mlock(3)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
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. 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 func‐
tions.
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:
The addr argument is not a multiple of the page size returned by
sysconf. 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:
Some or all of the memory identified by the operation could not be
locked when the call was made. 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
mlock(3)
