--- name: "stats" section: "3" platform: "freebsd" package: "base" version: "16.0-CURRENT-20261027-61c70dc16a79" release: "FreeBSD 16.0-CURRENT (2026-10-27)" platforms: ["freebsd"] url: "https://new.carta.tech/STATS_VSS_CRHIST32_LIN" --- # stats(3) statistics gathering Part of [STATS\_VSS\_CRHIST32\_LIN(3)](/STATS_VSS_CRHIST32_LIN/3.md). ## NAME **stats** – statistics gathering ## LIBRARY library “libstats” ## SYNOPSIS **#include \** **#include \** **#include \** ### Stats Blob Template Management Functions *int*\ **stats\_tpl\_alloc**(*const char \*name*, *uint32\_t flags*); *int*\ **stats\_tpl\_fetch\_allocid**(*const char \*name*, *uint32\_t hash*); *int*\ **stats\_tpl\_fetch**(*int tpl\_id*, *struct statsblob\_tpl \*\*tpl*); *int*\ **stats\_tpl\_id2name**(*uint32\_t tpl\_id*, *char \*buf*, *size\_t len*); *int*\ **stats\_tpl\_sample\_rates**(*SYSCTL\_HANDLER\_ARGS*); *int*\ **stats\_tpl\_sample\_rollthedice**(*struct stats\_tpl\_sample\_rate \*rates*, *int nrates*, *void \*seed\_bytes*, *size\_t seed\_len*); *struct* *voistatspec*\ **STATS\_VSS\_SUM**(); *struct* *voistatspec*\ **STATS\_VSS\_MAX**(); *struct* *voistatspec*\ **STATS\_VSS\_MIN**(); *struct* *voistatspec*\ **STATS\_VSS\_CRHIST\<32\|64\>\_LIN**(*lb*, *ub*, *stepinc*, *vsdflags*); *struct* *voistatspec*\ **STATS\_VSS\_CRHIST\<32\|64\>\_EXP**(*lb*, *ub*, *stepbase*, *stepexp*, *vsdflags*); *struct* *voistatspec*\ **STATS\_VSS\_CRHIST\<32\|64\>\_LINEXP**(*lb*, *ub*, *nlinsteps*, *stepbase*, *vsdflags*); *struct* *voistatspec*\ **STATS\_VSS\_CRHIST\<32\|64\>\_USR**(**HBKTS**(**CRBKT**( *lb*), *...*),*vsdflags*); *struct* *voistatspec*\ **STATS\_VSS\_DRHIST\<32\|64\>\_USR**(**HBKTS**(**DRBKT**( *lb*, *ub*), *...*),*vsdflags*); *struct* *voistatspec*\ **STATS\_VSS\_DVHIST\<32\|64\>\_USR**(**HBKTS**(**DVBKT**( *val*), *...*),*vsdflags*); *struct* *voistatspec*\ **STATS\_VSS\_TDGSTCLUST\<32\|64\>**(*nctroids*, *prec*); *int*\ **stats\_tpl\_add\_voistats**(*uint32\_t tpl\_id*, *int32\_t voi\_id*, *const char \*voi\_name*, *enum vsd\_dtype voi\_dtype*, *uint32\_t nvss*, *struct voistatspec \*vss*, *uint32\_t flags*); ### Stats Blob Data Gathering Functions *int*\ **stats\_voi\_update\_\\_\**(*struct statsblob \*sb*, *int32\_t voi\_id*, *\ voival*); ### Stats Blob Utility Functions *struct* *statsblob* *\**\ **stats\_blob\_alloc**(*uint32\_t tpl\_id*, *uint32\_t flags*); *int*\ **stats\_blob\_init**(*struct statsblob \*sb*, *uint32\_t tpl\_id*, *uint32\_t flags*); *int*\ **stats\_blob\_clone**(*struct statsblob \*\*dst*, *size\_t dstmaxsz*, *struct statsblob \*src*, *uint32\_t flags*); *void*\ **stats\_blob\_destroy**(*struct statsblob \*sb*); *int*\ **stats\_voistat\_fetch\_dptr**(*struct statsblob \*sb*, *int32\_t voi\_id*, *enum voi\_stype stype*, *enum vsd\_dtype \*retdtype*, *struct voistatdata \*\*retvsd*, *size\_t \*retvsdsz*); *int*\ **stats\_voistat\_fetch\_\**(*struct statsblob \*sb*, *int32\_t voi\_id*, *enum voi\_stype stype*, *\ \*ret*); *int*\ **stats\_blob\_snapshot**(*struct statsblob \*\*dst*, *size\_t dstmaxsz*, *struct statsblob \*src*, *uint32\_t flags*); *int*\ **stats\_blob\_tostr**(*struct statsblob \*sb*, *struct sbuf \*buf*, *enum sb\_str\_fmt fmt*, *uint32\_t flags*); *int*\ **stats\_voistatdata\_tostr**(*const struct voistatdata \*vsd*, *enum vsd\_dtype dtype*, *enum sb\_str\_fmt fmt*, *struct sbuf \*buf*, *int objdump*); *typedef* *int*\ **\*stats\_blob\_visitcb\_t**(*struct sb\_visit \*sbv*, *void \*usrctx*); *int*\ **stats\_blob\_visit**(*struct statsblob \*sb*, *stats\_blob\_visitcb\_t func*, *void \*usrctx*); ## DESCRIPTION The **stats** framework facilitates real-time kernel and user space statistics gathering. The framework is built around the “statsblob”, an object embedded within a contiguous memory allocation that is mostly opaque to consumers and stores all required state. A “statsblob” object can itself be embedded within other objects either directly or indirectly