redhat man page for msync

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

NAME
       msync - synchronize a file with a memory map

SYNOPSIS
       #include <unistd.h>
       #include <sys/mman.h>

       #ifdef _POSIX_MAPPED_FILES
       #ifdef _POSIX_SYNCHRONIZED_IO

       int msync(const void *start, size_t length, int flags);

       #endif
       #endif

DESCRIPTION
       msync  flushes changes made to the in-core copy of a file that was mapped into memory using mmap(2) back to disk.  Without use of this call
       there is no guarantee that changes are written back before munmap(2) is called.	To be more precise, the part of the file that  corresponds
       to  the	memory	area  starting	at  start and having length length is updated.	The flags argument may have the bits MS_ASYNC, MS_SYNC and
       MS_INVALIDATE set, but not both MS_ASYNC and MS_SYNC.  MS_ASYNC specifies that an update be scheduled, but the  call  returns  immediately.
       MS_SYNC	asks  for  an update and waits for it to complete.  MS_INVALIDATE asks to invalidate other mappings of the same file (so that they
       can be updated with the fresh values just written).

RETURN VALUE
       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

ERRORS
       EINVAL start is not a multiple of PAGESIZE, or any bit other than MS_ASYNC | MS_INVALIDATE | MS_SYNC is set in flags.

       EFAULT The indicated memory (or part of it) was not mapped.

CONFORMING TO
       POSIX.1b (formerly POSIX.4)

SEE ALSO
       mmap(2), B.O. Gallmeister, POSIX.4, O'Reilly, pp. 128-129 and 389-391.

Linux 1.3.86							    1996-04-12								  MSYNC(2)