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msync() - Unix, Linux System Call
msync - synchronize a file with a memory map
int msync(void *start, size_t length, int flags);
msync() flushes changes made to the in-core copy of a file that was mapped
into memory using
back to disk. Without use of this call
there is no guarantee that changes are written back before
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
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).
On success, zero is returned. On error, -1 is returned, and
errno is set appropriately.
start is not a multiple of PAGESIZE; or any bit other than
MS_ASYNC | MS_INVALIDATE | MS_SYNC is set in
flags; or both
MS_SYNC and MS_ASYNC are set in
The indicated memory (or part of it) was not mapped.
On POSIX systems on which
msync() is available, both
_POSIX_SYNCHRONIZED_IO are defined in <unistd.h> to a value greater than 0. (See also
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.
B.O. Gallmeister, POSIX.4, OReilly, pp. 128-129 and 389-391.