msync(2) - NetBSD Manual Pages

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


NAME

     msync - synchronize a mapped region


SYNOPSIS

     #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
     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 ex-
     cept 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.


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.

     [EINVAL]      The addr parameter did not specify an address part of a
                   mapped region.

     [EINVAL]      The len parameter was negative.

     [EIO]         An I/O error occured while writing to the file system.

     [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.


SEE ALSO

     mlock(2), mmap(2), munlock(2)


BUGS

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


HISTORY

     The msync() function first appeared in 4.4BSD.  It was modified to con-
     form to IEEE Std1003.1b-1993 (``POSIX'') in NetBSD 1.3.

NetBSD 1.4                     October 10, 1997                              1