_buf*)** - **Description** Copy the **comm** attribute of the current task into *buf* of *size\_of\_buf*. The **comm** attribute contains the name of the executable (excluding the path) for the current task. The *size\_of\_buf* must be strictly positive. On success, the helper makes sure that the *buf* is NUL-terminated. On failure, it is filled with zeroes. - **Return** 0 on success, or a negative error in case of failure. - **u32 bpf\_get\_cgroup\_classid(struct sk\_buff \**skb*)** - **Description** Retrieve the classid for the current task, i.e. for the net\_cls cgroup to which *skb* belongs. This helper can be used on TC egress path, but not on ingress. The net\_cls cgroup provides an interface to tag network packets based on a user-provided identifier for all traffic coming from the tasks belonging to the related cgroup. See also the related kernel documentation, available from the Linux sources in file *Documentation/admin-guide/cgroup-v1/net\_cls.rst*. The Linux kernel has two versions for cgroups: there are cgroups v1 and cgroups v2. Both are available to users, who can use a mixture of them, but note that the net\_cls cgroup is for cgroup v1 only. This makes it incompatible with BPF programs run on cgroups, which is a cgroup-v2-only feature (a socket can only hold data for one version of cgroups at a time). This helper is only available is the kernel was compiled with the **CONFIG\_CGROUP\_NET\_CLASSID** configuration option set to "**y**" or to "**m**". - **Return** The classid, or 0 for the default unconfigured classid. - **long bpf\_skb\_vlan\_push(struct sk\_buff \**skb*, \_\_be16 *vlan\_proto*, u16 *vlan\_tci*)** - **Description** Push a *vlan\_tci* (VLAN tag control information) of protocol *vlan\_proto* to the packet associated to *skb*, then update the checksum. Note that if *vlan\_proto* is different from **ETH\_P\_8021Q** and **ETH\_P\_8021AD**, it is considered to be **ETH\_P\_8021Q**. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_skb\_vlan\_pop(struct sk\_buff \**skb*)** - **Description** Pop a VLAN header from the packet associated to *skb*. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_skb\_get\_tunnel\_key(struct sk\_buff \**skb*, struct bpf\_tunnel\_key \**key*, u32 *size*, u64 *flags*)** - **Description** Get tunnel metadata. This helper takes a pointer *key* to an empty **struct bpf\_tunnel\_key** of **size**, that will be filled with tunnel metadata for the packet associated to *skb*. The *flags* can be set to **BPF\_F\_TUNINFO\_IPV6**, which indicates that the tunnel is based on IPv6 protocol instead of IPv4. The **struct bpf\_tunnel\_key** is an object that generalizes the principal parameters used by various tunneling protocols into a single struct. This way, it can be used to easily make a decision based on the contents of the encapsulation header, "summarized" in this struct. In particular, it holds the IP address of the remote end (IPv4 or IPv6, depending on the case) in *key***-\>remote\_ipv4** or *key***-\>remote\_ipv6**. Also, this struct exposes the *key***-\>tunnel\_id**, which is generally mapped to a VNI (Virtual Network Identifier), making it programmable together with the **bpf\_skb\_set\_tunnel\_key**() helper. Let's imagine that the following code is part of a program attached to the TC ingress interface, on one end of a GRE tunnel, and is supposed to filter out all messages coming from remote ends with IPv4 address other than 10.0.0.1: ``` int ret; struct bpf_tunnel_key key = {}; ret = bpf_skb_get_tunnel_key(skb, &key, sizeof(key), 0); if (ret < 0) return TC_ACT_SHOT; // drop packet if (key.remote_ipv4 != 0x0a000001) return TC_ACT_SHOT; // drop packet return TC_ACT_OK; // accept packet ``` This interface can also be used with all encapsulation devices that can operate in "collect metadata" mode: instead of having one network device per specific configuration, the "collect metadata" mode only requires a single device where the configuration can be extracted from this helper. This can be used together with various tunnels such as VXLan, Geneve, GRE or IP in IP (IPIP). - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_skb\_set\_tunnel\_key(struct sk\_buff \**skb*, struct bpf\_tunnel\_key \**key*, u32 *size*, u64 *flags*)** - **Description** Populate tunnel metadata for packet associated to *skb.* The tunnel metadata is set to the contents of *key*, of *size*. The *flags* can be set to a combination of the following values: - **BPF\_F\_TUNINFO\_IPV6** Indicate that the tunnel is based on IPv6 protocol instead of IPv4. - **BPF\_F\_ZERO\_CSUM\_TX** For IPv4 packets, add a flag to tunnel metadata indicating that checksum computation should be skipped and checksum set to zeroes. - **BPF\_F\_DONT\_FRAGMENT** Add a flag to tunnel metadata indicating that the packet should not be fragmented. - **BPF\_F\_SEQ\_NUMBER** Add a flag to tunnel metadata indicating that a sequence number should be added to tunnel header before sending the packet. This flag was added for GRE encapsulation, but might be used with other protocols as well in the future. - **BPF\_F\_NO\_TUNNEL\_KEY** Add a flag to tunnel metadata indicating that no tunnel key should be set in the resulting tunnel header. Here is a typical usage on the transmit path: ``` struct bpf_tunnel_key key; populate key ... bpf_skb_set_tunnel_key(skb, &key, sizeof(key), 0); bpf_clone_redirect(skb, vxlan_dev_ifindex, 0); ``` See also the description of the **bpf\_skb\_get\_tunnel\_key**() helper for additional information. - **Return** 0 on success, or a negative error in case of failure. - **u64 bpf\_perf\_event\_read(struct bpf\_map \**map*, u64 *flags*)** - **Description** Read the value of a perf event counter. This helper relies on a *map* of type **BPF\_MAP\_TYPE\_PERF\_EVENT\_ARRAY**. The nature of the perf event counter is selected when *map* is updated with perf event file descriptors. The *map* is an array whose size is the number of available CPUs, and each cell contains a value relative to one CPU. The value to retrieve is indicated by *flags*, that contains the index of the CPU to look up, masked with **BPF\_F\_INDEX\_MASK**. Alternatively, *flags* can be set to **BPF\_F\_CURRENT\_CPU** to indicate that the value for the current CPU should be retrieved. Note that before Linux 4.13, only hardware perf event can be retrieved. Also, be aware that the newer helper **bpf\_perf\_event\_read\_value**() is recommended over **bpf\_perf\_event\_read**() in general. The latter has some ABI quirks where error and counter value are used as a return code (which is wrong to do since ranges may overlap). This issue is fixed with **bpf\_perf\_event\_read\_value**(), which at the same time provides more features over the **bpf\_perf\_event\_read**() interface. Please refer to the description of **bpf\_perf\_event\_read\_value**() for details. - **Return** The value of the perf event counter read from the map, or a negative error code in case of failure. - **long bpf\_redirect(u32 *ifindex*, u64 *flags*)** - **Description** Redirect the packet to another net device of index *ifindex*. This helper is somewhat similar to **bpf\_clone\_redirect**(), except that the packet is not cloned, which provides increased performance. Except for XDP, both ingress and egress interfaces can be used for redirection. The **BPF\_F\_INGRESS** value in *flags* is used to make the distinction (ingress path is selected if the flag is present, egress path otherwise). Currently, XDP only supports redirection to the egress interface, and accepts no flag at all. The same effect can also be attained with the more generic **bpf\_redirect\_map**(), which uses a BPF map to store the redirect target instead of providing it directly to the helper. - **Return** For XDP, the helper returns **XDP\_REDIRECT** on success or **XDP\_ABORTED** on error. For other program types, the values are **TC\_ACT\_REDIRECT** on success or **TC\_ACT\_SHOT** on error. - **u32 bpf\_get\_route\_realm(struct sk\_buff \**skb*)** - **Description** Retrieve the realm or the route, that is to say the **tclassid** field of the destination for the *skb*. The identifier retrieved is a user-provided tag, similar to the one used with the net\_cls cgroup (see description for **bpf\_get\_cgroup\_classid**() helper), but here this tag is held by a route (a destination entry), not by a task. Retrieving this identifier works with the clsact TC egress hook (see also **[tc-bpf(8)](/tc-bpf/8.md)**), or alternatively on conventional classful egress qdiscs, but not on TC ingress path. In case of clsact TC egress hook, this has the advantage that, internally, the destination entry has not been dropped yet in the transmit path. Therefore, the destination entry does not need to be artificially held via **netif\_keep\_dst**() for a classful qdisc until the *skb* is freed. This helper is available only if the kernel was compiled with **CONFIG\_IP\_ROUTE\_CLASSID** configuration option. - **Return** The realm of the route for the packet associated to *skb*, or 0 if none was found. - **long bpf\_perf\_event\_output(void \**ctx*, struct bpf\_map \**map*, u64 *flags*, void \**data*, u64 *size*)** - **Description** Write raw *data* blob into a special BPF perf event held by *map* of type **BPF\_MAP\_TYPE\_PERF\_EVENT\_ARRAY**. This perf event must have the following attributes: **PERF\_SAMPLE\_RAW** as **sample\_type**, **PERF\_TYPE\_SOFTWARE** as **type**, and **PERF\_COUNT\_SW\_BPF\_OUTPUT** as **config**. The *flags* are used to indicate the index in *map* for which the value must be put, masked with **BPF\_F\_INDEX\_MASK**. Alternatively, *flags* can be set to **BPF\_F\_CURRENT\_CPU** to indicate that the index of the current CPU core should be used. The value to write, of *size*, is passed through eBPF stack and pointed by *data*. The context of the program *ctx* needs also be passed to the helper. On user space, a program willing to read the values needs to call **perf\_event\_open**() on the perf event (either for one or for all CPUs) and to store the file descriptor into the *map*. This must be done before the eBPF program can send data into it. An example is available in file *samples/bpf/trace\_output\_user.c* in the Linux kernel source tree (the eBPF program counterpart is in *samples/bpf/trace\_output.bpf.c*). **bpf\_perf\_event\_output**() achieves better performance than **bpf\_trace\_printk**() for sharing data with user space, and is much better suitable for streaming data from eBPF programs. Note that this helper is not restricted to tracing use cases and can be used with programs attached to TC or XDP as well, where it allows for passing data to user space listeners. Data can be: - • Only custom structs, - • Only the packet payload, or - • A combination of both. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_skb\_load\_bytes(const void \**skb*, u32 *offset*, void \**to*, u32 *len*)** - **Description** This helper was provided as an easy way to load data from a packet. It can be used to load *len* bytes from *offset* from the packet associated to *skb*, into the buffer pointed by *to*. Since Linux 4.7, usage of this helper has mostly been replaced by "direct packet access", enabling packet data to be manipulated with *skb***-\>data** and *skb***-\>data\_end** pointing respectively to the first byte of packet data and to the byte after the last byte of packet data. However, it remains useful if one wishes to read large quantities of data at once from a packet into the eBPF stack. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_get\_stackid(void \**ctx*, struct bpf\_map \**map*, u64 *flags*)** - **Description** Walk a user or a kernel stack and return its id. To achieve this, the helper needs *ctx*, which is a pointer to the context on which the tracing program is executed, and a pointer to a *map* of type **BPF\_MAP\_TYPE\_STACK\_TRACE**. The last argument, *flags*, holds the number of stack frames to skip (from 0 to 255), masked with **BPF\_F\_SKIP\_FIELD\_MASK**. The next bits can be used to set a combination of the following flags: - **BPF\_F\_USER\_STACK** Collect a user space stack instead of a kernel stack. - **BPF\_F\_FAST\_STACK\_CMP** Compare stacks by hash only. - **BPF\_F\_REUSE\_STACKID** If two different stacks hash into the same *stackid*, discard the old one. The stack id retrieved is a 32 bit long integer handle which can be further combined with other data (including other stack ids) and used as a key into maps. This can be useful for generating a variety of graphs (such as flame graphs or off-cpu graphs). For walking a stack, this helper is an improvement over **bpf\_probe\_read**(), which can be used with unrolled loops but is not efficient and consumes a lot of eBPF instructions. Instead, **bpf\_get\_stackid**() can collect up to **PERF\_MAX\_STACK\_DEPTH** both kernel and user frames. Note that this limit can be controlled with the **sysctl** program, and that it should be manually increased in order to profile long user stacks (such as stacks for Java programs). To do so, use: ``` # sysctl kernel.perf_event_max_stack= ``` - **Return** The positive or null stack id on success, or a negative error in case of failure. - **s64 bpf\_csum\_diff(\_\_be32 \**from*, u32 *from\_size*, \_\_be32 \**to*, u32 *to\_size*, \_\_wsum *seed*)** - **Description** Compute a checksum difference, from the raw buffer pointed by *from*, of length *from\_size* (that must be a multiple of 4), towards the raw buffer pointed by *to*, of size *to\_size* (same remark). An optional *seed* can be added to the value (this can be cascaded, the seed may come from a previous call to the helper). This is flexible enough to be used in several ways: - • With *from\_size* == 0, *to\_size* \> 0 and *seed* set to checksum, it can be used when pushing new data. - • With *from\_size* \> 0, *to\_size* == 0 and *seed* set to checksum, it can be used when removing data from a packet. - • With *from\_size* \> 0, *to\_size* \> 0 and *seed* set to 0, it can be used to compute a diff. Note that *from\_size* and *to\_size* do not need to be equal. This helper can be used in combination with **bpf\_l3\_csum\_replace**() and **bpf\_l4\_csum\_replace**(), to which one can feed in the difference computed with **bpf\_csum\_diff**(). - **Return** The checksum result, or a negative error code in case of failure. - **long bpf\_skb\_get\_tunnel\_opt(struct sk\_buff \**skb*, void \**opt*, u32 *size*)** - **Description** Retrieve tunnel options metadata for the packet associated to *skb*, and store the raw tunnel option data to the buffer *opt* of *size*. This helper can be used with encapsulation devices that can operate in "collect metadata" mode (please refer to the related note in the description of **bpf\_skb\_get\_tunnel\_key**() for more details). A particular example where this can be used is in combination with the Geneve encapsulation protocol, where it allows for pushing (with **bpf\_skb\_get\_tunnel\_opt**() helper) and retrieving arbitrary TLVs (Type-Length-Value headers) from the eBPF program. This allows for full customization of these headers. - **Return** The size of the option data retrieved. - **long bpf\_skb\_set\_tunnel\_opt(struct sk\_buff \**skb*, void \**opt*, u32 *size*)** - **Description** Set tunnel options metadata for the packet associated to *skb* to the option data contained in the raw buffer *opt* of *size*. See also the description of the **bpf\_skb\_get\_tunnel\_opt**() helper for additional information. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_skb\_change\_proto(struct sk\_buff \**skb*, \_\_be16 *proto*, u64 *flags*)** - **Description** Change the protocol of the *skb* to *proto*. Currently supported are transition from IPv4 to IPv6, and from IPv6 to IPv4. The helper takes care of the groundwork for the transition, including resizing the socket buffer. The eBPF program is expected to fill the new headers, if any, via **skb\_store\_bytes**() and to recompute the checksums with **bpf\_l3\_csum\_replace**() and **bpf\_l4\_csum\_replace**(). The main case for this helper is to perform NAT64 operations out of an eBPF program. Internally, the GSO type is marked as dodgy so that headers are checked and segments are recalculated by the GSO/GRO engine. The size for GSO target is adapted as well. All values for *flags* are reserved for future usage, and must be left at zero. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_skb\_change\_type(struct sk\_buff \**skb*, u32 *type*)** - **Description** Change the packet type for the packet associated to *skb*. This comes down to setting *skb***-\>pkt\_type** to *type*, except the eBPF program does not have a write access to *skb***-\>pkt\_type** beside this helper. Using a helper here allows for graceful handling of errors. The major use case is to change incoming *skb\*s to* *\*\*PACKET\_HOST\** in a programmatic way instead of having to recirculate via **redirect**(..., **BPF\_F\_INGRESS**), for example. Note that *type* only allows certain values. At this time, they are: - **PACKET\_HOST** Packet is for us. - **PACKET\_BROADCAST** Send packet to all. - **PACKET\_MULTICAST** Send packet to group. - **PACKET\_OTHERHOST** Send packet to someone else. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_skb\_under\_cgroup(struct sk\_buff \**skb*, struct bpf\_map \**map*, u32 *index*)** - **Description** Check whether *skb* is a descendant of the cgroup2 held by *map* of type **BPF\_MAP\_TYPE\_CGROUP\_ARRAY**, at *index*. - **Return** The return value depends on the result of the test, and can be: - • 0, if the *skb* failed the cgroup2 descendant test. - • 1, if the *skb* succeeded the cgroup2 descendant test. - • A negative error code, if an error occurred. - **u32 bpf\_get\_hash\_recalc(struct sk\_buff \**skb*)** - **Description** Retrieve the hash of the packet, *skb***-\>hash**. If it is not set, in particular if the hash was cleared due to mangling, recompute this hash. Later accesses to the hash can be done directly with *skb***-\>hash**. Calling **bpf\_set\_hash\_invalid**(), changing a packet prototype with **bpf\_skb\_change\_proto**(), or calling **bpf\_skb\_store\_bytes**() with the **BPF\_F\_INVALIDATE\_HASH** are actions susceptible to clear the hash and to trigger a new computation for the next call to **bpf\_get\_hash\_recalc**(). - **Return** The 32-bit hash. - **u64 bpf\_get\_current\_task(void)** - **Description** Get the current task. - **Return** A pointer to the current task struct. - **long bpf\_probe\_write\_user(void \**dst*, const void \**src*, u32 *len*)** - **Description** Attempt in a safe way to write *len* bytes from the buffer *src* to *dst* in memory. It only works for threads that are in user context, and *dst* must be a valid user space address. This helper should not be used to implement any kind of security mechanism because of TOC-TOU attacks, but rather to debug, divert, and manipulate execution of semi-cooperative processes. Keep in mind that this feature is meant for experiments, and it has a risk of crashing the system and running programs. Therefore, when an eBPF program using this helper is attached, a warning including PID and process name is printed to kernel logs. