memcntl(2)                                                   memcntl(2)

  memcntl()

    memcntl - manage memory in mappings

  SYNOPSIS

    #include 

    int memcntl(void *addr, size_t len, int cmd,
                void *arg, int attr, int mask)

  DESCRIPTION

    The memcntl(2) call controls and manages a mapped address space in the
    range [addr addr + len]. The attr argument selects the pages to be
    affected; it contains a bit pattern of page attributes which are ORed
    together.

    Page mapping

    SHARED         Page is mapped shared

    PRIVATE        Page is mapped private

    Page protection

    PROT_READ      Page is readable

    PROT_WRITE     Page is writeable

    PROT_EXEC      Page is executable

    Process criteria

    PROC_DATA      Process data: write permission for privately-mapped
                   segments

    PROC_TEXT      Process text: read and execute permission for
                   privately-mapped segments

    The cmd argument specifies the actual operation. The arg argument may
    modify the actual command, and is usually a bit pattern ORed together. The
    file  defines these operations:

    MC_LOCK
        Lock the pages in the range that have the specified attributes.
        Although different mappings may cause the same page to be locked more
        than once, the locks do not nest within a particular mapping. One
        unlock operation undoes all the locks held on a page by a process, but
        locks held by aanother process are held in memory until the locking
        process has released the lock. (If a locked page is removed or
        deleted, that implicitly unlocks it.)
        The value of arg must be 0.

    MC_LOCKAS
        Lock the pages in the address space that have the specified
        attributes. In this case, the arg value controls whether the locked
        pages are mapped in the current address space or ones that will be
        mapped later, or both.

    The addr value must be NULL and the len value must be 0.

    Values that can be ORed into arg are:

    MCL_CURRENT
        Lock the current mappings

    MCL_FUTURE
        Lock all mappings added to the address space, so long as there is
        sufficient memory

    MC_UNLOCK
        Unlock all of the pages in the range that have the specified
        attributes. The value of arg must be 0.

    MC_UNLOCKAS
        Unlock any locks on the address space (MC_LOCKAS) and remove locks on
        all pages in the address space that have the specified attributes.

    The mask argument is reserved for future use and must be set to 0.

  RETURN VALUES

    The memcntl(2) utility exits with status 0 for success, and -1 if an error
    occurred.

  ERRORS

    The memcntl(2) function can fail for the following reasons:

    [EAGAIN]
        Insufficient resources to lock some or all of the memory.

    [EBUSY]
        One of the pages is locked in memory and MS_INVALIDATE was the
        command.

    [EINVAL]
        The addr is invalid. It must be a multiple of the page size. If the
        command is MC_LOCKAS or MC_UNLOCKAS, the value of addr is not NULL, or
        the value of len is not zero. It may also mean the value of arg was
        not correct for the command given.

    [EIO]
        An I/O error occurred.

    [ENOMEM]
        The addresses in the range are not valid for the address space of the
        process, or are for pages that aren't mapped.

    [EPERM]
        A locking command was specified and the effective user ID does not
        have appropriate privileges.

  SEE ALSO

    fork(2)

    mmap(2)

    mctl(3)

    msync(3)

    sysconf(2)

  USAGE NOTES

    The memcntl function is thread safe.

    The memcntl function is not async-signal safe.