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 .