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_current\_task\_under\_cgroup(struct bpf\_map \**map*, u32 *index*)** - **Description** Check whether the probe is being run is the context of a given subset of the cgroup2 hierarchy. The cgroup2 to test is held by *map* of type **BPF\_MAP\_TYPE\_CGROUP\_ARRAY**, at *index*. - **Return** The return value depends on the result of the test, and can be: - • 1, if current task belongs to the cgroup2. - • 0, if current task does not belong to the cgroup2. - • A negative error code, if an error occurred. - **long bpf\_skb\_change\_tail(struct sk\_buff \**skb*, u32 *len*, u64 *flags*)** - **Description** Resize (trim or grow) the packet associated to *skb* to the new *len*. The *flags* are reserved for future usage, and must be left at zero. The basic idea is that the helper performs the needed work to change the size of the packet, then the eBPF program rewrites the rest via helpers like **bpf\_skb\_store\_bytes**(), **bpf\_l3\_csum\_replace**(), **bpf\_l3\_csum\_replace**() and others. This helper is a slow path utility intended for replies with control messages. And because it is targeted for slow path, the helper itself can afford to be slow: it implicitly linearizes, unclones and drops offloads from the *skb*. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_skb\_pull\_data(struct sk\_buff \**skb*, u32 *len*)** - **Description** Pull in non-linear data in case the *skb* is non-linear and not all of *len* are part of the linear section. Make *len* bytes from *skb* readable and writable. If a zero value is passed for *len*, then all bytes in the linear part of *skb* will be made readable and writable. This helper is only needed for reading and writing with direct packet access. For direct packet access, testing that offsets to access are within packet boundaries (test on *skb***-\>data\_end**) is susceptible to fail if offsets are invalid, or if the requested data is in non-linear parts of the *skb*. On failure the program can just bail out, or in the case of a non-linear buffer, use a helper to make the data available. The **bpf\_skb\_load\_bytes**() helper is a first solution to access the data. Another one consists in using **bpf\_skb\_pull\_data** to pull in once the non-linear parts, then retesting and eventually access the data. At the same time, this also makes sure the *skb* is uncloned, which is a necessary condition for direct write. As this needs to be an invariant for the write part only, the verifier detects writes and adds a prologue that is calling **bpf\_skb\_pull\_data()** to effectively unclone the *skb* from the very beginning in case it is indeed cloned. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. - **s64 bpf\_csum\_update(struct sk\_buff \**skb*, \_\_wsum *csum*)** - **Description** Add the checksum *csum* into *skb***-\>csum** in case the driver has supplied a checksum for the entire packet into that field. Return an error otherwise. This helper is intended to be used in combination with **bpf\_csum\_diff**(), in particular when the checksum needs to be updated after data has been written into the packet through direct packet access. - **Return** The checksum on success, or a negative error code in case of failure. - **void bpf\_set\_hash\_invalid(struct sk\_buff \**skb*)** - **Description** Invalidate the current *skb***-\>hash**. It can be used after mangling on headers through direct packet access, in order to indicate that the hash is outdated and to trigger a recalculation the next time the kernel tries to access this hash or when the **bpf\_get\_hash\_recalc**() helper is called. - **Return** void. - **long bpf\_get\_numa\_node\_id(void)** - **Description** Return the id of the current NUMA node. The primary use case for this helper is the selection of sockets for the local NUMA node, when the program is attached to sockets using the **SO\_ATTACH\_REUSEPORT\_EBPF** option (see also **[socket(7)](/socket/7.md)**), but the helper is also available to other eBPF program types, similarly to **bpf\_get\_smp\_processor\_id**(). - **Return** The id of current NUMA node. - **long bpf\_skb\_change\_head(struct sk\_buff \**skb*, u32 *len*, u64 *flags*)** - **Description** Grows headroom of packet associated to *skb* and adjusts the offset of the MAC header accordingly, adding *len* bytes of space. It automatically extends and reallocates memory as required. This helper can be used on a layer 3 *skb* to push a MAC header for redirection into a layer 2 device. All values for *flags* are reserved for future usage, and must be left at zero. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_xdp\_adjust\_head(struct xdp\_buff \**xdp\_md*, int *delta*)** - **Description** Adjust (move) *xdp\_md***-\>data** by *delta* bytes. Note that it is possible to use a negative value for *delta*. This helper can be used to prepare the packet for pushing or popping headers. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_probe\_read\_str(void \**dst*, u32 *size*, const void \**unsafe\_ptr*)** - **Description** Copy a NUL terminated string from an unsafe kernel address *unsafe\_ptr* to *dst*. See **bpf\_probe\_read\_kernel\_str**() for more details. Generally, use **bpf\_probe\_read\_user\_str**() or **bpf\_probe\_read\_kernel\_str**() instead. - **Return** On success, the strictly positive length of the string, including the trailing NUL character. On error, a negative value. - **u64 bpf\_get\_socket\_cookie(struct sk\_buff \**skb*)** - **Description** If the **struct sk\_buff** pointed by *skb* has a known socket, retrieve the cookie (generated by the kernel) of this socket. If no cookie has been set yet, generate a new cookie. Once generated, the socket cookie remains stable for the life of the socket. This helper can be useful for monitoring per socket networking traffic statistics as it provides a global socket identifier that can be assumed unique. - **Return** A 8-byte long unique number on success, or 0 if the socket field is missing inside *skb*. - **u64 bpf\_get\_socket\_cookie(struct bpf\_sock\_addr \**ctx*)** - **Description** Equivalent to bpf\_get\_socket\_cookie() helper that accepts *skb*, but gets socket from **struct bpf\_sock\_addr** context. - **Return** A 8-byte long unique number. - **u64 bpf\_get\_socket\_cookie(struct bpf\_sock\_ops \**ctx*)** - **Description** Equivalent to **bpf\_get\_socket\_cookie**() helper that accepts *skb*, but gets socket from **struct bpf\_sock\_ops** context. - **Return** A 8-byte long unique number. - **u64 bpf\_get\_socket\_cookie(struct sock \**sk*)** - **Description** Equivalent to **bpf\_get\_socket\_cookie**() helper that accepts *sk*, but gets socket from a BTF **struct sock**. This helper also works for sleepable programs. - **Return** A 8-byte long unique number or 0 if *sk* is NULL. - **u32 bpf\_get\_socket\_uid(struct sk\_buff \**skb*)** - **Description** Get the owner UID of the socked associated to *skb*. - **Return** The owner UID of the socket associated to *skb*. If the socket is **NULL**, or if it is not a full socket (i.e. if it is a time-wait or a request socket instead), **overflowuid** value is returned (note that **overflowuid** might also be the actual UID value for the socket). - **long bpf\_set\_hash(struct sk\_buff \**skb*, u32 *hash*)** - **Description** Set the full hash for *skb* (set the field *skb***-\>hash**) to value *hash*. - **Return** 0 - **long bpf\_setsockopt(void \**bpf\_socket*, int *level*, int *optname*, void \**optval*, int *optlen*)** - **Description** Emulate a call to **setsockopt()** on the socket associated to *bpf\_socket*, which must be a full socket. The *level* at which the option resides and the name *optname* of the option must be specified, see **[setsockopt(2)](/setsockopt/2.md)** for more information. The option value of length *optlen* is pointed by *optval*. *bpf\_socket* should be one of the following: - • **struct bpf\_sock\_ops** for **BPF\_PROG\_TYPE\_SOCK\_OPS**. - • **struct bpf\_sock\_addr** for **BPF\_CGROUP\_INET4\_CONNECT**, **BPF\_CGROUP\_INET6\_CONNECT** and **BPF\_CGROUP\_UNIX\_CONNECT**. This helper actually implements a subset of **setsockopt()**. It supports the following *level*s: - • **SOL\_SOCKET**, which supports the following *optname*s: **SO\_RCVBUF**, **SO\_SNDBUF**, **SO\_MAX\_PACING\_RATE**, **SO\_PRIORITY**, **SO\_RCVLOWAT**, **SO\_MARK**, **SO\_BINDTODEVICE**, **SO\_KEEPALIVE**, **SO\_REUSEADDR**, **SO\_REUSEPORT**, **SO\_BINDTOIFINDEX**, **SO\_TXREHASH**. - • **IPPROTO\_TCP**, which supports the following *optname*s: **TCP\_CONGESTION**, **TCP\_BPF\_IW**, **TCP\_BPF\_SNDCWND\_CLAMP**, **TCP\_SAVE\_SYN**, **TCP\_KEEPIDLE**, **TCP\_KEEPINTVL**, **TCP\_KEEPCNT**, **TCP\_SYNCNT**, **TCP\_USER\_TIMEOUT**, **TCP\_NOTSENT\_LOWAT**, **TCP\_NODELAY**, **TCP\_MAXSEG**, **TCP\_WINDOW\_CLAMP**, **TCP\_THIN\_LINEAR\_TIMEOUTS**, **TCP\_BPF\_DELACK\_MAX**, **TCP\_BPF\_RTO\_MIN**, **TCP\_BPF\_SOCK\_OPS\_CB\_FLAGS**. - • **IPPROTO\_IP**, which supports *optname* **IP\_TOS**. - • **IPPROTO\_IPV6**, which supports the following *optname*s: **IPV6\_TCLASS**, **IPV6\_AUTOFLOWLABEL**. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_skb\_adjust\_room(struct sk\_buff \**skb*, s32 *len\_diff*, u32 *mode*, u64 *flags*)** - **Description** Grow or shrink the room for data in the packet associated to *skb* by *len\_diff*, and according to the selected *mode*. By default, the helper will reset any offloaded checksum indicator of the skb to CHECKSUM\_NONE. This can be avoided by the following flag: - • **BPF\_F\_ADJ\_ROOM\_NO\_CSUM\_RESET**: Do not reset offloaded checksum data of the skb to CHECKSUM\_NONE. There are two supported modes at this time: - • **BPF\_ADJ\_ROOM\_MAC**: Adjust room at the mac layer (room space is added or removed between the layer 2 and layer 3 headers). - • **BPF\_ADJ\_ROOM\_NET**: Adjust room at the network layer (room space is added or removed between the layer 3 and layer 4 headers). The following flags are supported at this time: - • **BPF\_F\_ADJ\_ROOM\_FIXED\_GSO**: Do not adjust gso\_size. Adjusting mss in this way is not allowed for datagrams. - • **BPF\_F\_ADJ\_ROOM\_ENCAP\_L3\_IPV4**, **BPF\_F\_ADJ\_ROOM\_ENCAP\_L3\_IPV6**: Any new space is reserved to hold a tunnel header. Configure skb offsets and other fields accordingly. - • **BPF\_F\_ADJ\_ROOM\_ENCAP\_L4\_GRE**, **BPF\_F\_ADJ\_ROOM\_ENCAP\_L4\_UDP**: Use with ENCAP\_L3 flags to further specify the tunnel type. - • **BPF\_F\_ADJ\_ROOM\_ENCAP\_L2**(*len*): Use with ENCAP\_L3/L4 flags to further specify the tunnel type; *len* is the length of the inner MAC header. - • **BPF\_F\_ADJ\_ROOM\_ENCAP\_L2\_ETH**: Use with BPF\_F\_ADJ\_ROOM\_ENCAP\_L2 flag to further specify the L2 type as Ethernet. - • **BPF\_F\_ADJ\_ROOM\_DECAP\_L3\_IPV4**, **BPF\_F\_ADJ\_ROOM\_DECAP\_L3\_IPV6**: Indicate the new IP header version after decapsulating the outer IP header. Used when the inner and outer IP versions are different. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_redirect\_map(struct bpf\_map \**map*, u64 *key*, u64 *flags*)** - **Description** Redirect the packet to the endpoint referenced by *map* at index *key*. Depending on its type, this *map* can contain references to net devices (for forwarding packets through other ports), or to CPUs (for redirecting XDP frames to another CPU; but this is only implemented for native XDP (with driver support) as of this writing). The lower two bits of *flags* are used as the return code if the map lookup fails. This is so that the return value can be one of the XDP program return codes up to **XDP\_TX**, as chosen by the caller. The higher bits of *flags* can be set to BPF\_F\_BROADCAST or BPF\_F\_EXCLUDE\_INGRESS as defined below. With BPF\_F\_BROADCAST the packet will be broadcasted to all the interfaces in the map, with BPF\_F\_EXCLUDE\_INGRESS the ingress interface will be excluded when do broadcasting. See also **bpf\_redirect**(), which only supports redirecting to an ifindex, but doesn't require a map to do so. - **Return** **XDP\_REDIRECT** on success, or the value of the two lower bits of the *flags* argument on error. - **long bpf\_sk\_redirect\_map(struct sk\_buff \**skb*, struct bpf\_map \**map*, u32 *key*, u64 *flags*)** - **Description** Redirect the packet to the socket referenced by *map* (of type **BPF\_MAP\_TYPE\_SOCKMAP**) at index *key*. Both ingress and egress interfaces can be used for redirection. The **BPF\_F\_INGRESS** value in *flags* is used to make the distinction (ingress path is selected if the flag is present, egress path otherwise). This is the only flag supported for now. - **Return** **SK\_PASS** on success, or **SK\_DROP** on error. - **long bpf\_sock\_map\_update(struct bpf\_sock\_ops \**skops*, struct bpf\_map \**map*, void \**key*, u64 *flags*)** - **Description** Add an entry to, or update a *map* referencing sockets. The *skops* is used as a new value for the entry associated to *key*. *flags* is one of: - **BPF\_NOEXIST** The entry for *key* must not exist in the map. - **BPF\_EXIST** The entry for *key* must already exist in the map. - **BPF\_ANY** No condition on the existence of the entry for *key*. If the *map* has eBPF programs (parser and verdict), those will be inherited by the socket being added. If the socket is already attached to eBPF programs, this results in an error. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_xdp\_adjust\_meta(struct xdp\_buff \**xdp\_md*, int *delta*)** - **Description** Adjust the address pointed by *xdp\_md***-\>data\_meta** by *delta* (which can be positive or negative). Note that this operation modifies the address stored in *xdp\_md***-\>data**, so the latter must be loaded only after the helper has been called. The use of *xdp\_md***-\>data\_meta** is optional and programs are not required to use it. The rationale is that when the packet is processed with XDP (e.g. as DoS filter), it is possible to push further meta data along with it before passing to the stack, and to give the guarantee that an ingress eBPF program attached as a TC classifier on the same device can pick this up for further post-processing. Since TC works with socket buffers, it remains possible to set from XDP the **mark** or **priority** pointers, or other pointers for the socket buffer. Having this scratch space generic and programmable allows for more flexibility as the user is free to store whatever meta data they need. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_perf\_event\_read\_value(struct bpf\_map \**map*, u64 *flags*, struct bpf\_perf\_event\_value \**buf*, u32 *buf\_size*)** - **Description** Read the value of a perf event counter, and store it into *buf* of size *buf\_size*. This helper relies on a *map* of type **BPF\_MAP\_TYPE\_PERF\_EVENT\_ARRAY**. The nature of the perf event counter is selected when *map* is updated with perf event file descriptors. The *map* is an array whose size is the number of available CPUs, and each cell contains a value relative to one CPU. The value to retrieve is indicated by *flags*, that contains the index of the CPU to look up, masked with **BPF\_F\_INDEX\_MASK**. Alternatively, *flags* can be set to **BPF\_F\_CURRENT\_CPU** to indicate that the value for the current CPU should be retrieved. This helper behaves in a way close to **bpf\_perf\_event\_read**() helper, save that instead of just returning the value observed, it fills the *buf* structure. This allows for additional data to be retrieved: in particular, the enabled and running times (in *buf***-\>enabled** and *buf***-\>running**, respectively) are copied. In general, **bpf\_perf\_event\_read\_value**() is recommended over **bpf\_perf\_event\_read**(), which has some ABI issues and provides fewer functionalities. These values are interesting, because hardware PMU (Performance Monitoring Unit) counters are limited resources. When there are more PMU based perf events opened than available counters, kernel will multiplex these events so each event gets certain percentage (but not all) of the PMU time. In case that multiplexing happens, the number of samples or counter value will not reflect the case compared to when no multiplexing occurs. This makes comparison between different runs difficult. Typically, the counter value should be normalized before comparing to other experiments. The usual normalization is done as follows. ``` normalized_counter = counter * t_enabled / t_running ``` Where t\_enabled is the time enabled for event and t\_running is the time running for event since last normalization. The enabled and running times are accumulated since the perf event open. To achieve scaling factor between two invocations of an eBPF program, users can use CPU id as the key (which is typical for perf array usage model) to remember the previous value and do the calculation inside the eBPF program. