NAME

mlock, munlock - lock or unlock a range of process address space (REALTIME)

 SYNOPSIS

#include <sys/mman.h>

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

 DESCRIPTION

The function mlock() causes those whole pages containing any part of the address space of the process starting at address addr and continuing for len bytes to be memory resident until unlocked or until the process exits or execs another process image. The implementation may require that addr be a multiple of {PAGESIZE}.

The function munlock() unlocks those whole pages containing any part of the address space of the process starting at address addr and continuing for len bytes, regardless of how many times mlock() has been called by the process for any of the pages in the specified range. The implementation may require that addr be a multiple of the {PAGESIZE}.

If any of the pages in the range specified to a call to munlock() are also mapped into the address spaces of other processes, any locks established on those pages by another process are unaffected by the call of this process to munlock(). If any of the pages in the range specified by a call to munlock() are also mapped into other portions of the address space of the calling process outside the range specified, any locks established on those pages via the other mappings are also unaffected by this call.

Upon successful return from mlock(), pages in the specified range will be locked and memory resident. Upon successful return from munlock(), pages in the specified range will be unlocked with respect to the address space of the process. Memory residency of unlocked pages is unspecified.

The appropriate privilege is required to lock process memory with mlock().

 RETURN VALUE

Upon successful completion, the mlock() and munlock() functions return a value of zero. Otherwise, no change is made to any locks in the address space of the process, and the function returns a value of -1 and sets errno to indicate the error.

 ERRORS

The mlock() and munlock() functions will fail if:

[ENOMEM]

Some or all of the address range specified by the addr and len arguments does not correspond to valid mapped pages in the address space of the process.

[ENOSYS]

The implementation does not support this memory locking interface.

The mlock() functions will fail if:

[EAGAIN]

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

The mlock() and munlock() functions may fail if:

[EINVAL]

The addr argument is not a multiple of {PAGESIZE}.

The mlock() function may fail if:

[ENOMEM]

Locking the pages mapped by the specified range would exceed an implementation-dependent limit on the amount of memory that the process may lock.

[EPERM]

The calling process does not have the appropriate privilege to perform the requested operation.

 EXAMPLES

None.

 APPLICATION USAGE

None.

 SEE ALSO

exec, _exit(), fork(), mlockall(), munmap(), <sys/mman.h>.

DERIVATION

Derived from the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995)