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     cpuset_getaffinity, cpuset_setaffinity — manage CPU affinity


     Standard C Library (libc, -lc)


     #include <sys/param.h>
     #include <sys/cpuset.h>

     cpuset_getaffinity(cpulevel_t level, cpuwhich_t which, id_t id,
         size_t setsize, cpuset_t *mask);

     cpuset_setaffinity(cpulevel_t level, cpuwhich_t which, id_t id,
         size_t setsize, const cpuset_t *mask);


     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).  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(2) 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

     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.


     Upon successful completion, the value 0 is returned; otherwise the
     value -1 is returned and the global variable errno is set to indicate the


     The following error codes may be set in errno:

     [EINVAL]           The level or which argument 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.


     cpuset(1), cpuset(2), cpuset_getid(2), cpuset_setid(2), CPU_SET(3),
     pthread_affinity_np(3), pthread_attr_affinity_np(3)


     The cpuset_getaffinity family of system calls first appeared in
     FreeBSD 7.1.


     Jeffrey Roberson ⟨