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_perf\_prog\_read\_value(struct bpf\_perf\_event\_data \**ctx*, struct bpf\_perf\_event\_value \**buf*, u32 *buf\_size*)** - **Description** For an eBPF program attached to a perf event, retrieve the value of the event counter associated to *ctx* and store it in the structure pointed by *buf* and of size *buf\_size*. Enabled and running times are also stored in the structure (see description of helper **bpf\_perf\_event\_read\_value**() for more details). - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_getsockopt(void \**bpf\_socket*, int *level*, int *optname*, void \**optval*, int *optlen*)** - **Description** Emulate a call to **getsockopt()** on the socket associated to *bpf\_socket*, which must be a full socket. The *level* at which the option resides and the name *optname* of the option must be specified, see **[getsockopt(2)](/getsockopt/2.md)** for more information. The retrieved value is stored in the structure pointed by *opval* and of length *optlen*. *bpf\_socket* should be one of the following: - • **struct bpf\_sock\_ops** for **BPF\_PROG\_TYPE\_SOCK\_OPS**. - • **struct bpf\_sock\_addr** for **BPF\_CGROUP\_INET4\_CONNECT**, **BPF\_CGROUP\_INET6\_CONNECT** and **BPF\_CGROUP\_UNIX\_CONNECT**. This helper actually implements a subset of **getsockopt()**. It supports the same set of *optname*s that is supported by the **bpf\_setsockopt**() helper. The exceptions are **TCP\_BPF\_\*** is **bpf\_setsockopt**() only and **TCP\_SAVED\_SYN** is **bpf\_getsockopt**() only. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_override\_return(struct pt\_regs \**regs*, u64 *rc*)** - **Description** Used for error injection, this helper uses kprobes to override the return value of the probed function, and to set it to *rc*. The first argument is the context *regs* on which the kprobe works. This helper works by setting the PC (program counter) to an override function which is run in place of the original probed function. This means the probed function is not run at all. The replacement function just returns with the required value. This helper has security implications, and thus is subject to restrictions. It is only available if the kernel was compiled with the **CONFIG\_BPF\_KPROBE\_OVERRIDE** configuration option, and in this case it only works on functions tagged with **ALLOW\_ERROR\_INJECTION** in the kernel code. - **Return** 0 - **long bpf\_sock\_ops\_cb\_flags\_set(struct bpf\_sock\_ops \**bpf\_sock*, int *argval*)** - **Description** Attempt to set the value of the **bpf\_sock\_ops\_cb\_flags** field for the full TCP socket associated to *bpf\_sock\_ops* to *argval*. The primary use of this field is to determine if there should be calls to eBPF programs of type **BPF\_PROG\_TYPE\_SOCK\_OPS** at various points in the TCP code. A program of the same type can change its value, per connection and as necessary, when the connection is established. This field is directly accessible for reading, but this helper must be used for updates in order to return an error if an eBPF program tries to set a callback that is not supported in the current kernel. *argval* is a flag array which can combine these flags: - • **BPF\_SOCK\_OPS\_RTO\_CB\_FLAG** (retransmission time out) - • **BPF\_SOCK\_OPS\_RETRANS\_CB\_FLAG** (retransmission) - • **BPF\_SOCK\_OPS\_STATE\_CB\_FLAG** (TCP state change) - • **BPF\_SOCK\_OPS\_RTT\_CB\_FLAG** (every RTT) Therefore, this function can be used to clear a callback flag by setting the appropriate bit to zero. e.g. to disable the RTO callback: - **bpf\_sock\_ops\_cb\_flags\_set(bpf\_sock,** **bpf\_sock-\>bpf\_sock\_ops\_cb\_flags & ~BPF\_SOCK\_OPS\_RTO\_CB\_FLAG)** Here are some examples of where one could call such eBPF program: - • When RTO fires. - • When a packet is retransmitted. - • When the connection terminates. - • When a packet is sent. - • When a packet is received. - **Return** Code **-EINVAL** if the socket is not a full TCP socket; otherwise, a positive number containing the bits that could not be set is returned (which comes down to 0 if all bits were set as required). - **long bpf\_msg\_redirect\_map(struct sk\_msg\_buff \**msg*, struct bpf\_map \**map*, u32 *key*, u64 *flags*)** - **Description** This helper is used in programs implementing policies at the socket level. If the message *msg* is allowed to pass (i.e. if the verdict eBPF program returns **SK\_PASS**), redirect it to the socket referenced by *map* (of type **BPF\_MAP\_TYPE\_SOCKMAP**) at index *key*. Both ingress and egress interfaces can be used for redirection. The **BPF\_F\_INGRESS** value in *flags* is used to make the distinction (ingress path is selected if the flag is present, egress path otherwise). This is the only flag supported for now. - **Return** **SK\_PASS** on success, or **SK\_DROP** on error. - **long bpf\_msg\_apply\_bytes(struct sk\_msg\_buff \**msg*, u32 *bytes*)** - **Description** For socket policies, apply the verdict of the eBPF program to the next *bytes* (number of bytes) of message *msg*. For example, this helper can be used in the following cases: - • A single **sendmsg**() or **sendfile**() system call contains multiple logical messages that the eBPF program is supposed to read and for which it should apply a verdict. - • An eBPF program only cares to read the first *bytes* of a *msg*. If the message has a large payload, then setting up and calling the eBPF program repeatedly for all bytes, even though the verdict is already known, would create unnecessary overhead. When called from within an eBPF program, the helper sets a counter internal to the BPF infrastructure, that is used to apply the last verdict to the next *bytes*. If *bytes* is smaller than the current data being processed from a **sendmsg**() or **sendfile**() system call, the first *bytes* will be sent and the eBPF program will be re-run with the pointer for start of data pointing to byte number *bytes* **+ 1**. If *bytes* is larger than the current data being processed, then the eBPF verdict will be applied to multiple **sendmsg**() or **sendfile**() calls until *bytes* are consumed. Note that if a socket closes with the internal counter holding a non-zero value, this is not a problem because data is not being buffered for *bytes* and is sent as it is received. - **Return** 0 - **long bpf\_msg\_cork\_bytes(struct sk\_msg\_buff \**msg*, u32 *bytes*)** - **Description** For socket policies, prevent the execution of the verdict eBPF program for message *msg* until *bytes* (byte number) have been accumulated. This can be used when one needs a specific number of bytes before a verdict can be assigned, even if the data spans multiple **sendmsg**() or **sendfile**() calls. The extreme case would be a user calling **sendmsg**() repeatedly with 1-byte long message segments. Obviously, this is bad for performance, but it is still valid. If the eBPF program needs *bytes* bytes to validate a header, this helper can be used to prevent the eBPF program to be called again until *bytes* have been accumulated. - **Return** 0 - **long bpf\_msg\_pull\_data(struct sk\_msg\_buff \**msg*, u32 *start*, u32 *end*, u64 *flags*)** - **Description** For socket policies, pull in non-linear data from user space for *msg* and set pointers *msg***-\>data** and *msg***-\>data\_end** to *start* and *end* bytes offsets into *msg*, respectively. If a program of type **BPF\_PROG\_TYPE\_SK\_MSG** is run on a *msg* it can only parse data that the (**data**, **data\_end**) pointers have already consumed. For **sendmsg**() hooks this is likely the first scatterlist element. But for calls relying on the **sendpage** handler (e.g. **sendfile**()) this will be the range (**0**, **0**) because the data is shared with user space and by default the objective is to avoid allowing user space to modify data while (or after) eBPF verdict is being decided. This helper can be used to pull in data and to set the start and end pointer to given values. Data will be copied if necessary (i.e. if data was not linear and if start and end pointers do not point to the same chunk). A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. All values for *flags* are reserved for future usage, and must be left at zero. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_bind(struct bpf\_sock\_addr \**ctx*, struct sockaddr \**addr*, int *addr\_len*)** - **Description** Bind the socket associated to *ctx* to the address pointed by *addr*, of length *addr\_len*. This allows for making outgoing connection from the desired IP address, which can be useful for example when all processes inside a cgroup should use one single IP address on a host that has multiple IP configured. This helper works for IPv4 and IPv6, TCP and UDP sockets. The domain (*addr***-\>sa\_family**) must be **AF\_INET** (or **AF\_INET6**). It's advised to pass zero port (**sin\_port** or **sin6\_port**) which triggers IP\_BIND\_ADDRESS\_NO\_PORT-like behavior and lets the kernel efficiently pick up an unused port as long as 4-tuple is unique. Passing non-zero port might lead to degraded performance. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_xdp\_adjust\_tail(struct xdp\_buff \**xdp\_md*, int *delta*)** - **Description** Adjust (move) *xdp\_md***-\>data\_end** by *delta* bytes. It is possible to both shrink and grow the packet tail. Shrink done via *delta* being a negative integer. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_skb\_get\_xfrm\_state(struct sk\_buff \**skb*, u32 *index*, struct bpf\_xfrm\_state \**xfrm\_state*, u32 *size*, u64 *flags*)** - **Description** Retrieve the XFRM state (IP transform framework, see also **[ip-xfrm(8)](/ip-xfrm/8.md)**) at *index* in XFRM "security path" for *skb*. The retrieved value is stored in the **struct bpf\_xfrm\_state** pointed by *xfrm\_state* and of length *size*. All values for *flags* are reserved for future usage, and must be left at zero. This helper is available only if the kernel was compiled with **CONFIG\_XFRM** configuration option. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_get\_stack(void \**ctx*, void \**buf*, u32 *size*, u64 *flags*)** - **Description** Return a user or a kernel stack in bpf program provided buffer. To achieve this, the helper needs *ctx*, which is a pointer to the context on which the tracing program is executed. To store the stacktrace, the bpf program provides *buf* with a nonnegative *size*. The last argument, *flags*, holds the number of stack frames to skip (from 0 to 255), masked with **BPF\_F\_SKIP\_FIELD\_MASK**. The next bits can be used to set the following flags: - **BPF\_F\_USER\_STACK** Collect a user space stack instead of a kernel stack. - **BPF\_F\_USER\_BUILD\_ID** Collect (build\_id, file\_offset) instead of ips for user stack, only valid if **BPF\_F\_USER\_STACK** is also specified. *file\_offset* is an offset relative to the beginning of the executable or shared object file backing the vma which the *ip* falls in. It is *not* an offset relative to that object's base address. Accordingly, it must be adjusted by adding (sh\_addr - sh\_offset), where sh\_{addr,offset} correspond to the executable section containing *file\_offset* in the object, for comparisons to symbols' st\_value to be valid. **bpf\_get\_stack**() can collect up to **PERF\_MAX\_STACK\_DEPTH** both kernel and user frames, subject to sufficient large buffer size. Note that this limit can be controlled with the **sysctl** program, and that it should be manually increased in order to profile long user stacks (such as stacks for Java programs). To do so, use: ``` # sysctl kernel.perf_event_max_stack= ``` - **Return** The non-negative copied *buf* length equal to or less than *size* on success, or a negative error in case of failure. - **long bpf\_skb\_load\_bytes\_relative(const void \**skb*, u32 *offset*, void \**to*, u32 *len*, u32 *start\_header*)** - **Description** This helper is similar to **bpf\_skb\_load\_bytes**() in that it provides an easy way to load *len* bytes from *offset* from the packet associated to *skb*, into the buffer pointed by *to*. The difference to **bpf\_skb\_load\_bytes**() is that a fifth argument *start\_header* exists in order to select a base offset to start from. *start\_header* can be one of: - **BPF\_HDR\_START\_MAC** Base offset to load data from is *skb*'s mac header. - **BPF\_HDR\_START\_NET** Base offset to load data from is *skb*'s network header. In general, "direct packet access" is the preferred method to access packet data, however, this helper is in particular useful in socket filters where *skb***-\>data** does not always point to the start of the mac header and where "direct packet access" is not available. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_fib\_lookup(void \**ctx*, struct bpf\_fib\_lookup \**params*, int *plen*, u32 *flags*)** - **Description** Do FIB lookup in kernel tables using parameters in *params*. If lookup is successful and result shows packet is to be forwarded, the neighbor tables are searched for the nexthop. If successful (ie., FIB lookup shows forwarding and nexthop is resolved), the nexthop address is returned in ipv4\_dst or ipv6\_dst based on family, smac is set to mac address of egress device, dmac is set to nexthop mac address, rt\_metric is set to metric from route (IPv4/IPv6 only), and ifindex is set to the device index of the nexthop from the FIB lookup. *plen* argument is the size of the passed in struct. *flags* argument can be a combination of one or more of the following values: - **BPF\_FIB\_LOOKUP\_DIRECT** Do a direct table lookup vs full lookup using FIB rules. - **BPF\_FIB\_LOOKUP\_TBID** Used with BPF\_FIB\_LOOKUP\_DIRECT. Use the routing table ID present in *params*-\>tbid for the fib lookup. - **BPF\_FIB\_LOOKUP\_OUTPUT** Perform lookup from an egress perspective (default is ingress). - **BPF\_FIB\_LOOKUP\_SKIP\_NEIGH** Skip the neighbour table lookup. *params*-\>dmac and *params*-\>smac will not be set as output. A common use case is to call **bpf\_redirect\_neigh**() after doing **bpf\_fib\_lookup**(). - **BPF\_FIB\_LOOKUP\_SRC** Derive and set source IP addr in *params*-\>ipv{4,6}\_src for the nexthop. If the src addr cannot be derived, **BPF\_FIB\_LKUP\_RET\_NO\_SRC\_ADDR** is returned. In this case, *params*-\>dmac and *params*-\>smac are not set either. - **BPF\_FIB\_LOOKUP\_MARK** Use the mark present in *params*-\>mark for the fib lookup. This option should not be used with BPF\_FIB\_LOOKUP\_DIRECT, as it only has meaning for full lookups. *ctx* is either **struct xdp\_md** for XDP programs or **struct sk\_buff** tc cls\_act programs. - **Return** - • \< 0 if any input argument is invalid - • 0 on success (packet is forwarded, nexthop neighbor exists) - • \> 0 one of **BPF\_FIB\_LKUP\_RET\_** codes explaining why the packet is not forwarded or needs assist from full stack If lookup fails with BPF\_FIB\_LKUP\_RET\_FRAG\_NEEDED, then the MTU was exceeded and output params-\>mtu\_result contains the MTU. - **long bpf\_sock\_hash\_update(struct bpf\_sock\_ops \**skops*, struct bpf\_map \**map*, void \**key*, u64 *flags*)** - **Description** Add an entry to, or update a sockhash *map* referencing sockets. The *skops* is used as a new value for the entry associated to *key*. *flags* is one of: - **BPF\_NOEXIST** The entry for *key* must not exist in the map. - **BPF\_EXIST** The entry for *key* must already exist in the map. - **BPF\_ANY** No condition on the existence of the entry for *key*. If the *map* has eBPF programs (parser and verdict), those will be inherited by the socket being added. If the socket is already attached to eBPF programs, this results in an error. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_msg\_redirect\_hash(struct sk\_msg\_buff \**msg*, struct bpf\_map \**map*, void \**key*, u64 *flags*)** - **Description** This helper is used in programs implementing policies at the socket level. If the message *msg* is allowed to pass (i.e. if the verdict eBPF program returns **SK\_PASS**), redirect it to the socket referenced by *map* (of type **BPF\_MAP\_TYPE\_SOCKHASH**) using hash *key*. Both ingress and egress interfaces can be used for redirection. The **BPF\_F\_INGRESS** value in *flags* is used to make the distinction (ingress path is selected if the flag is present, egress path otherwise). This is the only flag supported for now. - **Return** **SK\_PASS** on success, or **SK\_DROP** on error. - **long bpf\_sk\_redirect\_hash(struct sk\_buff \**skb*, struct bpf\_map \**map*, void \**key*, u64 *flags*)** - **Description** This helper is used in programs implementing policies at the skb socket level. If the sk\_buff *skb* is allowed to pass (i.e. if the verdict eBPF program returns **SK\_PASS**), redirect it to the socket referenced by *map* (of type **BPF\_MAP\_TYPE\_SOCKHASH**) using hash *key*. Both ingress and egress interfaces can be used for redirection. The **BPF\_F\_INGRESS** value in *flags* is used to make the distinction (ingress path is selected if the flag is present, egress otherwise). This is the only flag supported for now. - **Return** **SK\_PASS** on success, or **SK\_DROP** on error. - **long bpf\_lwt\_push\_encap(struct sk\_buff \**skb*, u32 *type*, void \**hdr*, u32 *len*)** - **Description** Encapsulate the packet associated to *skb* within a Layer 3 protocol header. This header is provided in the buffer at address *hdr*, with *len* its size in bytes. *type* indicates the protocol of the header and can be one of: - **BPF\_LWT\_ENCAP\_SEG6** IPv6 encapsulation with Segment Routing Header (**struct ipv6\_sr\_hdr**). *hdr* only contains the SRH, the IPv6 header is computed by the kernel. - **BPF\_LWT\_ENCAP\_SEG6\_INLINE** Only works if *skb* contains an IPv6 packet. Insert a Segment Routing Header (**struct ipv6\_sr\_hdr**) inside the IPv6 header. - **BPF\_LWT\_ENCAP\_IP** IP encapsulation (GRE/GUE/IPIP/etc). The outer header must be IPv4 or IPv6, followed by zero or more additional headers, up to **LWT\_BPF\_MAX\_HEADROOM** total bytes in all prepended headers. Please note that if **skb\_is\_gso**(*skb*) is true, no more than two headers can be prepended, and the inner header, if present, should be either GRE or UDP/GUE. **BPF\_LWT\_ENCAP\_SEG6**\* types can be called by BPF programs of type **BPF\_PROG\_TYPE\_LWT\_IN**; **BPF\_LWT\_ENCAP\_IP** type can be called by bpf programs of types **BPF\_PROG\_TYPE\_LWT\_IN** and **BPF\_PROG\_TYPE\_LWT\_XMIT**. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_lwt\_seg6\_store\_bytes(struct sk\_buff \**skb*, u32 *offset*, const void \**from*, u32 *len*)** - **Description** Store *len* bytes from address *from* into the packet associated to *skb*, at *offset*. Only the flags, tag and TLVs inside the outermost IPv6 Segment Routing Header can be modified through this helper. