msync
NAME
msync - synchronize a file with a memory map
SYNOPSIS
#include <sys/mman.h>
I int msync(void * start , size_t length , int flags );
DESCRIPTION
R 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
R MS_ASYNC ,
R MS_SYNC ,
and
MS_INVALIDATE
set, but not both
MS_ASYNC
and
R 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
R EBUSY
MS_INVALIDATE
was specified in
R flags ,
and a memory lock exists for the specified address range.
R EINVAL
start
is not a multiple of PAGESIZE; or any bit other than
R MS_ASYNC | MS_INVALIDATE | MS_SYNC
is set in
R flags ;
or both
MS_SYNC
and
MS_ASYNC
are set in
R flags .
ENOMEM
The indicated memory (or part of it) was not mapped.
CONFORMING TO
POSIX.1-2001.
This call was introduced in Linux 1.3.21, and then used
EFAULT
instead of
R ENOMEM .
In Linux 2.4.19 this was changed to the POSIX value
R ENOMEM .
AVAILABILITY
On POSIX systems on which
R 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).)
SEE ALSO
mmap(2)
B.O. Gallmeister, POSIX.4, O'Reilly, pp. 128-129 and 389-391.
B.O. Gallmeister, POSIX.4, O'Reilly, pp. 128-129 and 389-391.
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