msync(2)

1MSYNC(2)                   Linux Programmer's Manual                  MSYNC(2)
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NAME

6       msync - synchronize a file with a memory map
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SYNOPSIS

9       #include <sys/mman.h>
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11       int msync(void *start, size_t length, int flags);
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DESCRIPTION

14       msync()  flushes  changes  made  to the in-core copy of a file that was
15       mapped into memory using mmap(2) back to disk.   Without  use  of  this
16       call  there  is  no guarantee that changes are written back before mun‐
17       map(2) is called.  To be more precise, the part of the file that corre‐
18       sponds to the memory area starting at start and having length length is
19       updated.
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21       The flags argument may have the bits MS_ASYNC, MS_SYNC, and  MS_INVALI‐
22       DATE  set,  but not both MS_ASYNC and MS_SYNC.  MS_ASYNC specifies that
23       an update be scheduled, but the call returns immediately.  MS_SYNC asks
24       for  an  update  and  waits  for it to complete.  MS_INVALIDATE asks to
25       invalidate other mappings of the same file (so that they can be updated
26       with the fresh values just written).
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RETURN VALUE

29       On  success,  zero is returned.  On error, -1 is returned, and errno is
30       set appropriately.
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ERRORS

33       EBUSY  MS_INVALIDATE was specified in flags, and a memory  lock  exists
34              for the specified address range.
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36       EINVAL start  is  not  a  multiple  of  PAGESIZE; or any bit other than
37              MS_ASYNC | MS_INVALIDATE | MS_SYNC is  set  in  flags;  or  both
38              MS_SYNC and MS_ASYNC are set in flags.
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40       ENOMEM The indicated memory (or part of it) was not mapped.
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AVAILABILITY

43       On    POSIX    systems    on   which   msync()   is   available,   both
44       _POSIX_MAPPED_FILES   and   _POSIX_SYNCHRONIZED_IO   are   defined   in
45       <unistd.h> to a value greater than 0. (See also sysconf(3).)
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CONFORMING TO

48       POSIX.1-2001.
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50       This  call was introduced in Linux 1.3.21, and then used EFAULT instead
51       of ENOMEM. In Linux 2.4.19 this was changed to the POSIX value ENOMEM.
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