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_lwt\_seg6\_adjust\_srh(struct sk\_buff \**skb*, u32 *offset*, s32 *delta*)** - **Description** Adjust the size allocated to TLVs in the outermost IPv6 Segment Routing Header contained in the packet associated to *skb*, at position *offset* by *delta* bytes. Only offsets after the segments are accepted. *delta* can be as well positive (growing) as negative (shrinking). A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_lwt\_seg6\_action(struct sk\_buff \**skb*, u32 *action*, void \**param*, u32 *param\_len*)** - **Description** Apply an IPv6 Segment Routing action of type *action* to the packet associated to *skb*. Each action takes a parameter contained at address *param*, and of length *param\_len* bytes. *action* can be one of: - **SEG6\_LOCAL\_ACTION\_END\_X** End.X action: Endpoint with Layer-3 cross-connect. Type of *param*: **struct in6\_addr**. - **SEG6\_LOCAL\_ACTION\_END\_T** End.T action: Endpoint with specific IPv6 table lookup. Type of *param*: **int**. - **SEG6\_LOCAL\_ACTION\_END\_B6** End.B6 action: Endpoint bound to an SRv6 policy. Type of *param*: **struct ipv6\_sr\_hdr**. - **SEG6\_LOCAL\_ACTION\_END\_B6\_ENCAP** End.B6.Encap action: Endpoint bound to an SRv6 encapsulation policy. Type of *param*: **struct ipv6\_sr\_hdr**. A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_rc\_repeat(void \**ctx*)** - **Description** This helper is used in programs implementing IR decoding, to report a successfully decoded repeat key message. This delays the generation of a key up event for previously generated key down event. Some IR protocols like NEC have a special IR message for repeating last button, for when a button is held down. The *ctx* should point to the lirc sample as passed into the program. This helper is only available is the kernel was compiled with the **CONFIG\_BPF\_LIRC\_MODE2** configuration option set to "**y**". - **Return** 0 - **long bpf\_rc\_keydown(void \**ctx*, u32 *protocol*, u64 *scancode*, u32 *toggle*)** - **Description** This helper is used in programs implementing IR decoding, to report a successfully decoded key press with *scancode*, *toggle* value in the given *protocol*. The scancode will be translated to a keycode using the rc keymap, and reported as an input key down event. After a period a key up event is generated. This period can be extended by calling either **bpf\_rc\_keydown**() again with the same values, or calling **bpf\_rc\_repeat**(). Some protocols include a toggle bit, in case the button was released and pressed again between consecutive scancodes. The *ctx* should point to the lirc sample as passed into the program. The *protocol* is the decoded protocol number (see **enum rc\_proto** for some predefined values). This helper is only available is the kernel was compiled with the **CONFIG\_BPF\_LIRC\_MODE2** configuration option set to "**y**". - **Return** 0 - **u64 bpf\_skb\_cgroup\_id(struct sk\_buff \**skb*)** - **Description** Return the cgroup v2 id of the socket associated with the *skb*. This is roughly similar to the **bpf\_get\_cgroup\_classid**() helper for cgroup v1 by providing a tag resp. identifier that can be matched on or used for map lookups e.g. to implement policy. The cgroup v2 id of a given path in the hierarchy is exposed in user space through the f\_handle API in order to get to the same 64-bit id. This helper can be used on TC egress path, but not on ingress, and is available only if the kernel was compiled with the **CONFIG\_SOCK\_CGROUP\_DATA** configuration option. - **Return** The id is returned or 0 in case the id could not be retrieved. - **u64 bpf\_get\_current\_cgroup\_id(void)** - **Description** Get the current cgroup id based on the cgroup within which the current task is running. - **Return** A 64-bit integer containing the current cgroup id based on the cgroup within which the current task is running. - **void \*bpf\_get\_local\_storage(void \**map*, u64 *flags*)** - **Description** Get the pointer to the local storage area. The type and the size of the local storage is defined by the *map* argument. The *flags* meaning is specific for each map type, and has to be 0 for cgroup local storage. Depending on the BPF program type, a local storage area can be shared between multiple instances of the BPF program, running simultaneously. A user should care about the synchronization by himself. For example, by using the **BPF\_ATOMIC** instructions to alter the shared data. - **Return** A pointer to the local storage area. - **long bpf\_sk\_select\_reuseport(struct sk\_reuseport\_md \**reuse*, struct bpf\_map \**map*, void \**key*, u64 *flags*)** - **Description** Select a **SO\_REUSEPORT** socket from a **BPF\_MAP\_TYPE\_REUSEPORT\_SOCKARRAY** *map*. It checks the selected socket is matching the incoming request in the socket buffer. - **Return** 0 on success, or a negative error in case of failure. - **u64 bpf\_skb\_ancestor\_cgroup\_id(struct sk\_buff \**skb*, int *ancestor\_level*)** - **Description** Return id of cgroup v2 that is ancestor of cgroup associated with the *skb* at the *ancestor\_level*. The root cgroup is at *ancestor\_level* zero and each step down the hierarchy increments the level. If *ancestor\_level* == level of cgroup associated with *skb*, then return value will be same as that of **bpf\_skb\_cgroup\_id**(). The helper is useful to implement policies based on cgroups that are upper in hierarchy than immediate cgroup associated with *skb*. The format of returned id and helper limitations are same as in **bpf\_skb\_cgroup\_id**(). - **Return** The id is returned or 0 in case the id could not be retrieved. - **struct bpf\_sock \*bpf\_sk\_lookup\_tcp(void \**ctx*, struct bpf\_sock\_tuple \**tuple*, u32 *tuple\_size*, u64 *netns*, u64 *flags*)** - **Description** Look for TCP socket matching *tuple*, optionally in a child network namespace *netns*. The return value must be checked, and if non-**NULL**, released via **bpf\_sk\_release**(). The *ctx* should point to the context of the program, such as the skb or socket (depending on the hook in use). This is used to determine the base network namespace for the lookup. *tuple\_size* must be one of: - **sizeof(*tuple*-\>ipv4)** Look for an IPv4 socket. - **sizeof(*tuple*-\>ipv6)** Look for an IPv6 socket. If the *netns* is a negative signed 32-bit integer, then the socket lookup table in the netns associated with the *ctx* will be used. For the TC hooks, this is the netns of the device in the skb. For socket hooks, this is the netns of the socket. If *netns* is any other signed 32-bit value greater than or equal to zero then it specifies the ID of the netns relative to the netns associated with the *ctx*. *netns* values beyond the range of 32-bit integers are reserved for future use. All values for *flags* are reserved for future usage, and must be left at zero. This helper is available only if the kernel was compiled with **CONFIG\_NET** configuration option. - **Return** Pointer to **struct bpf\_sock**, or **NULL** in case of failure. For sockets with reuseport option, the **struct bpf\_sock** result is from *reuse***-\>socks**\[\] using the hash of the tuple. - **struct bpf\_sock \*bpf\_sk\_lookup\_udp(void \**ctx*, struct bpf\_sock\_tuple \**tuple*, u32 *tuple\_size*, u64 *netns*, u64 *flags*)** - **Description** Look for UDP socket matching *tuple*, optionally in a child network namespace *netns*. The return value must be checked, and if non-**NULL**, released via **bpf\_sk\_release**(). The *ctx* should point to the context of the program, such as the skb or socket (depending on the hook in use). This is used to determine the base network namespace for the lookup. *tuple\_size* must be one of: - **sizeof(*tuple*-\>ipv4)** Look for an IPv4 socket. - **sizeof(*tuple*-\>ipv6)** Look for an IPv6 socket. If the *netns* is a negative signed 32-bit integer, then the socket lookup table in the netns associated with the *ctx* will be used. For the TC hooks, this is the netns of the device in the skb. For socket hooks, this is the netns of the socket. If *netns* is any other signed 32-bit value greater than or equal to zero then it specifies the ID of the netns relative to the netns associated with the *ctx*. *netns* values beyond the range of 32-bit integers are reserved for future use. All values for *flags* are reserved for future usage, and must be left at zero. This helper is available only if the kernel was compiled with **CONFIG\_NET** configuration option. - **Return** Pointer to **struct bpf\_sock**, or **NULL** in case of failure. For sockets with reuseport option, the **struct bpf\_sock** result is from *reuse***-\>socks**\[\] using the hash of the tuple. - **long bpf\_sk\_release(void \**sock*)** - **Description** Release the reference held by *sock*. *sock* must be a non-**NULL** pointer that was returned from **bpf\_sk\_lookup\_xxx**(). - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_map\_push\_elem(struct bpf\_map \**map*, const void \**value*, u64 *flags*)** - **Description** Push an element *value* in *map*. *flags* is one of: - **BPF\_EXIST** If the queue/stack is full, the oldest element is removed to make room for this. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_map\_pop\_elem(struct bpf\_map \**map*, void \**value*)** - **Description** Pop an element from *map*. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_map\_peek\_elem(struct bpf\_map \**map*, void \**value*)** - **Description** Get an element from *map* without removing it. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_msg\_push\_data(struct sk\_msg\_buff \**msg*, u32 *start*, u32 *len*, u64 *flags*)** - **Description** For socket policies, insert *len* bytes into *msg* at offset *start*. If a program of type **BPF\_PROG\_TYPE\_SK\_MSG** is run on a *msg* it may want to insert metadata or options into the *msg*. This can later be read and used by any of the lower layer BPF hooks. This helper may fail if under memory pressure (a malloc fails) in these cases BPF programs will get an appropriate error and BPF programs will need to handle them. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_msg\_pop\_data(struct sk\_msg\_buff \**msg*, u32 *start*, u32 *len*, u64 *flags*)** - **Description** Will remove *len* bytes from a *msg* starting at byte *start*. This may result in **ENOMEM** errors under certain situations if an allocation and copy are required due to a full ring buffer. However, the helper will try to avoid doing the allocation if possible. Other errors can occur if input parameters are invalid either due to *start* byte not being valid part of *msg* payload and/or *pop* value being to large. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_rc\_pointer\_rel(void \**ctx*, s32 *rel\_x*, s32 *rel\_y*)** - **Description** This helper is used in programs implementing IR decoding, to report a successfully decoded pointer movement. The *ctx* should point to the lirc sample as passed into the program. This helper is only available is the kernel was compiled with the **CONFIG\_BPF\_LIRC\_MODE2** configuration option set to "**y**". - **Return** 0 - **long bpf\_spin\_lock(struct bpf\_spin\_lock \**lock*)** - **Description** Acquire a spinlock represented by the pointer *lock*, which is stored as part of a value of a map. Taking the lock allows to safely update the rest of the fields in that value. The spinlock can (and must) later be released with a call to **bpf\_spin\_unlock**(*lock*). Spinlocks in BPF programs come with a number of restrictions and constraints: - • **bpf\_spin\_lock** objects are only allowed inside maps of types **BPF\_MAP\_TYPE\_HASH** and **BPF\_MAP\_TYPE\_ARRAY** (this list could be extended in the future). - • BTF description of the map is mandatory. - • The BPF program can take ONE lock at a time, since taking two or more could cause dead locks. - • Only one **struct bpf\_spin\_lock** is allowed per map element. - • When the lock is taken, calls (either BPF to BPF or helpers) are not allowed. - • The **BPF\_LD\_ABS** and **BPF\_LD\_IND** instructions are not allowed inside a spinlock-ed region. - • The BPF program MUST call **bpf\_spin\_unlock**() to release the lock, on all execution paths, before it returns. - • The BPF program can access **struct bpf\_spin\_lock** only via the **bpf\_spin\_lock**() and **bpf\_spin\_unlock**() helpers. Loading or storing data into the **struct** **bpf\_spin\_lock** *lock***;** field of a map is not allowed. - • To use the **bpf\_spin\_lock**() helper, the BTF description of the map value must be a struct and have **struct** **bpf\_spin\_lock** *anyname***;** field at the top level. Nested lock inside another struct is not allowed. - • The **struct bpf\_spin\_lock** *lock* field in a map value must be aligned on a multiple of 4 bytes in that value. - • Syscall with command **BPF\_MAP\_LOOKUP\_ELEM** does not copy the **bpf\_spin\_lock** field to user space. - • Syscall with command **BPF\_MAP\_UPDATE\_ELEM**, or update from a BPF program, do not update the **bpf\_spin\_lock** field. - • **bpf\_spin\_lock** cannot be on the stack or inside a networking packet (it can only be inside of a map values). - • **bpf\_spin\_lock** is available to root only. - • Tracing programs and socket filter programs cannot use **bpf\_spin\_lock**() due to insufficient preemption checks (but this may change in the future). - • **bpf\_spin\_lock** is not allowed in inner maps of map-in-map. - **Return** 0 - **long bpf\_spin\_unlock(struct bpf\_spin\_lock \**lock*)** - **Description** Release the *lock* previously locked by a call to **bpf\_spin\_lock**(*lock*). - **Return** 0 - **struct bpf\_sock \*bpf\_sk\_fullsock(struct bpf\_sock \**sk*)** - **Description** This helper gets a **struct bpf\_sock** pointer such that all the fields in this **bpf\_sock** can be accessed. - **Return** A **struct bpf\_sock** pointer on success, or **NULL** in case of failure. - **struct bpf\_tcp\_sock \*bpf\_tcp\_sock(struct bpf\_sock \**sk*)** - **Description** This helper gets a **struct bpf\_tcp\_sock** pointer from a **struct bpf\_sock** pointer. - **Return** A **struct bpf\_tcp\_sock** pointer on success, or **NULL** in case of failure. - **long bpf\_skb\_ecn\_set\_ce(struct sk\_buff \**skb*)** - **Description** Set ECN (Explicit Congestion Notification) field of IP header to **CE** (Congestion Encountered) if current value is **ECT** (ECN Capable Transport). Otherwise, do nothing. Works with IPv6 and IPv4. - **Return** 1 if the **CE** flag is set (either by the current helper call or because it was already present), 0 if it is not set. - **struct bpf\_sock \*bpf\_get\_listener\_sock(struct bpf\_sock \**sk*)** - **Description** Return a **struct bpf\_sock** pointer in **TCP\_LISTEN** state. **bpf\_sk\_release**() is unnecessary and not allowed. - **Return** A **struct bpf\_sock** pointer on success, or **NULL** in case of failure. - **struct bpf\_sock \*bpf\_skc\_lookup\_tcp(void \**ctx*, struct bpf\_sock\_tuple \**tuple*, u32 *tuple\_size*, u64 *netns*, u64 *flags*)** - **Description** Look for TCP socket matching *tuple*, optionally in a child network namespace *netns*. The return value must be checked, and if non-**NULL**, released via **bpf\_sk\_release**(). This function is identical to **bpf\_sk\_lookup\_tcp**(), except that it also returns timewait or request sockets. Use **bpf\_sk\_fullsock**() or **bpf\_tcp\_sock**() to access the full structure. This helper is available only if the kernel was compiled with **CONFIG\_NET** configuration option. - **Return** Pointer to **struct bpf\_sock**, or **NULL** in case of failure. For sockets with reuseport option, the **struct bpf\_sock** result is from *reuse***-\>socks**\[\] using the hash of the tuple. - **long bpf\_tcp\_check\_syncookie(void \**sk*, void \**iph*, u32 *iph\_len*, struct tcphdr \**th*, u32 *th\_len*)** - **Description** Check whether *iph* and *th* contain a valid SYN cookie ACK for the listening socket in *sk*. *iph* points to the start of the IPv4 or IPv6 header, while *iph\_len* contains **sizeof**(**struct iphdr**) or **sizeof**(**struct ipv6hdr**). *th* points to the start of the TCP header, while *th\_len* contains the length of the TCP header (at least **sizeof**(**struct tcphdr**)). - **Return** 0 if *iph* and *th* are a valid SYN cookie ACK, or a negative error otherwise. - **long bpf\_sysctl\_get\_name(struct bpf\_sysctl \**ctx*, char \**buf*, size\_t *buf\_len*, u64 *flags*)** - **Description** Get name of sysctl in /proc/sys/ and copy it into provided by program buffer *buf* of size *buf\_len*. The buffer is always NUL terminated, unless it's zero-sized. If *flags* is zero, full name (e.g. "net/ipv4/tcp\_mem") is copied. Use **BPF\_F\_SYSCTL\_BASE\_NAME** flag to copy base name only (e.g. "tcp\_mem"). - **Return** Number of character copied (not including the trailing NUL). **-E2BIG** if the buffer wasn't big enough (*buf* will contain truncated name in this case). - **long bpf\_sysctl\_get\_current\_value(struct bpf\_sysctl \**ctx*, char \**buf*, size\_t *buf\_len*)** - **Description** Get current value of sysctl as it is presented in /proc/sys (incl. newline, etc), and copy it as a string into provided by program buffer *buf* of size *buf\_len*. The whole value is copied, no matter what file position user space issued e.g. sys\_read at. The buffer is always NUL terminated, unless it's zero-sized. - **Return** Number of character copied (not including the trailing NUL). **-E2BIG** if the buffer wasn't big enough (*buf* will contain truncated name in this case). **-EINVAL** if current value was unavailable, e.g. because sysctl is uninitialized and read returns -EIO for it. - **long bpf\_sysctl\_get\_new\_value(struct bpf\_sysctl \**ctx*, char \**buf*, size\_t *buf\_len*)** - **Description** Get new value being written by user space to sysctl (before the actual write happens) and copy it as a string into provided by program buffer *buf* of size *buf\_len*. User space may write new value at file position \> 0. The buffer is always NUL terminated, unless it's zero-sized. - **Return** Number of character copied (not including the trailing NUL). **-E2BIG** if the buffer wasn't big enough (*buf* will contain truncated name in this case). **-EINVAL** if