---
name: "crypto_buffer_len"
section: "9"
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/CRYPTO_HAS_OUTPUT_BUFFER"
---

# crypto\_buffer\_len(9)

symmetric cryptographic request buffers

Part of [CRYPTO\_HAS\_OUTPUT\_BUFFER(9)](/CRYPTO_HAS_OUTPUT_BUFFER/9.md).

## NAME

**crypto\_buffer** – symmetric cryptographic request buffers

## SYNOPSIS

**#include \<opencrypto/cryptodev.h\>**

*int*\

**crypto\_apply**(*struct cryptop \*crp*, *int off*, *int len*, *int (\*f)(void \*, void \*, u\_int)*, *void \*arg*);

*int*\

**crypto\_apply\_buf**(*struct crypto\_buffer \*cb*, *int off*, *int len*, *int (\*f)(void \*, void \*, u\_int)*, *void \*arg*);

*void* *\**\

**crypto\_buffer\_contiguous\_subsegment**(*struct crypto\_buffer \*cb*, *size\_t skip*, *size\_t len*);

*size\_t*\

**crypto\_buffer\_len**(*struct crypto\_buffer \*cb*);

*void* *\**\

**crypto\_contiguous\_subsegment**(*struct cryptop \*crp*, *size\_t skip*, *size\_t len*);

*void*\

**crypto\_cursor\_init**(*struct crypto\_buffer\_cursor \*cc*, *const struct crypto\_buffer \*cb*);

*void*\

**crypto\_cursor\_advance**(*struct crypto\_buffer\_cursor \*cc*, *size\_t amount*);

*void*\

**crypto\_cursor\_copyback**(*struct crypto\_buffer\_cursor \*cc*, *int size*, *const void \*src*);

*void*\

**crypto\_cursor\_copydata**(*struct crypto\_buffer\_cursor \*cc*, *int size*, *void \*dst*);

*void*\

**crypto\_cursor\_copydata\_noadv**(*struct crypto\_buffer\_cursor \*cc*, *int size*, *void \*dst*);

*void* *\**\

**crypto\_cursor\_segment**(*struct crypto\_buffer\_cursor \*cc*, *size\_t \*len*);

*void*\

**crypto\_cursor\_copy**(*const struct crypto\_buffer\_cursor \*fromc*, *struct crypto\_buffer\_cursor \*toc*);

*bool*\

**CRYPTO\_HAS\_OUTPUT\_BUFFER**(*struct cryptop \*crp*);

## DESCRIPTION

Symmetric cryptographic requests use data buffers to describe the data to be modified. Requests can either specify a single data buffer whose contents are modified in place, or requests may specify separate data buffers for input and output. *struct* *crypto\_buffer* provides an abstraction that permits cryptographic requests to operate on different types of buffers. *struct* *crypto\_cursor* allows cryptographic drivers to iterate over a data buffer.

**CRYPTO\_HAS\_OUTPUT\_BUFFER**() returns true if *crp* uses separate buffers for input and output and false if *crp* uses a single buffer.

**crypto\_buffer\_len**() returns the length of data buffer *cb* in bytes.

**crypto\_apply\_buf**() invokes a caller-supplied function to a region of the data buffer *cb*. The function *f* is called one or more times. For each invocation, the first argument to *f* is the value of *arg* passed to **crypto\_apply\_buf**(). The second and third arguments to *f* are a pointer and length to a segment of the buffer mapped into the kernel. The function is called enough times to cover the *len* bytes of the data buffer which starts at an offset *off*. If any invocation of *f* returns a non-zero value, **crypto\_apply\_buf**() immediately returns that value without invoking *f* on any remaining segments of the region, otherwise **crypto\_apply\_buf**() returns the value from the final call to *f*. **crypto\_apply**() invokes the callback *f* on a region of the input data buffer for *crp*.

**crypto\_buffer\_contiguous\_subsegment**() attempts to locate a single, virtually-contiguous segment of the data buffer *cb*. The segment must be *len* bytes long and start at an offset of *skip* bytes. If a segment is found, a pointer to the start of the segment is returned. Otherwise, NULL is returned. **crypto\_contiguous\_subsegment**() attempts to locate a single, virtually-contiguous segment in the input data buffer for *crp*.

