|
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
|
|
|
MSYNC(2) Linux Programmer's Manual MSYNC(2)
msync - synchronize a file with a memory map
#include <sys/mman.h>
int msync(void *addr, size_t length, int flags);
msync() flushes changes made to the in-core copy of a file that
was mapped into memory using mmap(2) back to the filesystem.
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
addr and having length length is updated.
The flags argument should specify exactly one of MS_ASYNC and
MS_SYNC, and may additionally include the MS_INVALIDATE bit.
These bits have the following meanings:
MS_ASYNC
Specifies that an update be scheduled, but the call
returns immediately.
MS_SYNC
Requests 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.
EBUSY MS_INVALIDATE was specified in flags, and a memory lock
exists for the specified address range.
EINVAL addr 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 flags.
ENOMEM The indicated memory (or part of it) was not mapped.
POSIX.1-2001, POSIX.1-2008.
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.
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).)
According to POSIX, either MS_SYNC or MS_ASYNC must be specified
in flags, and indeed failure to include one of these flags will
cause msync() to fail on some systems. However, Linux permits a
call to msync() that specifies neither of these flags, with
semantics that are (currently) equivalent to specifying MS_ASYNC.
(Since Linux 2.6.19, MS_ASYNC is in fact a no-op, since the
kernel properly tracks dirty pages and flushes them to storage as
necessary.) Notwithstanding the Linux behavior, portable,
future-proof applications should ensure that they specify either
MS_SYNC or MS_ASYNC in flags.
mmap(2)
B.O. Gallmeister, POSIX.4, O'Reilly, pp. 128–129 and 389–391.
This page is part of release 5.10 of the Linux man-pages project.
A description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2020-06-09 MSYNC(2)
Pages that refer to this page: madvise(2), mmap2(2), mmap(2), remap_file_pages(2), sync_file_range(2), syscalls(2), nfs(5), systemd.exec(5), fanotify(7), inotify(7), xfs_io(8)
Copyright and license for this manual page
|
HTML rendering created 2020-12-21 by Michael Kerrisk, author of The Linux Programming Interface, maintainer of the Linux man-pages project. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|