sysctl is being read. - **long bpf\_sysctl\_set\_new\_value(struct bpf\_sysctl \**ctx*, const char \**buf*, size\_t *buf\_len*)** - **Description** Override new value being written by user space to sysctl with value provided by program in buffer *buf* of size *buf\_len*. *buf* should contain a string in same form as provided by user space on sysctl write. User space may write new value at file position \> 0. To override the whole sysctl value file position should be set to zero. - **Return** 0 on success. **-E2BIG** if the *buf\_len* is too big. **-EINVAL** if sysctl is being read. - **long bpf\_strtol(const char \**buf*, size\_t *buf\_len*, u64 *flags*, long \**res*)** - **Description** Convert the initial part of the string from buffer *buf* of size *buf\_len* to a long integer according to the given base and save the result in *res*. The string may begin with an arbitrary amount of white space (as determined by [**isspace**(3)](/isspace/3.md)) followed by a single optional '**-**' sign. Five least significant bits of *flags* encode base, other bits are currently unused. Base must be either 8, 10, 16 or 0 to detect it automatically similar to user space [**strtol**(3)](/strtol/3.md). - **Return** Number of characters consumed on success. Must be positive but no more than *buf\_len*. **-EINVAL** if no valid digits were found or unsupported base was provided. **-ERANGE** if resulting value was out of range. - **long bpf\_strtoul(const char \**buf*, size\_t *buf\_len*, u64 *flags*, unsigned long \**res*)** - **Description** Convert the initial part of the string from buffer *buf* of size *buf\_len* to an unsigned long integer according to the given base and save the result in *res*. The string may begin with an arbitrary amount of white space (as determined by [**isspace**(3)](/isspace/3.md)). Five least significant bits of *flags* encode base, other bits are currently unused. Base must be either 8, 10, 16 or 0 to detect it automatically similar to user space [**strtoul**(3)](/strtoul/3.md). - **Return** Number of characters consumed on success. Must be positive but no more than *buf\_len*. **-EINVAL** if no valid digits were found or unsupported base was provided. **-ERANGE** if resulting value was out of range. - **void \*bpf\_sk\_storage\_get(struct bpf\_map \**map*, void \**sk*, void \**value*, u64 *flags*)** - **Description** Get a bpf-local-storage from a *sk*. Logically, it could be thought of getting the value from a *map* with *sk* as the **key**. From this perspective, the usage is not much different from **bpf\_map\_lookup\_elem**(*map*, **&***sk*) except this helper enforces the key must be a full socket and the map must be a **BPF\_MAP\_TYPE\_SK\_STORAGE** also. Underneath, the value is stored locally at *sk* instead of the *map*. The *map* is used as the bpf-local-storage "type". The bpf-local-storage "type" (i.e. the *map*) is searched against all bpf-local-storages residing at *sk*. *sk* is a kernel **struct sock** pointer for LSM program. *sk* is a **struct bpf\_sock** pointer for other program types. An optional *flags* (**BPF\_SK\_STORAGE\_GET\_F\_CREATE**) can be used such that a new bpf-local-storage will be created if one does not exist. *value* can be used together with **BPF\_SK\_STORAGE\_GET\_F\_CREATE** to specify the initial value of a bpf-local-storage. If *value* is **NULL**, the new bpf-local-storage will be zero initialized. - **Return** A bpf-local-storage pointer is returned on success. **NULL** if not found or there was an error in adding a new bpf-local-storage. - **long bpf\_sk\_storage\_delete(struct bpf\_map \**map*, void \**sk*)** - **Description** Delete a bpf-local-storage from a *sk*. - **Return** 0 on success. **-ENOENT** if the bpf-local-storage cannot be found. **-EINVAL** if sk is not a fullsock (e.g. a request\_sock). - **long bpf\_send\_signal(u32 *sig*)** - **Description** Send signal *sig* to the process of the current task. The signal may be delivered to any of this process's threads. - **Return** 0 on success or successfully queued. **-EBUSY** if work queue under nmi is full. **-EINVAL** if *sig* is invalid. **-EPERM** if no permission to send the *sig*. **-EAGAIN** if bpf program can try again. - **s64 bpf\_tcp\_gen\_syncookie(void \**sk*, void \**iph*, u32 *iph\_len*, struct tcphdr \**th*, u32 *th\_len*)** - **Description** Try to issue a SYN cookie for the packet with corresponding IP/TCP headers, *iph* and *th*, on the listening socket in *sk*. *iph* points to the start of the IPv4 or IPv6 header, while *iph\_len* contains **sizeof**(**struct iphdr**) or **sizeof**(**struct ipv6hdr**). *th* points to the start of the TCP header, while *th\_len* contains the length of the TCP header with options (at least **sizeof**(**struct tcphdr**)). - **Return** On success, lower 32 bits hold the generated SYN cookie in followed by 16 bits which hold the MSS value for that cookie, and the top 16 bits are unused. On failure, the returned value is one of the following: **-EINVAL** SYN cookie cannot be issued due to error **-ENOENT** SYN cookie should not be issued (no SYN flood) **-EOPNOTSUPP** kernel configuration does not enable SYN cookies **-EPROTONOSUPPORT** IP packet version is not 4 or 6 - **long bpf\_skb\_output(void \**ctx*, struct bpf\_map \**map*, u64 *flags*, void \**data*, u64 *size*)** - **Description** Write raw *data* blob into a special BPF perf event held by *map* of type **BPF\_MAP\_TYPE\_PERF\_EVENT\_ARRAY**. This perf event must have the following attributes: **PERF\_SAMPLE\_RAW** as **sample\_type**, **PERF\_TYPE\_SOFTWARE** as **type**, and **PERF\_COUNT\_SW\_BPF\_OUTPUT** as **config**. The *flags* are used to indicate the index in *map* for which the value must be put, masked with **BPF\_F\_INDEX\_MASK**. Alternatively, *flags* can be set to **BPF\_F\_CURRENT\_CPU** to indicate that the index of the current CPU core should be used. The value to write, of *size*, is passed through eBPF stack and pointed by *data*. *ctx* is a pointer to in-kernel struct sk\_buff. This helper is similar to **bpf\_perf\_event\_output**() but restricted to raw\_tracepoint bpf programs. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_probe\_read\_user(void \**dst*, u32 *size*, const void \**unsafe\_ptr*)** - **Description** Safely attempt to read *size* bytes from user space address *unsafe\_ptr* and store the data in *dst*. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_probe\_read\_kernel(void \**dst*, u32 *size*, const void \**unsafe\_ptr*)** - **Description** Safely attempt to read *size* bytes from kernel space address *unsafe\_ptr* and store the data in *dst*. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_probe\_read\_user\_str(void \**dst*, u32 *size*, const void \**unsafe\_ptr*)** - **Description** Copy a NUL terminated string from an unsafe user address *unsafe\_ptr* to *dst*. The *size* should include the terminating NUL byte. In case the string length is smaller than *size*, the target is not padded with further NUL bytes. If the string length is larger than *size*, just *size*-1 bytes are copied and the last byte is set to NUL. On success, returns the number of bytes that were written, including the terminal NUL. This makes this helper useful in tracing programs for reading strings, and more importantly to get its length at runtime. See the following snippet: ``` SEC("kprobe/sys_open") void bpf_sys_open(struct pt_regs *ctx) { char buf[PATHLEN]; // PATHLEN is defined to 256 int res = bpf_probe_read_user_str(buf, sizeof(buf), ctx->di); // Consume buf, for example push it to // userspace via bpf_perf_event_output(); we // can use res (the string length) as event // size, after checking its boundaries. } ``` In comparison, using **bpf\_probe\_read\_user**() helper here instead to read the string would require to estimate the length at compile time, and would often result in copying more memory than necessary. Another useful use case is when parsing individual process arguments or individual environment variables navigating *current***-\>mm-\>arg\_start** and *current***-\>mm-\>env\_start**: using this helper and the return value, one can quickly iterate at the right offset of the memory area. - **Return** On success, the strictly positive length of the output string, including the trailing NUL character. On error, a negative value. - **long bpf\_probe\_read\_kernel\_str(void \**dst*, u32 *size*, const void \**unsafe\_ptr*)** - **Description** Copy a NUL terminated string from an unsafe kernel address *unsafe\_ptr* to *dst*. Same semantics as with **bpf\_probe\_read\_user\_str**() apply. - **Return** On success, the strictly positive length of the string, including the trailing NUL character. On error, a negative value. - **long bpf\_tcp\_send\_ack(void \**tp*, u32 *rcv\_nxt*)** - **Description** Send out a tcp-ack. *tp* is the in-kernel struct **tcp\_sock**. *rcv\_nxt* is the ack\_seq to be sent out. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_send\_signal\_thread(u32 *sig*)** - **Description** Send signal *sig* to the thread corresponding to the current task. - **Return** 0 on success or successfully queued. **-EBUSY** if work queue under nmi is full. **-EINVAL** if *sig* is invalid. **-EPERM** if no permission to send the *sig*. **-EAGAIN** if bpf program can try again. - **u64 bpf\_jiffies64(void)** - **Description** Obtain the 64bit jiffies - **Return** The 64 bit jiffies - **long bpf\_read\_branch\_records(struct bpf\_perf\_event\_data \**ctx*, void \**buf*, u32 *size*, u64 *flags*)** - **Description** For an eBPF program attached to a perf event, retrieve the branch records (**struct perf\_branch\_entry**) associated to *ctx* and store it in the buffer pointed by *buf* up to size *size* bytes. - **Return** On success, number of bytes written to *buf*. On error, a negative value. The *flags* can be set to **BPF\_F\_GET\_BRANCH\_RECORDS\_SIZE** to instead return the number of bytes required to store all the branch entries. If this flag is set, *buf* may be NULL. **-EINVAL** if arguments invalid or **size** not a multiple of **sizeof**(**struct perf\_branch\_entry**). **-ENOENT** if architecture does not support branch records. - **long bpf\_get\_ns\_current\_pid\_tgid(u64 *dev*, u64 *ino*, struct bpf\_pidns\_info \**nsdata*, u32 *size*)** - **Description** Returns 0 on success, values for *pid* and *tgid* as seen from the current *namespace* will be returned in *nsdata*. - **Return** 0 on success, or one of the following in case of failure: **-EINVAL** if dev and inum supplied don't match dev\_t and inode number with nsfs of current task, or if dev conversion to dev\_t lost high bits. **-ENOENT** if pidns does not exists for the current task. - **long bpf\_xdp\_output(void \**ctx*, struct bpf\_map \**map*, u64 *flags*, void \**data*, u64 *size*)** - **Description** Write raw *data* blob into a special BPF perf event held by *map* of type **BPF\_MAP\_TYPE\_PERF\_EVENT\_ARRAY**. This perf event must have the following attributes: **PERF\_SAMPLE\_RAW** as **sample\_type**, **PERF\_TYPE\_SOFTWARE** as **type**, and **PERF\_COUNT\_SW\_BPF\_OUTPUT** as **config**. The *flags* are used to indicate the index in *map* for which the value must be put, masked with **BPF\_F\_INDEX\_MASK**. Alternatively, *flags* can be set to **BPF\_F\_CURRENT\_CPU** to indicate that the index of the current CPU core should be used. The value to write, of *size*, is passed through eBPF stack and pointed by *data*. *ctx* is a pointer to in-kernel struct xdp\_buff. This helper is similar to **bpf\_perf\_eventoutput**() but restricted to raw\_tracepoint bpf programs. - **Return** 0 on success, or a negative error in case of failure. - **u64 bpf\_get\_netns\_cookie(void \**ctx*)** - **Description** Retrieve the cookie (generated by the kernel) of the network namespace the input *ctx* is associated with. The network namespace cookie remains stable for its lifetime and provides a global identifier that can be assumed unique. If *ctx* is NULL, then the helper returns the cookie for the initial network namespace. The cookie itself is very similar to that of **bpf\_get\_socket\_cookie**() helper, but for network namespaces instead of sockets. - **Return** A 8-byte long opaque number. - **u64 bpf\_get\_current\_ancestor\_cgroup\_id(int *ancestor\_level*)** - **Description** Return id of cgroup v2 that is ancestor of the cgroup associated with the current task at the *ancestor\_level*. The root cgroup is at *ancestor\_level* zero and each step down the hierarchy increments the level. If *ancestor\_level* == level of cgroup associated with the current task, then return value will be the same as that of **bpf\_get\_current\_cgroup\_id**(). The helper is useful to implement policies based on cgroups that are upper in hierarchy than immediate cgroup associated with the current task. The format of returned id and helper limitations are same as in **bpf\_get\_current\_cgroup\_id**(). - **Return** The id is returned or 0 in case the id could not be retrieved. - **long bpf\_sk\_assign(struct sk\_buff \**skb*, void \**sk*, u64 *flags*)** - **Description** Helper is overloaded depending on BPF program type. This description applies to **BPF\_PROG\_TYPE\_SCHED\_CLS** and **BPF\_PROG\_TYPE\_SCHED\_ACT** programs. Assign the *sk* to the *skb*. When combined with appropriate routing configuration to receive the packet towards the socket, will cause *skb* to be delivered to the specified socket. Subsequent redirection of *skb* via **bpf\_redirect**(), **bpf\_clone\_redirect**() or other methods outside of BPF may interfere with successful delivery to the socket. This operation is only valid from TC ingress path. The *flags* argument must be zero. - **Return** 0 on success, or a negative error in case of failure: **-EINVAL** if specified *flags* are not supported. **-ENOENT** if the socket is unavailable for assignment. **-ENETUNREACH** if the socket is unreachable (wrong netns). **-EOPNOTSUPP** if the operation is not supported, for example a call from outside of TC ingress. - **long bpf\_sk\_assign(struct bpf\_sk\_lookup \**ctx*, struct bpf\_sock \**sk*, u64 *flags*)** - **Description** Helper is overloaded depending on BPF program type. This description applies to **BPF\_PROG\_TYPE\_SK\_LOOKUP** programs. Select the *sk* as a result of a socket lookup. For the operation to succeed passed socket must be compatible with the packet description provided by the *ctx* object. L4 protocol (**IPPROTO\_TCP** or **IPPROTO\_UDP**) must be an exact match. While IP family (**AF\_INET** or **AF\_INET6**) must be compatible, that is IPv6 sockets that are not v6-only can be selected for IPv4 packets. Only TCP listeners and UDP unconnected sockets can be selected. *sk* can also be NULL to reset any previous selection. *flags* argument can combination of following values: - • **BPF\_SK\_LOOKUP\_F\_REPLACE** to override the previous socket selection, potentially done by a BPF program that ran before us. - • **BPF\_SK\_LOOKUP\_F\_NO\_REUSEPORT** to skip load-balancing within reuseport group for the socket being selected. On success *ctx-\>sk* will point to the selected socket. - **Return** 0 on success, or a negative errno in case of failure. - • **-EAFNOSUPPORT** if socket family (*sk-\>family*) is not compatible with packet family (*ctx-\>family*). - • **-EEXIST** if socket has been already selected, potentially by another program, and **BPF\_SK\_LOOKUP\_F\_REPLACE** flag was not specified. - • **-EINVAL** if unsupported flags were specified. - • **-EPROTOTYPE** if socket L4 protocol (*sk-\>protocol*) doesn't match packet protocol (*ctx-\>protocol*). - • **-ESOCKTNOSUPPORT** if socket is not in allowed state (TCP listening or UDP unconnected). - **u64 bpf\_ktime\_get\_boot\_ns(void)** - **Description** Return the time elapsed since system boot, in nanoseconds. Does include the time the system was suspended. See: **clock\_gettime**(**CLOCK\_BOOTTIME**) - **Return** Current *ktime*. - **long bpf\_seq\_printf(struct seq\_file \**m*, const char \**fmt*, u32 *fmt\_size*, const void \**data*, u32 *data\_len*)** - **Description** **bpf\_seq\_printf**() uses seq\_file **seq\_printf**() to print out the format string. The *m* represents the seq\_file. The *fmt* and *fmt\_size* are for the format string itself. The *data* and *data\_len* are format string arguments. The *data* are a **u64** array and corresponding format string values are stored in the array. For strings and pointers where pointees are accessed, only the pointer values are stored in the *data* array. The *data\_len* is the size of *data* in bytes - must be a multiple of 8. Formats **%s**, **%p{i,I}{4,6}** requires to read kernel memory. Reading kernel memory may fail due to either invalid address or valid address but requiring a major memory fault. If reading kernel memory fails, the string for **%s** will be an empty string, and the ip address for **%p{i,I}{4,6}** will be 0. Not returning error to bpf program is consistent with what **bpf\_trace\_printk**() does for now. - **Return** 0 on success, or a negative error in case of failure: **-EBUSY** if per-CPU memory copy buffer is busy, can try again by returning 1 from bpf program. **-EINVAL** if arguments are invalid, or if *fmt* is invalid/unsupported. **-E2BIG** if *fmt* contains too many format specifiers. **-EOVERFLOW** if an overflow happened: The same object will be tried again. - **long bpf\_seq\_write(struct seq\_file \**m*, const void \**data*, u32 *len*)** - **Description** **bpf\_seq\_write**() uses seq\_file **seq\_write**() to write the data. The *m* represents the seq\_file. The *data* and *len* represent the data to write in bytes. - **Return** 0 on success, or a negative error in case of failure: **-EOVERFLOW** if an overflow happened: The same object will be tried again. - **u64 bpf\_sk\_cgroup\_id(void \**sk*)** - **Description** Return the cgroup v2 id of the socket *sk*. *sk* must be a non-**NULL** pointer to a socket, e.g. one returned from **bpf\_sk\_lookup\_xxx**(), **bpf\_sk\_fullsock**(), etc. The format of returned id is same as in **bpf\_skb\_cgroup\_id**(). This helper is available only if the kernel was compiled with the **CONFIG\_SOCK\_CGROUP\_DATA** configuration option. - **Return** The id is returned or 0 in case the id could not