NAME    [Toc]    [Back]

       msync - synchronize a file with a memory map

SYNOPSIS    [Toc]    [Back]

       #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    [Toc]    [Back]

       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 mun-
       map(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    [Toc]    [Back]

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

ERRORS    [Toc]    [Back]

       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    [Toc]    [Back]

       POSIX.1b (formerly POSIX.4)

SEE ALSO    [Toc]    [Back]

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



Linux 1.3.86			  1996-04-12			      MSYNC(2)