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

NAME
     msync - synchronize a mapped region



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

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

DESCRIPTION
     The msync() system call writes all pages with shared modifications in the
     specified region of the process's address space back to permanent stor-
     age, 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 opera-
     tions 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
     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
     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 al-
                   lowed for the address space of the process, or specify one
                   or more pages which are unmapped.

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

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

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

HISTORY
     The msync() function first appeared in 4.4BSD. It was modified to conform
     to IEEE Std1003.1b-1993 (``POSIX'')

OpenBSD 2.6                    October 10, 1997                              1