be retrieved. - **u64 bpf\_sk\_ancestor\_cgroup\_id(void \**sk*, int *ancestor\_level*)** - **Description** Return id of cgroup v2 that is ancestor of cgroup associated with the *sk* at the *ancestor\_level*. The root cgroup is at *ancestor\_level* zero and each step down the hierarchy increments the level. If *ancestor\_level* == level of cgroup associated with *sk*, then return value will be same as that of **bpf\_sk\_cgroup\_id**(). The helper is useful to implement policies based on cgroups that are upper in hierarchy than immediate cgroup associated with *sk*. The format of returned id and helper limitations are same as in **bpf\_sk\_cgroup\_id**(). - **Return** The id is returned or 0 in case the id could not be retrieved. - **long bpf\_ringbuf\_output(void \**ringbuf*, void \**data*, u64 *size*, u64 *flags*)** - **Description** Copy *size* bytes from *data* into a ring buffer *ringbuf*. If **BPF\_RB\_NO\_WAKEUP** is specified in *flags*, no notification of new data availability is sent. If **BPF\_RB\_FORCE\_WAKEUP** is specified in *flags*, notification of new data availability is sent unconditionally. If **0** is specified in *flags*, an adaptive notification of new data availability is sent. An adaptive notification is a notification sent whenever the user-space process has caught up and consumed all available payloads. In case the user-space process is still processing a previous payload, then no notification is needed as it will process the newly added payload automatically. - **Return** 0 on success, or a negative error in case of failure. - **void \*bpf\_ringbuf\_reserve(void \**ringbuf*, u64 *size*, u64 *flags*)** - **Description** Reserve *size* bytes of payload in a ring buffer *ringbuf*. *flags* must be 0. - **Return** Valid pointer with *size* bytes of memory available; NULL, otherwise. - **void bpf\_ringbuf\_submit(void \**data*, u64 *flags*)** - **Description** Submit reserved ring buffer sample, pointed to by *data*. If **BPF\_RB\_NO\_WAKEUP** is specified in *flags*, no notification of new data availability is sent. If **BPF\_RB\_FORCE\_WAKEUP** is specified in *flags*, notification of new data availability is sent unconditionally. If **0** is specified in *flags*, an adaptive notification of new data availability is sent. See 'bpf\_ringbuf\_output()' for the definition of adaptive notification. - **Return** Nothing. Always succeeds. - **void bpf\_ringbuf\_discard(void \**data*, u64 *flags*)** - **Description** Discard reserved ring buffer sample, pointed to by *data*. If **BPF\_RB\_NO\_WAKEUP** is specified in *flags*, no notification of new data availability is sent. If **BPF\_RB\_FORCE\_WAKEUP** is specified in *flags*, notification of new data availability is sent unconditionally. If **0** is specified in *flags*, an adaptive notification of new data availability is sent. See 'bpf\_ringbuf\_output()' for the definition of adaptive notification. - **Return** Nothing. Always succeeds. - **u64 bpf\_ringbuf\_query(void \**ringbuf*, u64 *flags*)** - **Description** Query various characteristics of provided ring buffer. What exactly is queries is determined by *flags*: - • **BPF\_RB\_AVAIL\_DATA**: Amount of data not yet consumed. - • **BPF\_RB\_RING\_SIZE**: The size of ring buffer. - • **BPF\_RB\_CONS\_POS**: Consumer position (can wrap around). - • **BPF\_RB\_PROD\_POS**: Producer(s) position (can wrap around). Data returned is just a momentary snapshot of actual values and could be inaccurate, so this facility should be used to power heuristics and for reporting, not to make 100% correct calculation. - **Return** Requested value, or 0, if *flags* are not recognized. - **long bpf\_csum\_level(struct sk\_buff \**skb*, u64 *level*)** - **Description** Change the skbs checksum level by one layer up or down, or reset it entirely to none in order to have the stack perform checksum validation. The level is applicable to the following protocols: TCP, UDP, GRE, SCTP, FCOE. For example, a decap of \| ETH \| IP \| UDP \| GUE \| IP \| TCP \| into \| ETH \| IP \| TCP \| through **bpf\_skb\_adjust\_room**() helper with passing in **BPF\_F\_ADJ\_ROOM\_NO\_CSUM\_RESET** flag would require one call to **bpf\_csum\_level**() with **BPF\_CSUM\_LEVEL\_DEC** since the UDP header is removed. Similarly, an encap of the latter into the former could be accompanied by a helper call to **bpf\_csum\_level**() with **BPF\_CSUM\_LEVEL\_INC** if the skb is still intended to be processed in higher layers of the stack instead of just egressing at tc. There are three supported level settings at this time: - • **BPF\_CSUM\_LEVEL\_INC**: Increases skb-\>csum\_level for skbs with CHECKSUM\_UNNECESSARY. - • **BPF\_CSUM\_LEVEL\_DEC**: Decreases skb-\>csum\_level for skbs with CHECKSUM\_UNNECESSARY. - • **BPF\_CSUM\_LEVEL\_RESET**: Resets skb-\>csum\_level to 0 and sets CHECKSUM\_NONE to force checksum validation by the stack. - • **BPF\_CSUM\_LEVEL\_QUERY**: No-op, returns the current skb-\>csum\_level. - **Return** 0 on success, or a negative error in case of failure. In the case of **BPF\_CSUM\_LEVEL\_QUERY**, the current skb-\>csum\_level is returned or the error code -EACCES in case the skb is not subject to CHECKSUM\_UNNECESSARY. - **struct tcp6\_sock \*bpf\_skc\_to\_tcp6\_sock(void \**sk*)** - **Description** Dynamically cast a *sk* pointer to a *tcp6\_sock* pointer. - **Return** *sk* if casting is valid, or **NULL** otherwise. - **struct tcp\_sock \*bpf\_skc\_to\_tcp\_sock(void \**sk*)** - **Description** Dynamically cast a *sk* pointer to a *tcp\_sock* pointer. - **Return** *sk* if casting is valid, or **NULL** otherwise. - **struct tcp\_timewait\_sock \*bpf\_skc\_to\_tcp\_timewait\_sock(void \**sk*)** - **Description** Dynamically cast a *sk* pointer to a *tcp\_timewait\_sock* pointer. - **Return** *sk* if casting is valid, or **NULL** otherwise. - **struct tcp\_request\_sock \*bpf\_skc\_to\_tcp\_request\_sock(void \**sk*)** - **Description** Dynamically cast a *sk* pointer to a *tcp\_request\_sock* pointer. - **Return** *sk* if casting is valid, or **NULL** otherwise. - **struct udp6\_sock \*bpf\_skc\_to\_udp6\_sock(void \**sk*)** - **Description** Dynamically cast a *sk* pointer to a *udp6\_sock* pointer. - **Return** *sk* if casting is valid, or **NULL** otherwise. - **long bpf\_get\_task\_stack(struct task\_struct \**task*, void \**buf*, u32 *size*, u64 *flags*)** - **Description** Return a user or a kernel stack in bpf program provided buffer. Note: the user stack will only be populated if the *task* is the current task; all other tasks will return -EOPNOTSUPP. To achieve this, the helper needs *task*, which is a valid pointer to **struct task\_struct**. To store the stacktrace, the bpf program provides *buf* with a nonnegative *size*. The last argument, *flags*, holds the number of stack frames to skip (from 0 to 255), masked with **BPF\_F\_SKIP\_FIELD\_MASK**. The next bits can be used to set the following flags: - **BPF\_F\_USER\_STACK** Collect a user space stack instead of a kernel stack. The *task* must be the current task. - **BPF\_F\_USER\_BUILD\_ID** Collect buildid+offset instead of ips for user stack, only valid if **BPF\_F\_USER\_STACK** is also specified. **bpf\_get\_task\_stack**() can collect up to **PERF\_MAX\_STACK\_DEPTH** both kernel and user frames, subject to sufficient large buffer size. Note that this limit can be controlled with the **sysctl** program, and that it should be manually increased in order to profile long user stacks (such as stacks for Java programs). To do so, use: ``` # sysctl kernel.perf_event_max_stack= ``` - **Return** The non-negative copied *buf* length equal to or less than *size* on success, or a negative error in case of failure. - **long bpf\_load\_hdr\_opt(struct bpf\_sock\_ops \**skops*, void \**searchby\_res*, u32 *len*, u64 *flags*)** - **Description** Load header option. Support reading a particular TCP header option for bpf program (**BPF\_PROG\_TYPE\_SOCK\_OPS**). If *flags* is 0, it will search the option from the *skops***-\>skb\_data**. The comment in **struct bpf\_sock\_ops** has details on what skb\_data contains under different *skops***-\>op**. The first byte of the *searchby\_res* specifies the kind that it wants to search. If the searching kind is an experimental kind (i.e. 253 or 254 according to RFC6994). It also needs to specify the "magic" which is either 2 bytes or 4 bytes. It then also needs to specify the size of the magic by using the 2nd byte which is "kind-length" of a TCP header option and the "kind-length" also includes the first 2 bytes "kind" and "kind-length" itself as a normal TCP header option also does. For example, to search experimental kind 254 with 2 byte magic 0xeB9F, the searchby\_res should be \[ 254, 4, 0xeB, 0x9F, 0, 0, .... 0 \]. To search for the standard window scale option (3), the *searchby\_res* should be \[ 3, 0, 0, .... 0 \]. Note, kind-length must be 0 for regular option. Searching for No-Op (0) and End-of-Option-List (1) are not supported. *len* must be at least 2 bytes which is the minimal size of a header option. Supported flags: - • **BPF\_LOAD\_HDR\_OPT\_TCP\_SYN** to search from the saved\_syn packet or the just-received syn packet. - **Return** \> 0 when found, the header option is copied to *searchby\_res*. The return value is the total length copied. On failure, a negative error code is returned: **-EINVAL** if a parameter is invalid. **-ENOMSG** if the option is not found. **-ENOENT** if no syn packet is available when **BPF\_LOAD\_HDR\_OPT\_TCP\_SYN** is used. **-ENOSPC** if there is not enough space. Only *len* number of bytes are copied. **-EFAULT** on failure to parse the header options in the packet. **-EPERM** if the helper cannot be used under the current *skops***-\>op**. - **long bpf\_store\_hdr\_opt(struct bpf\_sock\_ops \**skops*, const void \**from*, u32 *len*, u64 *flags*)** - **Description** Store header option. The data will be copied from buffer *from* with length *len* to the TCP header. The buffer *from* should have the whole option that includes the kind, kind-length, and the actual option data. The *len* must be at least kind-length long. The kind-length does not have to be 4 byte aligned. The kernel will take care of the padding and setting the 4 bytes aligned value to th-\>doff. This helper will check for duplicated option by searching the same option in the outgoing skb. This helper can only be called during **BPF\_SOCK\_OPS\_WRITE\_HDR\_OPT\_CB**. - **Return** 0 on success, or negative error in case of failure: **-EINVAL** If param is invalid. **-ENOSPC** if there is not enough space in the header. Nothing has been written **-EEXIST** if the option already exists. **-EFAULT** on failure to parse the existing header options. **-EPERM** if the helper cannot be used under the current *skops***-\>op**. - **long bpf\_reserve\_hdr\_opt(struct bpf\_sock\_ops \**skops*, u32 *len*, u64 *flags*)** - **Description** Reserve *len* bytes for the bpf header option. The space will be used by **bpf\_store\_hdr\_opt**() later in **BPF\_SOCK\_OPS\_WRITE\_HDR\_OPT\_CB**. If **bpf\_reserve\_hdr\_opt**() is called multiple times, the total number of bytes will be reserved. This helper can only be called during **BPF\_SOCK\_OPS\_HDR\_OPT\_LEN\_CB**. - **Return** 0 on success, or negative error in case of failure: **-EINVAL** if a parameter is invalid. **-ENOSPC** if there is not enough space in the header. **-EPERM** if the helper cannot be used under the current *skops***-\>op**. - **void \*bpf\_inode\_storage\_get(struct bpf\_map \**map*, void \**inode*, void \**value*, u64 *flags*)** - **Description** Get a bpf\_local\_storage from an *inode*. Logically, it could be thought of as getting the value from a *map* with *inode* as the **key**. From this perspective, the usage is not much different from **bpf\_map\_lookup\_elem**(*map*, **&***inode*) except this helper enforces the key must be an inode and the map must also be a **BPF\_MAP\_TYPE\_INODE\_STORAGE**. Underneath, the value is stored locally at *inode* instead of the *map*. The *map* is used as the bpf-local-storage "type". The bpf-local-storage "type" (i.e. the *map*) is searched against all bpf\_local\_storage residing at *inode*. An optional *flags* (**BPF\_LOCAL\_STORAGE\_GET\_F\_CREATE**) can be used such that a new bpf\_local\_storage will be created if one does not exist. *value* can be used together with **BPF\_LOCAL\_STORAGE\_GET\_F\_CREATE** to specify the initial value of a bpf\_local\_storage. If *value* is **NULL**, the new bpf\_local\_storage will be zero initialized. - **Return** A bpf\_local\_storage pointer is returned on success. **NULL** if not found or there was an error in adding a new bpf\_local\_storage. - **int bpf\_inode\_storage\_delete(struct bpf\_map \**map*, void \**inode*)** - **Description** Delete a bpf\_local\_storage from an *inode*. - **Return** 0 on success. **-ENOENT** if the bpf\_local\_storage cannot be found. - **long bpf\_d\_path(const struct path \**path*, char \**buf*, u32 *sz*)** - **Description** Return full path for given **struct path** object, which needs to be the kernel BTF *path* object. The path is returned in the provided buffer *buf* of size *sz* and is zero terminated. - **Return** On success, the strictly positive length of the string, including the trailing NUL character. On error, a negative value. - **long bpf\_copy\_from\_user(void \**dst*, u32 *size*, const void \**user\_ptr*)** - **Description** Read *size* bytes from user space address *user\_ptr* and store the data in *dst*. This is a wrapper of **copy\_from\_user**(). - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_snprintf\_btf(char \**str*, u32 *str\_size*, struct btf\_ptr \**ptr*, u32 *btf\_ptr\_size*, u64 *flags*)** - **Description** Use BTF to store a string representation of *ptr*-\>ptr in *str*, using *ptr*-\>type\_id. This value should specify the type that *ptr*-\>ptr points to. LLVM \_\_builtin\_btf\_type\_id(type, 1) can be used to look up vmlinux BTF type ids. Traversing the data structure using BTF, the type information and values are stored in the first *str\_size* - 1 bytes of *str*. Safe copy of the pointer data is carried out to avoid kernel crashes during operation. Smaller types can use string space on the stack; larger programs can use map data to store the string representation. The string can be subsequently shared with userspace via bpf\_perf\_event\_output() or ring buffer interfaces. bpf\_trace\_printk() is to be avoided as it places too small a limit on string size to be useful. *flags* is a combination of - **BTF\_F\_COMPACT** no formatting around type information - **BTF\_F\_NONAME** no struct/union member names/types - **BTF\_F\_PTR\_RAW** show raw (unobfuscated) pointer values; equivalent to printk specifier %px. - **BTF\_F\_ZERO** show zero-valued struct/union members; they are not displayed by default - **Return** The number of bytes that were written (or would have been written if output had to be truncated due to string size), or a negative error in cases of failure. - **long bpf\_seq\_printf\_btf(struct seq\_file \**m*, struct btf\_ptr \**ptr*, u32 *ptr\_size*, u64 *flags*)** - **Description** Use BTF to write to seq\_write a string representation of *ptr*-\>ptr, using *ptr*-\>type\_id as per bpf\_snprintf\_btf(). *flags* are identical to those used for bpf\_snprintf\_btf. - **Return** 0 on success or a negative error in case of failure. - **u64 bpf\_skb\_cgroup\_classid(struct sk\_buff \**skb*)** - **Description** See **bpf\_get\_cgroup\_classid**() for the main description. This helper differs from **bpf\_get\_cgroup\_classid**() in that the cgroup v1 net\_cls class is retrieved only from the *skb*'s associated socket instead of the current process. - **Return** The id is returned or 0 in case the id could not be retrieved. - **long bpf\_redirect\_neigh(u32 *ifindex*, struct bpf\_redir\_neigh \**params*, int *plen*, u64 *flags*)** - **Description** Redirect the packet to another net device of index *ifindex* and fill in L2 addresses from neighboring subsystem. This helper is somewhat similar to **bpf\_redirect**(), except that it populates L2 addresses as well, meaning, internally, the helper relies on the neighbor lookup for the L2 address of the nexthop. The helper will perform a FIB lookup based on the skb's networking header to get the address of the next hop, unless this is supplied by the caller in the *params* argument. The *plen* argument indicates the len of *params* and should be set to 0 if *params* is NULL. The *flags* argument is reserved and must be 0. The helper is currently only supported for tc BPF program types, and enabled for IPv4 and IPv6 protocols. - **Return** The helper returns **TC\_ACT\_REDIRECT** on success or **TC\_ACT\_SHOT** on error. - **void \*bpf\_per\_cpu\_ptr(const void \**percpu\_ptr*, u32 *cpu*)** - **Description** Take a pointer to a percpu ksym, *percpu\_ptr*, and return a pointer to the percpu kernel variable on *cpu*. A ksym is an extern variable decorated with '\_\_ksym'. For ksym, there is a global var (either static or global) defined of the same name in the kernel. The ksym is percpu if the global var is percpu. The returned pointer points to the global percpu var on *cpu*. bpf\_per\_cpu\_ptr() has the same semantic as per\_cpu\_ptr() in the kernel, except that bpf\_per\_cpu\_ptr() may return NULL. This happens if *cpu* is larger than nr\_cpu\_ids. The caller of bpf\_per\_cpu\_ptr() must check the returned value. - **Return** A pointer pointing to the kernel percpu variable on *cpu*, or NULL, if *cpu* is invalid. - **void \*bpf\_this\_cpu\_ptr(const void \**percpu\_ptr*)** - **Description** Take a pointer to a percpu ksym, *percpu\_ptr*, and return a pointer to the percpu kernel variable on this cpu. See the description of 'ksym' in **bpf\_per\_cpu\_ptr**(). bpf\_this\_cpu\_ptr() has the same semantic as this\_cpu\_ptr() in the kernel. Different from **bpf\_per\_cpu\_ptr**(), it would never return NULL. - **Return** A pointer pointing to the kernel percpu variable on this cpu. - **long bpf\_redirect\_peer(u32 *ifindex*, u64 *flags*)** - **Description** Redirect the packet to another net device of index *ifindex*. This helper is somewhat similar to **bpf\_redirect**(), except that the redirection happens to the *ifindex*' peer device and the netns switch takes place from ingress to ingress without going through the CPU's backlog queue. *skb***-\>mark** and *skb***-\>tstamp** are not cleared during the netns switch. The *flags* argument is reserved and must be 0. The helper is currently only supported for tc BPF program types at the ingress hook and for veth and netkit target device types. The peer device must reside in a different network namespace. - **Return** The helper returns **TC\_ACT\_REDIRECT** on success or **TC\_ACT\_SHOT** on error. - **void \*bpf\_task\_storage\_get(struct bpf\_map \**map*, struct task\_struct \**task*, void \**value*, u64 *flags*)** - **Description** Get a bpf\_local\_storage from the *task*. Logically, it could be thought of as getting the value from a *map* with *task* as the **key**. From this perspective, the usage is not much different from **bpf\_map\_lookup\_elem**(*map*, **&***task*) except this helper enforces the key must be a task\_struct and the map must also be a **BPF\_MAP\_TYPE\_TASK\_STORAGE**. Underneath, the value is stored locally at *task* instead of the *map*. The *map* is used as the bpf-local-storage "type". The bpf-local-storage "type" (i.e. the *map*) is searched against all bpf\_local\_storage residing at *task*. An optional *flags* (**BPF\_LOCAL\_STORAGE\_GET\_F\_CREATE**) can be used such that a new bpf\_local\_storage will be created if one does not exist. *value* can be used together with **BPF\_LOCAL\_STORAGE\_GET\_F\_CREATE** to specify the initial value of a bpf\_local\_storage. If *value* is **NULL**, the new bpf\_local\_storage will be zero initialized. - **Return** A bpf\_local\_storage pointer is returned on success. **NULL** if not found or there was an error in adding a new bpf\_local\_storage. - **long bpf\_task\_storage\_delete(struct bpf\_map \**map*, struct task\_struct \**task*)** - **Description** Delete a bpf\_local\_storage from a *task*. - **Return** 0 on success. **-ENOENT** if the bpf\_local\_storage cannot be found. - **struct task\_struct \*bpf\_get\_current\_task\_btf(void)** - **Description** Return a BTF pointer to the "current" task. This pointer can also be used in helpers that accept an *ARG\_PTR\_TO\_BTF\_ID* of type *task\_struct*. - **Return** Pointer to the current task. - **long bpf\_bprm\_opts\_set(struct linux\_binprm \**bprm*, u64 *flags*)** - **Description** Set or clear certain options on *bprm*: **BPF\_F\_BPRM\_SECUREEXEC** Set the secureexec bit which sets the **AT\_SECURE** auxv for glibc. The bit is cleared if the flag is not specified. - **Return** **-EINVAL** if invalid *flags* are passed, zero otherwise. - **u64 bpf\_ktime\_get\_coarse\_ns(void)** - **Description** Return a coarse-grained version of the time elapsed since system boot, in nanoseconds. Does not include time the system was suspended. See: **clock\_gettime**(**CLOCK\_MONOTONIC\_COARSE**) - **Return** Current *ktime*. - **long bpf\_ima\_inode\_hash(struct inode \**inode*, void \**dst*, u32 *size*)** - **Description** Returns the stored IMA hash of the *inode* (if it's available). If the hash is larger than *size*, then only *size* bytes will be copied to *dst* - **Return** The **hash\_algo** is returned on success, **-EOPNOTSUPP** if IMA is disabled or **-EINVAL** if invalid arguments are passed. - **struct socket \*bpf\_sock\_from\_file(struct file \**file*)** - **Description** If the given file represents a socket, returns the associated socket. - **Return** A pointer to a struct socket on success or NULL if the file is not a socket. - **long bpf\_check\_mtu(void \**ctx*, u32 *ifindex*, u32 \**mtu\_len*, s32 *len\_diff*, u64 *flags*)** - **Description** Check packet size against exceeding MTU of net device (based on *ifindex*). This helper will likely be used in combination with helpers that adjust/change the packet size. The argument *len\_diff* can be used for querying with a planned size change. This allows to check MTU prior to changing packet ctx. Providing a *len\_diff* adjustment that is larger than the actual packet size (resulting in negative packet size) will in principle not exceed the MTU, which is why it is not considered a failure. Other BPF helpers are needed for performing the planned size change; therefore the responsibility for catching a negative packet size belongs in those helpers. Specifying *ifindex* zero means the MTU check is performed against the current net device. This is practical if this isn't used prior to redirect. On input *mtu\_len* must be a valid pointer, else verifier will reject BPF program. If the value *mtu\_len* is initialized to zero then the ctx packet size is use. When value *mtu\_len* is provided as input this specify the L3 length that the MTU check is done against. Remember XDP and TC length operate at L2, but this value is L3 as this correlate to MTU and IP-header tot\_len values which are L3 (similar behavior as bpf\_fib\_lookup). The Linux kernel route table can configure MTUs on a more specific per route level, which is not provided by this helper. For route level MTU checks use the **bpf\_fib\_lookup**() helper. *ctx* is either **struct xdp\_md** for XDP programs or **struct sk\_buff** for tc cls\_act programs. The *flags* argument can be a combination of one or more of the following values: - **BPF\_MTU\_CHK\_SEGS** This flag will only works for *ctx* **struct sk\_buff**. If packet context contains extra packet segment buffers (often knows as GSO skb), then MTU check is harder to check at this point, because in transmit path it is possible for the skb packet to get re-segmented (depending on net device features). This could still be a MTU violation, so this flag enables performing MTU check against segments, with a different violation return code to tell it apart. Check cannot use len\_diff. On return *mtu\_len* pointer contains the MTU value of the net device. Remember the net device configured MTU is the L3 size, which is returned here and XDP and TC length operate at L2. Helper take this into account for you, but remember when using MTU value in your BPF-code. - **Return** - • 0 on success, and populate MTU value in *mtu\_len* pointer. - • \< 0 if any input argument is invalid (*mtu\_len* not updated) MTU violations return positive values, but also populate MTU value in *mtu\_len* pointer, as this can be needed for implementing PMTU handing: - • **BPF\_MTU\_CHK\_RET\_FRAG\_NEEDED** - • **BPF\_MTU\_CHK\_RET\_SEGS\_TOOBIG** - **long bpf\_for\_each\_map\_elem(struct bpf\_map \**map*, void \**callback\_fn*, void \**callback\_ctx*, u64 *flags*)** - **Description** For each element in **map**, call **callback\_fn** function with **map**, **callback\_ctx** and other map-specific parameters. The **callback\_fn** should be a static function and the **callback\_ctx** should be a pointer to the stack. The **flags** is used to control certain aspects of the helper. Currently, the **flags** must be 0. The following are a list of supported map types and their respective expected callback signatures: BPF\_MAP\_TYPE\_HASH, BPF\_MAP\_TYPE\_PERCPU\_HASH, BPF\_MAP\_TYPE\_LRU\_HASH, BPF\_MAP\_TYPE\_LRU\_PERCPU\_HASH, BPF\_MAP\_TYPE\_ARRAY, BPF\_MAP\_TYPE\_PERCPU\_ARRAY long (\*callback\_fn)(struct bpf\_map \*map, const void \*key, void \*value, void \*ctx); For per\_cpu maps, the map\_value is the value on the cpu where the bpf\_prog is running. If **callback\_fn** return 0, the helper will continue to the next element. If return value is 1, the helper will skip the rest of elements and return. Other return values are not used now. - **Return** The number of traversed map elements for success, **-EINVAL** for invalid **flags**. - **long bpf\_snprintf(char \**str*, u32 *str\_size*, const char \**fmt*, u64 \**data*, u32 *data\_len*)** - **Description** Outputs a string into the **str** buffer of size **str\_size** based on a format string stored in a read-only map pointed by **fmt**. Each format specifier in **fmt** corresponds to one u64 element in the **data** array. For strings and pointers where pointees are accessed, only the pointer values are stored in the *data* array. The *data\_len* is the size of *data* in bytes - must be a multiple of 8. Formats **%s** and **%p{i,I}{4,6}** require to read kernel memory. Reading kernel memory may fail due to either invalid address or valid address but requiring a major memory fault. If reading kernel memory fails, the string for **%s** will be an empty string, and the ip address for **%p{i,I}{4,6}** will be 0. Not returning error to bpf program is consistent with what **bpf\_trace\_printk**() does for now. - **Return** The strictly positive length of the formatted string, including the trailing zero character. If the return value is greater than **str\_size**, **str** contains a truncated string, guaranteed to be zero-terminated except when **str\_size** is 0. Or **-EBUSY** if the per-CPU memory copy buffer is busy. - **long bpf\_sys\_bpf(u32 *cmd*, void \**attr*, u32 *attr\_size*)** - **Description** Execute bpf syscall with given arguments. - **Return** A syscall result. - **long bpf\_btf\_find\_by\_name\_kind(char \**name*, int *name\_sz*, u32 *kind*, int *flags*)** - **Description** Find BTF type with given name and kind in vmlinux BTF or in module's BTFs. - **Return** Returns btf\_id and btf\_obj\_fd in lower and upper 32 bits. - **long bpf\_sys\_close(u32 *fd*)** - **Description** Execute close syscall for given FD. - **Return** A syscall result. - **long bpf\_timer\_init(struct bpf\_timer \**timer*, struct bpf\_map \**map*, u64 *flags*)** - **Description** Initialize the timer. First 4 bits of *flags* specify clockid. Only CLOCK\_MONOTONIC, CLOCK\_REALTIME, CLOCK\_BOOTTIME are allowed. All other bits of *flags* are reserved. The verifier will reject the program if *timer* is not from the same *map*. - **Return** 0 on success. **-EBUSY** if *timer* is already initialized. **-EINVAL** if invalid *flags* are passed. **-EPERM** if *timer* is in a map that doesn't have any user references. The user space should either hold a file descriptor to a map with timers or pin such map in bpffs. When map is unpinned or file descriptor is closed all timers in the map will be cancelled and freed. - **long bpf\_timer\_set\_callback(struct bpf\_timer \**timer*, void \**callback\_fn*)** - **Description** Configure the timer to call *callback\_fn* static function. - **Return** 0 on success. **-EINVAL** if *timer* was not initialized with bpf\_timer\_init() earlier. **-EPERM** if *timer* is in a map that doesn't have any user references. The user space should either hold a file descriptor to a map with timers or pin such map in bpffs. When map is unpinned or file descriptor is closed all timers in the map will be cancelled and freed. - **long bpf\_timer\_start(struct bpf\_timer \**timer*, u64 *nsecs*, u64 *flags*)** - **Description** Set timer expiration N nanoseconds from the current time. The configured callback will be invoked in soft irq context on some cpu and will not repeat unless another bpf\_timer\_start() is made. In such case the next invocation can migrate to a different cpu. Since struct bpf\_timer is a field inside map element the map owns the timer. The bpf\_timer\_set\_callback() will increment refcnt of BPF program to make sure that callback\_fn code stays valid. When user space reference to a map reaches zero all timers in a map are cancelled and corresponding program's refcnts are decremented. This is done to make sure that Ctrl-C of a user process doesn't leave any timers running. If map is pinned in bpffs the callback\_fn can re-arm itself indefinitely. bpf\_map\_update/delete\_elem() helpers and user space sys\_bpf commands cancel and free the timer in the given map element. The map can contain timers that invoke callback\_fn-s from different programs. The same callback\_fn can serve different timers from different maps if key/value layout matches across maps. Every bpf\_timer\_set\_callback() can have different callback\_fn. *flags* can be one of: - **BPF\_F\_TIMER\_ABS** Start the timer in absolute expire value instead of the default relative one. - **BPF\_F\_TIMER\_CPU\_PIN** Timer will be pinned to the CPU of the caller. - **Return** 0 on success. **-EINVAL** if *timer* was not initialized with bpf\_timer\_init() earlier or invalid *flags* are passed. - **long bpf\_timer\_cancel(struct bpf\_timer \**timer*)** - **Description** Cancel the timer and wait for callback\_fn to finish if it was running. - **Return** 0 if the timer was not active. 1 if the timer was active. **-EINVAL** if *timer* was not initialized with bpf\_timer\_init() earlier. **-EDEADLK** if callback\_fn tried to call bpf\_timer\_cancel() on its own timer which would have led to a deadlock otherwise. - **u64 bpf\_get\_func\_ip(void \**ctx*)** - **Description** Get address of the traced function (for tracing and kprobe programs). When called for kprobe program attached as uprobe it returns probe address for both entry and return uprobe. - **Return** Address of the traced function for kprobe. 0 for kprobes placed within the function (not at the entry). Address of the probe for uprobe and return uprobe. - **u64 bpf\_get\_attach\_cookie(void \**ctx*)** - **Description** Get bpf\_cookie value provided (optionally) during the program attachment. It might be different for each individual attachment, even if BPF program itself is the same. Expects BPF program context *ctx* as a first argument. - **Supported for the following program types:** - • kprobe/uprobe; - • tracepoint; - • perf\_event. - **Return** Value specified by user at BPF link creation/attachment time or 0, if it was not specified. - **long bpf\_task\_pt\_regs(struct task\_struct \**task*)** - **Description** Get the struct pt\_regs associated with **task**. - **Return** A pointer to struct pt\_regs. - **long bpf\_get\_branch\_snapshot(void \**entries*, u32 *size*, u64 *flags*)** - **Description** Get branch trace from hardware engines like Intel LBR. The hardware engine is stopped shortly after the helper is called. Therefore, the user need to filter branch entries based on the actual use case. To capture branch trace before the trigger point of the BPF program, the helper should be called at the beginning of the BPF program. The data is stored as struct perf\_branch\_entry into output buffer *entries*. *size* is the size of *entries* in bytes. *flags* is reserved for now and must be zero. - **Return** On success, number of bytes written to *buf*. On error, a negative value. **-EINVAL** if *flags* is not zero. **-ENOENT** if architecture does not support branch records. - **long bpf\_trace\_vprintk(const char \**fmt*, u32 *fmt\_size*, const void \**data*, u32 *data\_len*)** - **Description** Behaves like **bpf\_trace\_printk**() helper, but takes an array of u64 to format and can handle more format args as a result. Arguments are to be used as in **bpf\_seq\_printf**() helper. - **Return** The number of bytes written to the buffer, or a negative error in case of failure. - **struct unix\_sock \*bpf\_skc\_to\_unix\_sock(void \**sk*)** - **Description** Dynamically cast a *sk* pointer to a *unix\_sock* pointer. - **Return** *sk* if casting is valid, or **NULL** otherwise. - **long bpf\_kallsyms\_lookup\_name(const char \**name*, int *name\_sz*, int *flags*, u64 \**res*)** - **Description** Get the address of a kernel symbol, returned in *res*. *res* is set to 0 if the symbol is not found. - **Return** On success, zero. On error, a negative value. **-EINVAL** if *flags* is not zero. **-EINVAL** if string *name* is not the same size as *name\_sz*. **-ENOENT** if symbol is not found. **-EPERM** if caller does not have permission to obtain kernel address. - **long bpf\_find\_vma(struct task\_struct \**task*, u64 *addr*, void \**callback\_fn*, void \**callback\_ctx*, u64 *flags*)** - **Description** Find vma of *task* that contains *addr*, call *callback\_fn* function with *task*, *vma*, and *callback\_ctx*. The *callback\_fn* should be a static function and the *callback\_ctx* should be a pointer to the stack. The *flags* is used to control certain aspects of the helper. Currently, the *flags* must be 0. The expected callback signature is long (\*callback\_fn)(struct task\_struct \*task, struct vm\_area\_struct \*vma, void \*callback\_ctx); - **Return** 0 on success. **-ENOENT** if *task-\>mm* is NULL, or no vma contains *addr*. **-EBUSY** if failed to try lock mmap\_lock. **-EINVAL** for invalid **flags**. - **long bpf\_loop(u32 *nr\_loops*, void \**callback\_fn*, void \**callback\_ctx*, u64 *flags*)** - **Description** For **nr\_loops**, call **callback\_fn** function with **callback\_ctx** as the context parameter. The **callback\_fn** should be a static function and the **callback\_ctx** should be a pointer to the stack. The **flags** is used to control certain aspects of the helper. Currently, the **flags** must be 0. Currently, nr\_loops is limited to 1 \<\< 23 (~8 million) loops. long (\*callback\_fn)(u64 index, void \*ctx); where **index** is the current index in the loop. The index is zero-indexed. If **callback\_fn** returns 0, the helper will continue to the next loop. If return value is 1, the helper will skip the rest of the loops and return. Other return values are not used now, and will be rejected by the verifier. - **Return** The number of loops performed, **-EINVAL** for invalid **flags**, **-E2BIG** if **nr\_loops** exceeds the maximum number of loops. - **long bpf\_strncmp(const char \**s1*, u32 *s1\_sz*, const char \**s2*)** - **Description** Do strncmp() between **s1** and **s2**. **s1** doesn't need to be null-terminated and **s1\_sz** is the maximum storage size of **s1**. **s2** must be a read-only string. - **Return** An integer less than, equal to, or greater than zero if the first **s1\_sz** bytes of **s1** is found to be less than, to match, or be greater than **s2**. - **long bpf\_get\_func\_arg(void \**ctx*, u32 *n*, u64 \**value*)** - **Description** Get **n**-th argument register (zero based) of the traced function (for tracing programs) returned in **value**. - **Return** 0 on success. **-EINVAL** if n \>= argument register count of traced function. - **long bpf\_get\_func\_ret(void \**ctx*, u64 \**value*)** - **Description** Get return value of the traced function (for tracing programs) in **value**. - **Return** 0 on success. **-EOPNOTSUPP** for tracing programs other than BPF\_TRACE\_FEXIT or BPF\_MODIFY\_RETURN. - **long bpf\_get\_func\_arg\_cnt(void \**ctx*)** - **Description** Get number of registers of the traced function (for tracing programs) where function arguments are stored in these registers. - **Return** The number of argument registers of the traced function. - **int bpf\_get\_retval(void)** - **Description** Get the BPF program's return value that will be returned to the upper layers. This helper is currently supported by cgroup programs and only by the hooks where BPF program's return value is returned to the userspace via errno. - **Return** The BPF program's return value. - **int bpf\_set\_retval(int *retval*)** - **Description** Set the BPF program's return value that will be returned to the upper layers. This helper is currently supported by cgroup programs and only by the hooks where BPF program's return value is returned to the userspace via errno. Note that there is the following corner case where the program exports an error via bpf\_set\_retval but signals success via 'return 1': bpf\_set\_retval(-EPERM); return 1; In this case, the BPF program's return value will use helper's -EPERM. This still holds true for cgroup/bind{4,6} which supports extra 'return 3' success case. - **Return** 0 on success, or a negative error in case of failure. - **u64 bpf\_xdp\_get\_buff\_len(struct xdp\_buff \**xdp\_md*)** - **Description** Get the total size of a given xdp buff (linear and paged area) - **Return** The total size of a given xdp buffer. - **long bpf\_xdp\_load\_bytes(struct xdp\_buff \**xdp\_md*, u32 *offset*, void \**buf*, u32 *len*)** - **Description** This helper is provided as an easy way to load data from a xdp buffer. It can be used to load *len* bytes from *offset* from the frame associated to *xdp\_md*, into the buffer pointed by *buf*. