NAME

mlock, munlock − lock / unlock a range of process memory

SYNOPSIS

#include <sys/mman.h>

int mlock(addr, len)

caddr_t ∗addr

size_t len

int munlock(addr, len)

caddr_t ∗addr

size_t len

DESCRIPTION

The function mlock causes all of the pages mapped by the range addr to addr + len
 - 1 inclusive to be memory resident until unlocked, or until the process exits or execs another process image.  The argument addr has to be a multiple of the page size returned by sysconf(2).  The area locked is a multiple of the system page size such that it contains the specified address range. 

The function munlock unlocks all of the pages mapped by the range addr to addr + len
 - 1 inclusive. The area unlocked is a multiple of the system page size such that it contains the specified address range. Locks are nested, hence, the number of munlock calls required to unlock the address range is the same as the number of mlock calls made on that address range. 

Upon successful return from mlock, pages encompassing the specified range are locked and are memory resident. Upon successful return from munlock, the lock counts of the pages encompassing the specified range are decremented. 

Per-process memory locks for ranges of pages are not inherited across a fork, and all memory locks owned by a process are unlocked upon exec(2) or process termination. 

To use both of these library calls, the caller must either be a superuser or have the ACC_PLOCK bit set in its access vector. 

These interfaces should not be used to lock memory regions which will be used for direct I/O. See userdma(2) for an interface that can be used for this purpose. 

RETURN VALUE

Upon successful completion, the mlock and munlock functions return a value of zero.  Otherwise, a value of -1 is returned and errno is set to indicate the error. 

If any of the following conditions occur, the mlock and munlock functions return -1 and set errno to the corresponding value:

[EINVAL] The addr argument is not a multiple of the page size returned by sysconf(2). 

[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. 

If any of the following conditions occur, the mlock function shall return -1 and set errno to the corresponding value:

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

[EPERM] The effective user ID of the calling process is not super-user or the user does not have the ACC_PLOCK access vector (If access vectors are configured). 

FILES

/usr/lib/libposix4.a

SEE ALSO

mlockall(3P4), fork(2), exec(2), exit(2). 

BUGS

If any of the pages in the range specified to a call to munlock are also mapped into another process’ address spaces, locks established on those pages by another process may be affected by this process’s call to munlock.  munlock decrements the lock count on a page even when the current process was not the one that originally locked the page in memory. 

WARNING

The interfaces to mlock and munlock are based on IEEE Draft Standard P1003.4/D12.  This is an unapproved draft, subject to change.  Use of information contained in this unapproved draft is at your own risk.  This interface will change to reflect any changes made by future drafts of POSIX 1003.4. 

CX/UX Programmer’s Reference Manual