msync(2) -- Linux man page
NAME
msync - synchronize a file with a memory map
SYNOPSIS
#include <sys/mman.h>
int msync(void *start, size_t length, int flags);
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.
- ENOMEM
-
The indicated memory (or part of it) was not mapped.
AVAILABILITY
On POSIX systems on which
msync
is available, both
_POSIX_MAPPED_FILES
and
_POSIX_SYNCHRONIZED_IO
are defined in <unistd.h> to a value greater than 0. (See also
sysconf(3).)
CONFORMING TO
POSIX.1b (formerly POSIX.4)
This call was introduced in Linux 1.3.21, and then used EFAULT instead of
ENOMEM. In Linux 2.4.19 this was changed to the POSIX value ENOMEM.
SEE ALSO
mmap(2),
B.O. Gallmeister, POSIX.4, O'Reilly, pp. 128-129 and 389-391.
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