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mlock(3)
NAME
  mlock, munlock - Locks or unlocks a specified region in memory (P1003.1b)

SYNOPSIS
  #include <sys/mman.h>

  int mlock (
  const void *addr,
  size_t len);

  int munlock (
  const void *addr,
  size_t len);

LIBRARY
  Realtime Library (librt.so, librt.a)

PARAMETERS
  *addr
      A pointer to the starting address of the region to lock or unlock. The
      addr argument must be a multiple of the page size returned by the
      sysconf system call.

  len The size of the memory region to lock or unlock. The value of len is
      rounded up to a multiple of the page size before decrementing by 1.

DESCRIPTION
  The mlock and munlock functions lock and unlock whole pages containing any
  part of the process address space starting at addr and continuing for len
  bytes.

  The mlock function guarantees all whole pages mapped by the range addr to
  addr+len-1 (inclusive) to be memory resident. (The area locked is the same
  as if the len argument were rounded up to a multiple of the page size
  before decrementing by 1.)

  The locked area remains locked until unlocked with a call to the munlock
  function, until the process calls the exec function, until an address space
  associated with the lock is unmapped, or until the process terminates. A
  lock is not inherited across a fork or an exec.

  The mlock function unlocks whole pages previously mapped by the range addr
  to addr+len-1 (inclusive), regardless of how many times the mlock function
  was called by the process for any pages within the specified range.

  A call to the munlock function does not affect pages that may be mapped
  into another process's address space or locked by another process.

  You must have superuser privileges to call the mlock or munlock  functions.

RETURN VALUES
  On a successful call to the mlock function, a value of 0 (zero) is returned
  and the region becomes locked and memory resident.  On an unsuccessful
  call, a value of -1 is returned, no changes are made to any locks in the
  process address space, and errno is set to indicate that an error occurred.

  On a successful call to the munlock function, a value of 0 (zero) is
  returned and the memory is unlocked with respect to the process's address
  space. On an unsuccessful call, a value of -1 is returned, none of the
  memory is unlocked, and errno is set to indicate that an error occurred.

ERRORS
  The mlock and munlock functions fail under the following conditions:

  [EINVAL]
      The addr argument is not a multiple of the page size returned by
      sysconf.

  [ENOMEM]
      Some or all of the address range specified by the addr and len
      arguments does not correspond to valid mapped pages in the process's
      address space. For the mlock function, locking the pages mapped by the
      specified range would exceed an implementation-defined limit on the
      amount of memory that the process may lock.

  If any of the following conditions occur, the mlock function fails:

  [EAGAIN]
      Some or all of the memory identified by the operation could not be
      locked when the call was made.

  [EPERM]
      The calling process does not have the appropriate privileges to perform
      the requested operation.

SEE ALSO
  Functions: exec(2), _exit(2), fork(2), munmap(2), sysconf(3)

  Guide to Realtime Programming

Index for Section 3

Alphabetical listing for M

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