using a pointer. Objects or subsystems for which statistics are to be gathered are initialized from a template “statsblob”, which acts as the blueprint for an arbitrary set of Variables Of Interest (VOIs) and their associated statistics. Each template defines a schema plus associated metadata, which are kept separate to minimize the memory footprint of blobs. Data gathering hook functions added at appropriate locations within the code base of interest feed VOI data into the framework for processing. Each “statsblob”, consists of a *struct* *statsblob* header and opaque internal blob structure per the following diagram: ``` --------------------------------------------------------- | struct | uint8_t | | statsblob | opaque[] | --------------------------------------------------------- ``` The publicly visible 8-byte header is defined as: ``` struct statsblob { uint8_t abi; uint8_t endian; uint16_t flags; uint16_t maxsz; uint16_t cursz; uint8_t opaque[]; }; ``` *abi* specifies which API version the blob's *opaque* internals conform to (STATS\_ABI\_V1 is the only version currently defined). *endian* specifies the endianness of the blob's fields( SB\_LE for little endian, SB\_BE for big endian, or SB\_UE for unknown endianness). *cursz* specifies the size of the blob, while *maxsz* specifies the size of the underlying memory allocation in which the blob is embedded. Both *cursz* and *maxsz* default to units of bytes, unless a flag is set in *flags* that dictates otherwise. Templates are constructed by associating arbitrary VOI IDs with a set of statistics, where each statistic is specified using a *struct* *voistatspec* per the definition below: ``` struct voistatspec { vss_hlpr_fn hlpr; struct vss_hlpr_info *hlprinfo; struct voistatdata *iv; size_t vsdsz; uint32_t flags; enum vsd_dtype vs_dtype : 8; enum voi_stype stype : 8; }; ``` It is generally expected that consumers will not work with *struct* *voistatspec* directly, and instead use the **STATS\_VSS\_\***() helper macros. The **stats** framework offers the following statistics for association with VOIs: - VS\_STYPE\_SUM The sum of VOI values. - VS\_STYPE\_MAX The maximum VOI value. - VS\_STYPE\_MIN The minimum VOI value. - VS\_STYPE\_HIST A static bucket histogram of VOI values, including a count of “out-of-band/bucket” values which did not match any bucket. Histograms can be specified as “*C*ontinuous *R*ange” (CRHIST), “*D*iscrete *R*ange” (DRHIST) or “*D*iscrete *V*alue” (DVHIST), with 32 or 64 bit bucket counters, depending on the VOI semantics. - VS\_STYPE\_TDGST A dynamic bucket histogram of VOI values based on the t-digest method (refer to the t-digest paper in the SEE ALSO section below). A“visitor software design pattern” -like scheme is employed to facilitate iterating over a blob's data without concern for the blob's structure. The data provided to visitor callback functions is encapsulated in *struct* *sb\_visit* per the definition below: ``` struct sb_visit { struct voistatdata *vs_data; uint32_t tplhash; uint32_t flags; int16_t voi_id; int16_t vs_dsz; enum vsd_dtype voi_dtype : 8; enum vsd_dtype vs_dtype : 8; int8_t vs_stype; uint16_t vs_errs; }; ``` The **stats\_tpl\_sample\_rates**() and **stats\_tpl\_sample\_rollthedice**() functions utilize *struct* *stats\_tpl\_sample\_rate* to encapsulate per-template sample rate information per the definition below: ``` struct stats_tpl_sample_rate { int32_t tpl_slot_id; uint32_t tpl_sample_pct; }; ``` The *tpl\_slot\_id* member holds the template's slot ID obtained from **stats\_tpl\_alloc**() or **stats\_tpl\_fetch\_allocid**(). The *tpl\_sample\_pct* member holds the template's sample rate as an integer percentage in the range \[0,100\]. The *stats\_tpl\_sr\_cb\_t* conformant function pointer that is required as the *arg1* of **stats\_tpl\_sample\_rates**() is defined as: ``` enum stats_tpl_sr_cb_action { TPL_SR_UNLOCKED_GET, TPL_SR_RLOCKED_GET, TPL_SR_RUNLOCK, TPL_SR_PUT }; typedef int (*stats_tpl_sr_cb_t)(enum stats_tpl_sr_cb_action action, struct stats_tpl_sample_rate **rates, int *nrates, void *ctx); ``` It is required that a conformant function: - Return an appropriate [errno(2)](/errno/2.md) on error, otherwise 0. - When called with "action == TPL\_SR\_\*\_GET", return the subsystem's rates list ptr and count, locked or unlocked as requested. - When called with "action == TPL\_SR\_RUNLOCK", unlock the subsystem's rates list ptr and count. Pair with a prior "action == TPL\_SR\_RLOCKED\_GET" call. - When called with "action == TPL\_SR\_PUT", update the subsystem's rates list ptr and count to the sysctl processed values and return the inactive list details in *rates* and *nrates* for garbage collection by **stats\_tpl\_sample\_rates**(). Where templates need to be referenced via textual means, for example via a MIB variable, the following string based template spec formats can be used: 1. "\" :\, for example"TCP\_DEFAULT" :1731235399 2. "\", for example "TCP\_DEFAULT" 3. :\, for example :1731235399 The first form is the normative spec format generated by the framework, while the second and third forms are convenience formats primarily for user input. The use of inverted commas around the template name is optional. ### MIB Variables The in-kernel **stats** framework exposes the following framework-specific variables in the *kern.stats* branch of the [sysctl(3)](/sysctl/3.md) MIB. - templates Read-only CSV list of registered templates in normative template spec form. ### Template Management Functions The **stats\_tpl\_alloc**() function allocates a new template with the specified unique name and returns its runtime-stable template slot ID for use with other API functions. The *flags* argument is currently unused. The **stats\_tpl\_fetch\_allocid**() function returns the runtime-stable template slot ID of any registered template matching the specified name and hash. The **stats\_tpl\_fetch**() function returns the pointer to the registered template object at the specified template slot ID. The **stats\_tpl\_id2name**() function returns the name of the registered template object at the specified template slot ID. The **stats\_tpl\_sample\_rates**() function provides a generic handler for template sample rates management and reporting via [sysctl(3)](/sysctl/3.md) MIB variables. Subsystems can use this function to create a subsystem-specific [SYSCTL\_PROC(9)](/SYSCTL_PROC/9.md) MIB variable that manages and reports subsystem-specific template sampling rates. Subsystems must supply a *stats\_tpl\_sr\_cb\_t* conformant function pointer as the sysctl's *arg1*, which is a callback used to interact with the subsystem's stats template sample rates list. Subsystems can optionally specify the sysctl's *arg2* as non-zero, which causes a zero-initialized allocation of arg2-sized contextual memory to be heap-allocated and passed in to all subsystem callbacks made during the operation of **stats\_tpl\_sample\_rates**(). The **stats\_tpl\_sample\_rollthedice**() function makes a weighted random template selection from the supplied array of template sampling rates. The cumulative percentage of all sampling rates should not exceed 100. If no seed is supplied, a PRNG is used to generate a true random number so that every selection is independent. If a seed is supplied, selection will be made randomly across different seeds, but deterministically given the same seed. The **stats\_tpl\_add\_voistats**() function is used to add a VOI and associated set of statistics to the registered template object at the specified template slot ID. The set of statistics is passed as an array of *struct* *voistatspec* which can be initialized using the **STATS\_VSS\_\***() helper macros or manually for non-standard use cases. For static *vss* arrays, the *nvss* count of array elements can be determined by passing *vss* to the **NVSS**() macro. The