View Source: mlock(2) - Waikato Linux Users Group

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!!NAME
mlock - disable paging for some parts of memory
!!SYNOPSIS
 #include <sys/mman.h>

 __int mlock(const void *__''addr''__, size_t __''len''__);__

!!DESCRIPTION
mlock(2) disables paging for the memory in the range starting at ''addr'' with length ''len'' bytes. All pages which contain a part of the specified memory range are
guaranteed be resident in RAM when the mlock(2) system call returns successfully and they are guaranteed to stay in RAM until the pages are unlocked by munlock(2) or
munlockall(2), or until the process terminates or starts another program with exec(2). Child processes do not inherit page locks across a fork(2).

Memory locking has two main applications: real-time algorithms and high-security data processing. Real-time applications require deterministic timing, and, like
scheduling, paging is one major cause of unexpected program execution delays. Real-time applications will usually also switch to a real-time scheduler with
__sched_setscheduler__. Cryptographic security software often handles critical bytes like passwords or secret keys as data structures. As a result of paging, these secrets could be transfered onto a persistent swap store medium, where they might be accessible to the enemy long after the security software has erased the secrets in RAM and terminated.

Memory locks do not stack, i.e., pages which have been locked several times by calls to mlock(2) or mlockall(2) will be unlocked by a single call to munlock(2) for the corresponding range or by munlockall(2). Pages which are mapped to several locations or by several processes stay locked into RAM as long as they are locked at least at one location or by at least one process.

On POSIX systems on which mlock and munlock are available,  ___POSIX_MEMLOCK_RANGE__  is  defined in <unistd.h> and the value PAGESIZE from <limits.h> indicates the number of bytes per page.


!!RETURN VALUE
On success, mlock(2) returns zero. On error, -1 is returned, ''errno'' is set appropriately, and no changes are made to any locks in the address space of the
process.

!!ERRORS
;[ENOMEM]: Some of the specified address range does not correspond to mapped pages in the address space of the process or the process tried to exceed the maximum number of allowed locked pages.
;[EPERM]: The calling process does not have appropriate privileges. Only root processes are allowed to lock pages.
;[EINVAL]: ''len'' was not a positive number.

!!CONFORMING TO

POSIX.1b, SVr4. SVr4 documents an additional [EAGAIN] error code.

!!SEE ALSO
munlock(2), mlockall(2), munlockall(2)

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Last edited on Monday, March 10, 2003 8:07:10 pm by PerryLorier

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