NAME    [Toc]    [Back]

     msync - synchronize a mapped region

SYNOPSIS    [Toc]    [Back]

     #include <sys/types.h>
     #include <sys/mman.h>

     int
     msync(void *addr, size_t len, int flags);

DESCRIPTION    [Toc]    [Back]

     The msync() system call writes all pages with shared modifications in the
     specified region of the process's address space back to permanent storage,
 and, if requested, invalidates cached  data  mapped  in
the region.  If
     len  is  0,  all modified pages within the region containing
addr will be
     flushed; if len is non-zero, only modified pages  containing
addr and
     len-1  succeeding  locations  will be flushed.  Any required
synchronization
     of  memory  caches  will  also  take  place  at  this  time.
Filesystem operations
  on a file that is mapped for shared modifications are
unpredictable
     except after an msync().

     The flags argument is formed by OR'ing the following values

           MS_ASYNC        Perform asynchronous writes.
           MS_SYNC         Perform synchronous writes.
           MS_INVALIDATE   Invalidate cached data after  writing.

RETURN VALUES    [Toc]    [Back]

     Upon  successful completion, a value of 0 is returned.  Otherwise, a value
     of -1 is returned and errno is set to indicate the error.

ERRORS    [Toc]    [Back]

     The following errors may be reported:

     [EBUSY]       The MS_INVALIDATE flag  was  specified  and  a
portion of the
                   specified region was locked with mlock(2).

     [EINVAL]      The specified flags argument was invalid.

     [EINVAL]      The addr parameter was not page aligned.

     [ENOMEM]       Addresses in the specified region are outside
the range allowed
 for the address space of the process, or
specify one
                   or more pages which are unmapped.

     [EIO]         An I/O error occurred while writing.

SEE ALSO    [Toc]    [Back]

     madvise(2), mincore(2), minherit(2), mprotect(2), munmap(2)

HISTORY    [Toc]    [Back]

     The msync() function first appeared in 4.4BSD.  It was modified to conform
 to IEEE Std 1003.1b-1993 (``POSIX'')

BUGS    [Toc]    [Back]

     Writes are currently done synchronously even if the MS_ASYNC
flag is
     specified.

OpenBSD      3.6                         October     10,     1997