SB\_VOI\_RELUPDATE flag can be passed to configure the VOI for use with **stats\_voi\_update\_rel\_\**(), which entails maintaining an extra 8 bytes of state in the blob at each update. ### Data Gathering Functions The **stats\_voi\_update\_abs\_\**() and **stats\_voi\_update\_rel\_\**() functions both update all the statistics associated with the VOI identified by *voi\_id*. The “abs” call uses *voival* as an absolute value, whereas the “rel” call uses *voival* as a value relative to that of the previous update function call, by adding it to the previous value and using the result for the update. Relative updates are only possible for VOIs that were added to the template with the SB\_VOI\_RELUPDATE flag specified to **stats\_tpl\_add\_voistats**(). ### Utility Functions The **stats\_blob\_alloc**() function allocates and initializes a new blob based on the registered template object at the specified template slot ID. The **stats\_blob\_init**() function initializes a new blob in an existing memory allocation based on the registered template object at the specified template slot ID. The **stats\_blob\_clone**() function duplicates the *src* blob into *dst*, leaving only the *maxsz* field of *dst* untouched. The SB\_CLONE\_ALLOCDST flag can be passed to instruct the function to allocate a new blob of appropriate size into which to clone *src*, storing the new pointer in *\*dst*. The SB\_CLONE\_USRDSTNOFAULT or SB\_CLONE\_USRDST flags can be set to respectively signal that [copyout\_nofault(9)](/copyout_nofault/9.md) or [copyout(9)](/copyout/9.md) should be used because *\*dst* is a user space address. The **stats\_blob\_snapshot**() function calls **stats\_blob\_clone**() to obtain a copy of *src* and then performs any additional functions required to produce a coherent blob snapshot. The flags interpreted by **stats\_blob\_clone**() also apply to **stats\_blob\_snapshot**(). Additionally, the SB\_CLONE\_RSTSRC flag can be used to effect a reset of the *src* blob's statistics after a snapshot is successfully taken. The **stats\_blob\_destroy**() function destroys a blob previously created with **stats\_blob\_alloc**(), **stats\_blob\_clone**() or **stats\_blob\_snapshot**(). The **stats\_blob\_visit**() function allows the caller to iterate over the contents of a blob. The callback function *func* is called for every VOI and statistic in the blob, passing a *struct* *sb\_visit* and the user context argument *usrctx* to the callback function. The *sbv* passed to the callback function may have one or more of the following flags set in the *flags* struct member to provide useful metadata about the iteration: SB\_IT\_FIRST\_CB, SB\_IT\_LAST\_CB, SB\_IT\_FIRST\_VOI, SB\_IT\_LAST\_VOI, SB\_IT\_FIRST\_VOISTAT, SB\_IT\_LAST\_VOISTAT, SB\_IT\_NULLVOI and SB\_IT\_NULLVOISTAT. Returning a non-zero value from the callback function terminates the iteration. The **stats\_blob\_tostr**() renders a string representation of a blob into the [sbuf(9)](/sbuf/9.md) *buf*. Currently supported render formats are SB\_STRFMT\_FREEFORM and SB\_STRFMT\_JSON. The SB\_TOSTR\_OBJDUMP flag can be passed to render version specific opaque implementation detail for debugging or string-to-binary blob reconstruction purposes. The SB\_TOSTR\_META flag can be passed to render template metadata into the string representation, using the blob's template hash to lookup the corresponding template. The **stats\_voistatdata\_tostr**() renders a string representation of an individual statistic's data into the [sbuf(9)](/sbuf/9.md) *buf*. The same render formats supported by the **stats\_blob\_tostr**() function can be specified, and the *objdump* boolean has the same meaning as the SB\_TOSTR\_OBJDUMP flag. The **stats\_voistat\_fetch\_dptr**() function returns an internal blob pointer to the specified *stype* statistic data for the VOI *voi\_id*. The **stats\_voistat\_fetch\_\**() functions are convenience