---
name: "cpuset_getaffinity"
section: "2freebsd"
platform: "linux"
package: "freebsd-manpages"
version: "12.2-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/cpuset_getaffinity/2freebsd"
---

# cpuset\_getaffinity(2freebsd)

manage CPU affinity

## NAME

**cpuset\_getaffinity**, **cpuset\_setaffinity** – manage CPU affinity

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<sys/param.h\>**

**#include \<sys/cpuset.h\>**

*int*\

**cpuset\_getaffinity**(*cpulevel\_t level*, *cpuwhich\_t which*, *id\_t id*, *size\_t setsize*, *cpuset\_t \*mask*);

*int*\

**cpuset\_setaffinity**(*cpulevel\_t level*, *cpuwhich\_t which*, *id\_t id*, *size\_t setsize*, *const cpuset\_t \*mask*);

## DESCRIPTION

**cpuset\_getaffinity**() and **cpuset\_setaffinity**() allow the manipulation of sets of CPUs available to processes, threads, interrupts, jails and other resources. These functions may manipulate sets of CPUs that contain many processes or per-object anonymous masks that effect only a single object.

The valid values for the *level* and *which* arguments are documented in [cpuset(2)](/cpuset/2.md). These arguments specify which object and which set of the object we are referring to. Not all possible combinations are valid. For example, only processes may belong to a numbered set accessed by a *level* argument of CPU\_LEVEL\_CPUSET. All resources, however, have a mask which may be manipulated with CPU\_LEVEL\_WHICH.

Masks of type *cpuset\_t* are composed using the CPU\_SET macros. The kernel tolerates large sets as long as all CPUs specified in the set exist. Sets smaller than the kernel uses generate an error on calls to **cpuset\_getaffinity**() even if the result set would fit within the user supplied set. Calls to **cpuset\_setaffinity**() tolerate small sets with no restrictions.

The supplied mask should have a size of *setsize* bytes. This size is usually provided by calling sizeof(mask) which is ultimately determined by the value of CPU\_SETSIZE as defined in ⟨sys/cpuset.h⟩.

**cpuset\_getaffinity**() retrieves the mask from the object specified by *level*, *which* and *id* and stores it in the space provided by *mask*.

**cpuset\_setaffinity**() attempts to set the mask for the object specified by *level*, *which* and *id* to the value in *mask*.

## RETURN VALUES

The **cpuset\_getaffinity()** function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

## ERRORS

The following error codes may be set in *errno*:

- \[EINVAL\]

  The *level* or *which* argument was not a valid value.

- \[EINVAL\]

  The *mask* argument specified when calling **cpuset\_setaffinity**() was not a valid value.

- \[EDEADLK\]

  The **cpuset\_setaffinity**() call would leave a thread without a valid CPU to run on because the set does not overlap with the thread's anonymous mask.

- \[EFAULT\]

  The mask pointer passed was invalid.

- \[ESRCH\]

  The object specified by the *id* and *which* arguments could not be found.

- \[ERANGE\]

  The *cpusetsize* was either preposterously large or smaller than the kernel set size.

- \[EPERM\]

  The calling process did not have the credentials required to complete the operation.

- \[ECAPMODE\]

  The calling process attempted to act on a process other than itself, while  in capability mode. See [capsicum(4)](/capsicum/4.md).

## SEE ALSO

[capsicum(4)](/capsicum/4.md), [cpuset(1)](/cpuset/1.md), [cpuset(2)](/cpuset/2.md), [cpuset\_getid(2)](/cpuset_getid/2.md), [cpuset\_setid(2)](/cpuset_setid/2.md), [cpuset\_getdomain(2)](/cpuset_getdomain/2.md), [cpuset\_setdomain(2)](/cpuset_setdomain/2.md), [pthread\_affinity\_np(3)](/pthread_affinity_np/3.md), [pthread\_attr\_affinity\_np(3)](/pthread_attr_affinity_np/3.md), [cpuset(9)](/cpuset/9.md)

## HISTORY

The **cpuset\_getaffinity** family of system calls first appeared in FreeBSD 7.1.

## AUTHORS

Jeffrey Roberson ⟨*jeff@FreeBSD.org*⟩