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_xdp\_store\_bytes(struct xdp\_buff \**xdp\_md*, u32 *offset*, void \**buf*, u32 *len*)** - **Description** Store *len* bytes from buffer *buf* into the frame associated to *xdp\_md*, at *offset*. - **Return** 0 on success, or a negative error in case of failure. - **long bpf\_copy\_from\_user\_task(void \**dst*, u32 *size*, const void \**user\_ptr*, struct task\_struct \**tsk*, u64 *flags*)** - **Description** Read *size* bytes from user space address *user\_ptr* in *tsk*'s address space, and stores the data in *dst*. *flags* is not used yet and is provided for future extensibility. This helper can only be used by sleepable programs. - **Return** 0 on success, or a negative error in case of failure. On error *dst* buffer is zeroed out. - **long bpf\_skb\_set\_tstamp(struct sk\_buff \**skb*, u64 *tstamp*, u32 *tstamp\_type*)** - **Description** Change the \_\_sk\_buff-\>tstamp\_type to *tstamp\_type* and set *tstamp* to the \_\_sk\_buff-\>tstamp together. If there is no need to change the \_\_sk\_buff-\>tstamp\_type, the tstamp value can be directly written to \_\_sk\_buff-\>tstamp instead. BPF\_SKB\_TSTAMP\_DELIVERY\_MONO is the only tstamp that will be kept during bpf\_redirect\_\*(). A non zero *tstamp* must be used with the BPF\_SKB\_TSTAMP\_DELIVERY\_MONO *tstamp\_type*. A BPF\_SKB\_TSTAMP\_UNSPEC *tstamp\_type* can only be used with a zero *tstamp*. Only IPv4 and IPv6 skb-\>protocol are supported. This function is most useful when it needs to set a mono delivery time to \_\_sk\_buff-\>tstamp and then bpf\_redirect\_\*() to the egress of an iface. For example, changing the (rcv) timestamp in \_\_sk\_buff-\>tstamp at ingress to a mono delivery time and then bpf\_redirect\_\*() to \. - **Return** 0 on success. **-EINVAL** for invalid input **-EOPNOTSUPP** for unsupported protocol - **long bpf\_ima\_file\_hash(struct file \**file*, void \**dst*, u32 *size*)** - **Description** Returns a calculated IMA hash of the *file*. If the hash is larger than *size*, then only *size* bytes will be copied to *dst* - **Return** The **hash\_algo** is returned on success, **-EOPNOTSUPP** if the hash calculation failed or **-EINVAL** if invalid arguments are passed. - **void \*bpf\_kptr\_xchg(void \**dst*, void \**ptr*)** - **Description** Exchange kptr at pointer *dst* with *ptr*, and return the old value. *dst* can be map value or local kptr. *ptr* can be NULL, otherwise it must be a referenced pointer which will be released when this helper is called. - **Return** The old value of kptr (which can be NULL). The returned pointer if not NULL, is a reference which must be released using its corresponding release function, or moved into a BPF map before program exit. - **void \*bpf\_map\_lookup\_percpu\_elem(struct bpf\_map \**map*, const void \**key*, u32 *cpu*)** - **Description** Perform a lookup in *percpu map* for an entry associated to *key* on *cpu*. - **Return** Map value associated to *key* on *cpu*, or **NULL** if no entry was found or *cpu* is invalid. - **struct mptcp\_sock \*bpf\_skc\_to\_mptcp\_sock(void \**sk*)** - **Description** Dynamically cast a *sk* pointer to a *mptcp\_sock* pointer. - **Return** *sk* if casting is valid, or **NULL** otherwise. - **long bpf\_dynptr\_from\_mem(void \**data*, u64 *size*, u64 *flags*, struct bpf\_dynptr \**ptr*)** - **Description** Get a dynptr to local memory *data*. *data* must be a ptr to a map value. The maximum *size* supported is DYNPTR\_MAX\_SIZE. *flags* is currently unused. - **Return** 0 on success, -E2BIG if the size exceeds DYNPTR\_MAX\_SIZE, -EINVAL if flags is not 0. - **long bpf\_ringbuf\_reserve\_dynptr(void \**ringbuf*, u32 *size*, u64 *flags*, struct bpf\_dynptr \**ptr*)** - **Description** Reserve *size* bytes of payload in a ring buffer *ringbuf* through the dynptr interface. *flags* must be 0. Please note that a corresponding bpf\_ringbuf\_submit\_dynptr or bpf\_ringbuf\_discard\_dynptr must be called on *ptr*, even if the reservation fails. This is enforced by the verifier. - **Return** 0 on success, or a negative error in case of failure. - **void bpf\_ringbuf\_submit\_dynptr(struct bpf\_dynptr \**ptr*, u64 *flags*)** - **Description** Submit reserved ring buffer sample, pointed to by *data*, through the dynptr interface. This is a no-op if the dynptr is invalid/null. For more information on *flags*, please see 'bpf\_ringbuf\_submit'. - **Return** Nothing. Always succeeds. - **void bpf\_ringbuf\_discard\_dynptr(struct bpf\_dynptr \**ptr*, u64 *flags*)** - **Description** Discard reserved ring buffer sample through the dynptr interface. This is a no-op if the dynptr is invalid/null. For more information on *flags*, please see 'bpf\_ringbuf\_discard'. - **Return** Nothing. Always succeeds. - **long bpf\_dynptr\_read(void \**dst*, u64 *len*, const struct bpf\_dynptr \**src*, u64 *offset*, u64 *flags*)** - **Description** Read *len* bytes from *src* into *dst*, starting from *offset* into *src*. *flags* is currently unused. - **Return** 0 on success, -E2BIG if *offset* + *len* exceeds the length of *src*'s data, -EINVAL if *src* is an invalid dynptr or if *flags* is not 0. - **long bpf\_dynptr\_write(const struct bpf\_dynptr \**dst*, u64 *offset*, void \**src*, u64 *len*, u64 *flags*)** - **Description** Write *len* bytes from *src* into *dst*, starting from *offset* into *dst*. *flags* must be 0 except for skb-type dynptrs. - **For skb-type dynptrs:** - • All data slices of the dynptr are automatically invalidated after **bpf\_dynptr\_write**(). This is because writing may pull the skb and change the underlying packet buffer. - • For *flags*, please see the flags accepted by **bpf\_skb\_store\_bytes**(). - **Return** 0 on success, -E2BIG if *offset* + *len* exceeds the length of *dst*'s data, -EINVAL if *dst* is an invalid dynptr or if *dst* is a read-only dynptr or if *flags* is not correct. For skb-type dynptrs, other errors correspond to errors returned by **bpf\_skb\_store\_bytes**(). - **void \*bpf\_dynptr\_data(const struct bpf\_dynptr \**ptr*, u64 *offset*, u64 *len*)** - **Description** Get a pointer to the underlying dynptr data. *len* must be a statically known value. The returned data slice is invalidated whenever the dynptr is invalidated. skb and xdp type dynptrs may not use bpf\_dynptr\_data. They should instead use bpf\_dynptr\_slice and bpf\_dynptr\_slice\_rdwr. - **Return** Pointer to the underlying dynptr data, NULL if the dynptr is read-only, if the dynptr is invalid, or if the offset and length is out of bounds. - **s64 bpf\_tcp\_raw\_gen\_syncookie\_ipv4(struct iphdr \**iph*, struct tcphdr \**th*, u32 *th\_len*)** - **Description** Try to issue a SYN cookie for the packet with corresponding IPv4/TCP headers, *iph* and *th*, without depending on a listening socket. *iph* points to the IPv4 header. *th* points to the start of the TCP header, while *th\_len* contains the length of the TCP header (at least **sizeof**(**struct tcphdr**)). - **Return** On success, lower 32 bits hold the generated SYN cookie in followed by 16 bits which hold the MSS value for that cookie, and the top 16 bits are unused. On failure, the returned value is one of the following: **-EINVAL** if *th\_len* is invalid. - **s64 bpf\_tcp\_raw\_gen\_syncookie\_ipv6(struct ipv6hdr \**iph*, struct tcphdr \**th*, u32 *th\_len*)** - **Description** Try to issue a SYN cookie for the packet with corresponding IPv6/TCP headers, *iph* and *th*, without depending on a listening socket. *iph* points to the IPv6 header. *th* points to the start of the TCP header, while *th\_len* contains the length of the TCP header (at least **sizeof**(**struct tcphdr**)). - **Return** On success, lower 32 bits hold the generated SYN cookie in followed by 16 bits which hold the MSS value for that cookie, and the top 16 bits are unused. On failure, the returned value is one of the following: **-EINVAL** if *th\_len* is invalid. **-EPROTONOSUPPORT** if CONFIG\_IPV6 is not builtin. - **long bpf\_tcp\_raw\_check\_syncookie\_ipv4(struct iphdr \**iph*, struct tcphdr \**th*)** - **Description** Check whether *iph* and *th* contain a valid SYN cookie ACK without depending on a listening socket. *iph* points to the IPv4 header. *th* points to the TCP header. - **Return** 0 if *iph* and *th* are a valid SYN cookie ACK. On failure, the returned value is one of the following: **-EACCES** if the SYN cookie is not valid. - **long bpf\_tcp\_raw\_check\_syncookie\_ipv6(struct ipv6hdr \**iph*, struct tcphdr \**th*)** - **Description** Check whether *iph* and *th* contain a valid SYN cookie ACK without depending on a listening socket. *iph* points to the IPv6 header. *th* points to the TCP header. - **Return** 0 if *iph* and *th* are a valid SYN cookie ACK. On failure, the returned value is one of the following: **-EACCES** if the SYN cookie is not valid. **-EPROTONOSUPPORT** if CONFIG\_IPV6 is not builtin. - **u64 bpf\_ktime\_get\_tai\_ns(void)** - **Description** A nonsettable system-wide clock derived from wall-clock time but ignoring leap seconds. This clock does not experience discontinuities and backwards jumps caused by NTP inserting leap seconds as CLOCK\_REALTIME does. See: **clock\_gettime**(**CLOCK\_TAI**) - **Return** Current *ktime*. - **long bpf\_user\_ringbuf\_drain(struct bpf\_map \**map*, void \**callback\_fn*, void \**ctx*, u64 *flags*)** - **Description** Drain samples from the specified user ring buffer, and invoke the provided callback for each such sample: long (\*callback\_fn)(const struct bpf\_dynptr \*dynptr, void \*ctx); If **callback\_fn** returns 0, the helper will continue to try and drain the next sample, up to a maximum of BPF\_MAX\_USER\_RINGBUF\_SAMPLES samples. If the return value is 1, the helper will skip the rest of the samples and return. Other return values are not used now, and will be rejected by the verifier. - **Return** The number of drained samples if no error was encountered while draining samples, or 0 if no samples were present in the ring buffer. If a user-space producer was epoll-waiting on this map, and at least one sample was drained, they will receive an event notification notifying them of available space in the ring buffer. If the BPF\_RB\_NO\_WAKEUP flag is passed to this function, no wakeup notification will be sent. If the BPF\_RB\_FORCE\_WAKEUP flag is passed, a wakeup notification will be sent even if no sample was drained. On failure, the returned value is one of the following: **-EBUSY** if the ring buffer is contended, and another calling context was concurrently draining the ring buffer. **-EINVAL** if user-space is not properly tracking the ring buffer due to the producer position not being aligned to 8 bytes, a sample not being aligned to 8 bytes, or the producer position not matching the advertised length of a sample. **-E2BIG** if user-space has tried to publish a sample which is larger than the size of the ring buffer, or which cannot fit within a struct bpf\_dynptr. - **void \*bpf\_cgrp\_storage\_get(struct bpf\_map \**map*, struct cgroup \**cgroup*, void \**value*, u64 *flags*)** - **Description** Get a bpf\_local\_storage from the *cgroup*. Logically, it could be thought of as getting the value from a *map* with *cgroup* as the **key**. From this perspective, the usage is not much different from **bpf\_map\_lookup\_elem**(*map*, **&***cgroup*) except this helper enforces the key must be a cgroup struct and the map must also be a **BPF\_MAP\_TYPE\_CGRP\_STORAGE**. In reality, the local-storage value is embedded directly inside of the *cgroup* object itself, rather than being located in the **BPF\_MAP\_TYPE\_CGRP\_STORAGE** map. When the local-storage value is queried for some *map* on a *cgroup* object, the kernel will perform an O(n) iteration over all of the live local-storage values for that *cgroup* object until the local-storage value for the *map* is found. An optional *flags* (**BPF\_LOCAL\_STORAGE\_GET\_F\_CREATE**) can be used such that a new bpf\_local\_storage will be created if one does not exist. *value* can be used together with **BPF\_LOCAL\_STORAGE\_GET\_F\_CREATE** to specify the initial value of a bpf\_local\_storage. If *value* is **NULL**, the new bpf\_local\_storage will be zero initialized. - **Return** A bpf\_local\_storage pointer is returned on success. **NULL** if not found or there was an error in adding a new bpf\_local\_storage. - **long bpf\_cgrp\_storage\_delete(struct bpf\_map \**map*, struct cgroup \**cgroup*)** - **Description** Delete a bpf\_local\_storage from a *cgroup*. - **Return** 0 on success. **-ENOENT** if the bpf\_local\_storage cannot be found. ## EXAMPLES Example usage for most of the eBPF helpers listed in this manual page are available within the Linux kernel sources, at the following locations: - • *samples/bpf/* - • *tools/testing/selftests/bpf/* ## LICENSE eBPF programs can have an associated license, passed along with the bytecode instructions to the kernel when the programs are loaded. The format for that string is identical to the one in use for kernel modules (Dual licenses, such as "Dual BSD/GPL", may be used). Some helper functions are only accessible to programs that are compatible with the GNU General Public License (GNU GPL). In order to use such helpers, the eBPF program must be loaded with the correct license string passed (via **attr**) to the **bpf**() system call, and this generally translates into the C source code of the program containing a line similar to the following: ``` char ____license[] __attribute__((section("license"), used)) = "GPL"; ``` ## IMPLEMENTATION This manual page is an effort to document the existing eBPF helper functions. But as of this writing, the BPF sub-system is under heavy development. New eBPF program or map types are added, along with new helper functions. Some helpers are occasionally made available for additional program types. So in spite of the efforts of the community, this page might not be up-to-date. If you want to check by yourself what helper functions exist in your kernel, or what types of programs they can support, here are some files among the kernel tree that you may be interested in: - • *include/uapi/linux/bpf.h* is the main BPF header. It contains the full list of all helper functions, as well as many other BPF definitions including most of the flags, structs or constants used by the helpers. - • *net/core/filter.c* contains the definition of most network-related helper functions, and the list of program types from which they can be used. - • *kernel/trace/bpf\_trace.c* is the equivalent for most tracing program-related helpers. - • *kernel/bpf/verifier.c* contains the functions used to check that valid types of eBPF maps are used with a given helper function. - • *kernel/bpf/* directory contains other files in which additional helpers are defined (for cgroups, sockmaps, etc.). - • The bpftool utility can be used to probe the availability of helper functions on the system (as well as supported program and map types, and a number of other parameters). To do so, run **bpftool feature probe** (see [**bpftool-feature**(8)](/bpftool-feature/8.md) for details). Add the **unprivileged** keyword to list features available to unprivileged users. Compatibility between helper functions and program types can generally be found in the files where helper functions are defined. Look for the **struct** **bpf\_func\_proto** objects and for functions returning them: these functions contain a list of helpers that a given program type can call. Note that the **default:** label of the **switch ... case** used to filter helpers can call other functions, themselves allowing access to additional helpers. The requirement for GPL license is also in those **struct bpf\_func\_proto**. Compatibility between helper functions and map types can be found in the **check\_map\_func\_compatibility**() function in file *kernel/bpf/verifier.c*. Helper functions that invalidate the checks on **data** and **data\_end** pointers for network processing are listed in function **bpf\_helper\_changes\_pkt\_data**() in file *net/core/filter.c*. ## SEE ALSO [**bpf**(2)](/bpf/2.md), [**bpftool**(8)](/bpftool/8.md), [**cgroups**(7)](/cgroups/7.md), [**ip**(8)](/ip/8.md), [**perf\_event\_open**(2)](/perf_event_open/2.md), [**sendmsg**(2)](/sendmsg/2.md), [**socket**(7)](/socket/7.md), [**tc-bpf**(8)](/tc-bpf/8.md)