wrappers around **stats\_voistat\_fetch\_dptr**() to perform the extraction for simple data types. ## IMPLEMENTATION NOTES The following notes apply to STATS\_ABI\_V1 format statsblobs. ### Space-Time Complexity Blobs are laid out as three distinct memory regions following the header: ``` ------------------------------------------------------ | struct | struct | struct | struct | | statsblobv1 | voi [] | voistat [] | voistatdata [] | ------------------------------------------------------ ``` Blobs store VOI and statistic blob state( 8 bytes for *struct* *voi* and 8 bytes for *struct* *voistat* respectively) in sparse arrays, using the *voi\_id* and *enum* *voi\_stype* as array indices. This allows O(1) access to any voi/voistat pair in the blob, at the expense of 8 bytes of wasted memory per vacant slot for templates which do not specify contiguously numbered VOIs and/or statistic types. Data storage for statistics is only allocated for non-vacant slot pairs. To provide a concrete example, a blob with the following specification: - Two VOIs; ID 0 and 2; added to the template in that order - VOI 0 is of data type *int64\_t*, is configured with SB\_VOI\_RELUPDATE to enable support for relative updates using **stats\_voi\_update\_rel\_\**(), and has a VS\_STYPE\_MIN statistic associated with it. - VOI 2 is of data type *uint32\_t* with VS\_STYPE\_SUM and VS\_STYPE\_MAX statistics associated with it. would have the following memory layout: ``` -------------------------------------- | header | struct statsblobv1, 32 bytes |------------------------------------| | voi[0] | struct voi, 8 bytes | voi[1] (vacant) | struct voi, 8 bytes | voi[2] | struct voi, 8 bytes |------------------------------------| | voi[2]voistat[VOISTATE] (vacant) | struct voistat, 8 bytes | voi[2]voistat[SUM] | struct voistat, 8 bytes | voi[2]voistat[MAX] | struct voistat, 8 bytes | voi[0]voistat[VOISTATE] | struct voistat, 8 bytes | voi[0]voistat[SUM] (vacant) | struct voistat, 8 bytes | voi[0]voistat[MAX] (vacant) | struct voistat, 8 bytes | voi[0]voistat[MIN] | struct voistat, 8 bytes |------------------------------------| | voi[2]voistat[SUM]voistatdata | struct voistatdata_int32, 4 bytes | voi[2]voistat[MAX]voistatdata | struct voistatdata_int32, 4 bytes | voi[0]voistat[VOISTATE]voistatdata | struct voistatdata_numeric, 8 bytes | voi[0]voistat[MIN]voistatdata | struct voistatdata_int64, 8 bytes -------------------------------------- TOTAL 136 bytes ``` When rendered to string format using **stats\_blob\_tostr**(), the SB\_STRFMT\_FREEFORM *fmt* and the SB\_TOSTR\_OBJDUMP flag, the rendered output is: ``` struct statsblobv1@0x8016250a0, abi=1, endian=1, maxsz=136, cursz=136, \ created=6294158585626144, lastrst=6294158585626144, flags=0x0000, \ stats_off=56, statsdata_off=112, tplhash=2994056564 vois[0]: id=0, name="", flags=0x0001, dtype=INT_S64, voistatmaxid=3, \ stats_off=80 vois[0]stat[0]: stype=VOISTATE, flags=0x0000, dtype=VOISTATE, \ dsz=8, data_off=120 voistatdata: prev=0 vois[0]stat[1]: stype=-1 vois[0]stat[2]: stype=-1 vois[0]stat[3]: stype=MIN, flags=0x0000, dtype=INT_S64, \ dsz=8, data_off=128 voistatdata: 9223372036854775807 vois[1]: id=-1 vois[2]: id=2, name="", flags=0x0000, dtype=INT_U32, voistatmaxid=2, \ stats_off=56 vois[2]stat[0]: stype=-1 vois[2]stat[1]: stype=SUM, flags=0x0000, dtype=INT_U32, dsz=4, \ data_off=112 voistatdata: 0 vois[2]stat[2]: stype=MAX, flags=0x0000, dtype=INT_U32, dsz=4, \ data_off=116 voistatdata: 0 ``` Note: The "\\" present in the rendered output above indicates a manual line break inserted to keep the man page within 80 columns and is not part of the actual output. ### Locking The **stats** framework does not provide any concurrency protection at the individual blob level, instead requiring that consumers guarantee mutual exclusion when calling API functions that reference a non-template blob. The list of templates is protected with a [rwlock(9)](/rwlock/9.md) in-kernel, and [pthread(3)](/pthread/3.md) rw lock in user space to support concurrency between template management and blob initialization operations. ## RETURN VALUES **stats\_tpl\_alloc**() returns a runtime-stable template slot ID on success, or a negative errno on failure. -EINVAL is returned if any problems are detected with the arguments. -EEXIST is returned if an existing template is registered with the same name. -ENOMEM is returned if a required memory allocation fails. **stats\_tpl\_fetch\_allocid**() returns a runtime-stable template slot ID, or negative errno on failure. -ESRCH is returned if no registered template matches the specified name and/or hash. **stats\_tpl\_fetch**() returns 0 on success, or ENOENT if an invalid *tpl\_id* is specified. **stats\_tpl\_id2name**() returns 0 on success, or an errno on failure. EOVERFLOW is returned if the length of *buf* specified by *len* is too short to hold the template's name. ENOENT is returned if an invalid *tpl\_id* is specified. **stats\_tpl\_sample\_rollthedice**() returns a valid template slot id selected from *rates* or -1 if a NULL selection was made, that is no stats collection this roll. **stats\_tpl\_add\_voistats**() return 0 on success, or an errno on failure. EINVAL is returned if any problems are detected with the arguments. EFBIG is returned if the resulting blob would have exceeded the maximum size. EOPNOTSUPP is returned if an attempt is made to add more VOI stats to a previously configured VOI. ENOMEM is returned if a required memory allocation fails. **stats\_voi\_update\_abs\_\**() and **stats\_voi\_update\_rel\_\**() return 0 on success, or EINVAL if any problems are detected with the arguments. **stats\_blob\_init**() returns 0 on success, or an errno on failure. EINVAL is returned if any problems are detected with the arguments. EOVERFLOW is returned if the template blob's *cursz* is larger than the *maxsz* of the blob being initialized. **stats\_blob\_alloc**() returns a pointer to a newly allocated and initialized blob based on the specified template with slot ID *tpl\_id*, or NULL if the memory allocation failed. **stats\_blob\_clone**() and **stats\_blob\_snapshot**() return 0 on success, or an errno on failure. EINVAL is returned if any problems are detected with the arguments. ENOMEM is returned if the SB\_CLONE\_ALLOCDST flag was specified and the memory allocation for *dst* fails. EOVERFLOW is returned if the src blob's *cursz* is larger than the *maxsz* of the *dst* blob. **stats\_blob\_visit**() returns 0 on success, or EINVAL if any problems are detected with the arguments. **stats\_blob\_tostr**() and **stats\_voistatdata\_tostr**() return 0 on success, or an errno on failure. EINVAL is returned if any problems are detected with the arguments, otherwise any error returned by **sbuf\_error**() for *buf* is returned. **stats\_voistat\_fetch\_dptr**() returns 0 on success, or EINVAL if any problems are detected with the arguments. **stats\_voistat\_fetch\_\**() returns 0 on success, or an errno on failure. EINVAL is returned if any problems are detected with the arguments. EFTYPE is returned if the requested data type does not match the blob's data type for the specified *voi\_id* and *stype*. ## SEE ALSO [errno(2)](/errno/2.md), [arb(3)](/arb/3.md), [qmath(3)](/qmath/3.md), [tcp(4)](/tcp/4.md), [sbuf(9)](/sbuf/9.md) Ted Dunning and Otmar Ertl, *Computing Extremely Accurate Quantiles Using t-digests*, https://github.com/tdunning/t-digest/raw/master/docs/t-digest-paper/histo.pdf. ## HISTORY The **stats** framework first appeared in FreeBSD 13.0. ## AUTHORS The **stats** framework and this manual page were written by Lawrence Stewart ⟨*lstewart@FreeBSD.org*⟩ and sponsored by Netflix, Inc. ## CAVEATS Granularity of timing-dependent network statistics, in particular TCP\_RTT, depends on the HZ timer. To minimize the measurement error avoid using HZ lower than 1000.