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_ASYNCSpecifies that an update be scheduled, but the call returns immediately.
MS_SYNCRequests an update and waits for it to complete.
MS_INVALIDATEAsks 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.
MS_INVALIDATE was
specified in flags, and a memory lock
exists for the specified address range.
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.
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.
This page is part of release 4.07 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/.
|
Copyright (C) 1996 Andries Brouwer (aebcwi.nl) %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END |