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 (con-
       sult 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 (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 pro-
       cesses, 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 indi-
       cate 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 mem-
              ory 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,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                     MLOCK(3P)