mlock(3)						     Library Functions Manual							  mlock(3)

NAME

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

LIBRARY

       Realtime Library (librt.so, librt.a)

SYNOPSIS

       #include <sys/mman.h>

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

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

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 continu-
       ing 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 munlock 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  implemen-
		      tation-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.

RELATED INFORMATION

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

       Guide to Realtime Programming delim off

																	  mlock(3)