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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 mlock() function shall cause 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 munlock() function shall unlock 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 {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 shall
       be locked and memory-resident. Upon successful return  from  munlock(),
       pages  in  the  specified  range  shall 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  shall
       return  a  value  of zero. Otherwise, no change is made to any locks in
       the address space of the process, and the function shall return a value
       of -1 and set errno to indicate the error.

ERRORS

       The mlock() and munlock() functions shall 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.

       The mlock() function shall 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-defined  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.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       exec() , exit() , fork() , mlockall() , munmap() , the Base Definitions
       volume of IEEE Std 1003.1-2001, <sys/mman.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
       event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard
       is  the  referee document. The original Standard can be obtained online
       at http://www.opengroup.org/unix/online.html .