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MLOCK(3P)                  POSIX Programmer's Manual                 MLOCK(3P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
NAME
       mlock, munlock - lock or unlock a range of process address space (REAL-
       TIME)
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  con-
       tinuing 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 vol-
       ume 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 .

IEEE/The Open Group                  2003                            MLOCK(3P)