### Data Buffers

Data buffers are described by an instance of *struct* *crypto* *buffer*. The *cb\_type* member contains the type of the data buffer. The following types are supported:

- CRYPTO\_BUF\_NONE

  An invalid buffer. Used to mark the output buffer when a crypto request uses a single data buffer.

- CRYPTO\_BUF\_CONTIG

  An array of bytes mapped into the kernel's address space.

- CRYPTO\_BUF\_UIO

  A scatter/gather list of kernel buffers as described in [uio(9)](/uio/9.md).

- CRYPTO\_BUF\_MBUF

  A chain of network memory buffers as described in [mbuf(9)](/mbuf/9.md).

- CRYPTO\_BUF\_SINGLE\_MBUF

  A single network memory buffer as described in [mbuf(9)](/mbuf/9.md).

- CRYPTO\_BUF\_VMPAGE

  A scatter/gather list of *vm\_page\_t* structures describing pages in the kernel's address space. This buffer type is only available if CRYPTO\_HAS\_VMPAGE is true.

The structure also contains the following type-specific fields:

- *cb\_buf*

  A pointer to the start of a CRYPTO\_BUF\_CONTIG data buffer.

- *cb\_buf\_len*

  The length of a CRYPTO\_BUF\_CONTIG data buffer

- *cb\_mbuf*

  A pointer to a *struct* *mbuf* for CRYPTO\_BUF\_MBUF and CRYPTO\_BUF\_SINGLE\_MBUF.

- *cb\_uio*

  A pointer to a *struct* *uio* for CRYPTO\_BUF\_UIO.

- *cb\_vm\_page*

  A pointer to an array of *struct* *vm\_page* for CRYPTO\_BUF\_VMPAGE.

- *cb\_vm\_page\_len*

  The total amount of data included in the *cb\_vm\_page* array, in bytes.

- *cb\_vm\_page\_offset*

  Offset in bytes in the first page of *cb\_vm\_page* where valid data begins.

### Cursors

Cursors provide a mechanism for iterating over a data buffer. They are primarily intended for use in software drivers which access data buffers via virtual addresses.

**crypto\_cursor\_init**() initializes the cursor *cc* to reference the start of the data buffer *cb*.

**crypto\_cursor\_advance**() advances the cursor *amount* bytes forward in the data buffer.

**crypto\_cursor\_copyback**() copies *size* bytes from the local buffer pointed to by *src* into the data buffer associated with *cc*. The bytes are written to the current position of *cc*, and the cursor is then advanced by *size* bytes.

**crypto\_cursor\_copydata**() copies *size* bytes out of the data buffer associated with *cc* into a local buffer pointed to by *dst*. The bytes are read from the current position of *cc*, and the cursor is then advanced by *size* bytes.

**crypto\_cursor\_copydata\_noadv**() is similar to **crypto\_cursor\_copydata**() except that it does not change the current position of *cc*.

**crypto\_cursor\_segment**() returns the start of the virtually-contiguous segment at the current position of *cc*. The length of the segment is stored in *len*.

## RETURN VALUES

**crypto\_apply**() and **crypto\_apply\_buf**() return the return value from the caller-supplied callback function.

**crypto\_buffer\_contiguous\_subsegment**(), **crypto\_contiguous\_subsegment**(), and **crypto\_cursor\_segment**() return a pointer to a contiguous segment or NULL.

**crypto\_buffer\_len**() returns the length of a buffer in bytes.

**crypto\_cursor\_seglen**() returns the length in bytes of a contiguous segment.

**crypto\_cursor\_copy**() makes a deep copy of the cursor *fromc*. The two copies do not share any state and can thus be used independently.

**CRYPTO\_HAS\_OUTPUT\_BUFFER**() returns true if the request uses a separate output buffer.

## SEE ALSO

[ipsec(4)](/ipsec/4.md), [crypto(7)](/crypto/7.md), [bus\_dma(9)](/bus_dma/9.md), [crypto(9)](/crypto/9.md), [crypto\_driver(9)](/crypto_driver/9.md), [crypto\_request(9)](/crypto_request/9.md), [crypto\_session(9)](/crypto_session/9.md), [mbuf(9)](/mbuf/9.md), [uio(9)](/uio/9.md)

## HISTORY

The **crypto\_buffer** functions first appeared in FreeBSD 13.

## AUTHORS

The **crypto\_buffer** functions and this manual page were written by John Baldwin ⟨*jhb@FreeBSD.org*⟩.