mlockall(3P4)                                       mlockall(3P4)



NAME
     mlockall, munlockall - POSIX 1003.4 Process Memory Locking

SYNOPSIS
     #include <sys/mman.h>

     int mlockall(flags)

          int flags

     int munlockall(void)

DESCRIPTION
     The mlockall() function causes all of the process' virtual
     address space to be memory resident until unlocked, or until
     the process exits or execs another process image.  The flags
     argument determines whether the space to be locked would be
     limited to the process' current virtual address space or the
     process' current virtual address space plus any future
     expansion.  Flags is constructed from the OR of one or more
     of the following symbolic constants, defined in
     <sys/mman.h>:
        MCL_CURRENT    Lock all of the process' virtual address
                       space, not including subsequent expansion
                       of this space.

        MCL_FUTURE     Lock all new virtual pages added to the
                       process' virtual address space after the
                       call to mlockall().

     MCL_CURRENT must be specified.

     If MCL_FUTURE is specified:

        If the automatic locking of future mappings causes the
        minimum number of real memory pages in global memory
        available to the kernel to fall below a system limit, the
        new mappings are not locked and the process is notified.
        Each page in global memory that is locked causes the
        number of real memory pages available to the kernel to
        decrease.

        If the new mapping is due to the growth of the stack
        region then error notification consists of a SIGSEGV sig-
        nal being sent to the process.  A process' user stack is
        automatically extended when the process accesses a loca-
        tion beyond the the current end of the stack region, but
        within the extendable stack space.

        If the new mapping is due to the growth of the data
        region or to the allocation of a shared memory segment
        region, then error notification is handled by the system



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mlockall(3P4)                                       mlockall(3P4)



        call the process made to get the new mapping, e.g. sbrk()
        and shmat().

     The munlockall() function unlocks all of the process' vir-
     tual address space.  Any pages that become mapped into the
     process's address space after a call to munlockall() are not
     locked, unless there is an intervening call to mlockall().
     If pages mapped into the process's address space are also
     mapped into other process's address spaces and are locked by
     those processes, the locks established by the other
     processes are unaffected by this process's call to munlock-
     all().

     Locks are not nested. The process address space may be
     locked several times with mlockall() but will be unlocked by
     a single call to munlockall().

     Per-process memory locks are not inherited across a fork(),
     and all memory locks owned by a process are unlocked upon
     exec() or process termination.

     To use both of these library calls, the caller must either
     be a superuser or have the ACC_PLOCK bit set in its access
     vector.

     These interfaces should not be used to lock memory regions
     which will be used for direct I/O. See userdma(2) for an
     interface that can be used for this purpose.

RETURN VALUE
     Upon successful completion, the mlockall() function returns
     a value of zero.  Otherwise, no memory is locked, a value of
     -1 is returned and errno is set to indicate the error.

     The munlockall() function always returns a value of zero.

     If any of the following conditions occur, the mlockall()
     function returns -1 and sets errno to the corresponding
     value:

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

     [EINVAL]       The flags argument is zero, or includes unim-
                    plemented flags.  MCL_CURRENT and
                    MCL_CURRENT|MCL_FUTURE are supported.
                    MCL_FUTURE is not supported.

     [EPERM]        The effective user ID of the calling process
                    is not super-user or the user does not have
                    the ACC_PLOCK access vector (If access



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mlockall(3P4)                                       mlockall(3P4)



                    vectors are configured).

FILES
     /usr/lib/libposix4.a

SEE ALSO
     mlock(3P4), fork(2), exec(2), exit(2).

BUGS
     The current implementation requires the user to specify
     MCL_CURRENT. Specifying MCL_FUTURE by itself is illegal.

     A call to mlockall() with only the MCL_CURRENT flag speci-
     fied is supported with a slight variation from the implemen-
     tation specified by POSIX 1003.4.  When MCL_CURRENT is
     specified, all pages in the regions currently held by a pro-
     cess are locked. Pages allocated in the future to those
     regions are implicitly locked. Regions which are subse-
     quently added to the process' address space are not locked.

WARNING
     The interfaces to mlockall() and munlockall() are based on
     IEEE Draft Standard P1003.4/D12.  This is an unapproved
     draft, subject to change.  Use of information contained in
     this unapproved draft is at your own risk.  This interface
     will change to reflect any changes made by future drafts of
     POSIX 1003.4.




























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