MSYNC(3C) Standard C Library Functions MSYNC(3C)
NAME
msync - synchronize memory with physical storage
SYNOPSIS
#include <sys/mman.h>
int msync(
void *addr,
size_t len,
int flags);
DESCRIPTION
The
msync() function writes all modified copies of pages over the range
[
addr, addr + len) to the underlying hardware, or invalidates any copies
so that further references to the pages will be obtained by the system
from their permanent storage locations. The permanent storage for a
modified
MAP_SHARED mapping is the file the page is mapped to; the
permanent storage for a modified
MAP_PRIVATE mapping is its swap area.
The
flags argument is a bit pattern built from the following values:
MS_ASYNC perform asynchronous writes
MS_SYNC perform synchronous writes
MS_INVALIDATE invalidate mappings
If
flags is
MS_ASYNC or
MS_SYNC, the function synchronizes the file
contents to match the current contents of the memory region.
o All write references to the memory region made prior to the
call are visible by subsequent read operations on the file.
o All writes to the same portion of the file prior to the call
may or may not be visible by read references to the memory
region.
o Unmodified pages in the specified range are not written to the
underlying hardware.
If
flags is
MS_ASYNC, the function may return immediately once all write
operations are scheduled; if
flags is
MS_SYNC, the function does not
return until all write operations are completed.
If
flags is
MS_INVALIDATE, the function synchronizes the contents of the
memory region to match the current file contents.
o All writes to the mapped portion of the file made prior to the
call are visible by subsequent read references to the mapped
memory region.
o All write references prior to the call, by any process, to
memory regions mapped to the same portion of the file using
MAP_SHARED, are visible by read references to the region.
If
msync() causes any write to the file, then the file's
st_ctime and
st_mtime fields are marked for update.
RETURN VALUES
Upon successful completion,
msync() returns
0; otherwise, it returns
-1 and sets
errno to indicate the error.
ERRORS
The
msync() function will fail if:
EBUSY Some or all of the addresses in the range [
addr,
addr +
len)
are locked and
MS_SYNC with the
MS_INVALIDATE option is
specified.
EAGAIN Some or all pages in the range [
addr,
addr +
len) are locked
for I/O.
EINVAL The
addr argument is not a multiple of the page size as
returned by
sysconf(3C).
The
flags argument is not some combination of
MS_ASYNC and
MS_INVALIDATE.
EIO An I/O error occurred while reading from or writing to the file
system.
ENOMEM Addresses in the range [
addr, addr + len) are outside the valid
range for the address space of a process, or specify one or
more pages that are not mapped.
EPERM MS_INVALIDATE was specified and one or more of the pages is
locked in memory.
USAGE
The
msync() function should be used by programs that require a memory
object to be in a known state, for example in building transaction
facilities.
Normal system activity can cause pages to be written to disk. Therefore,
there are no guarantees that
msync() is the only control over when pages
are or are not written to disk.
ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+
SEE ALSO
memcntl(2),
mmap(2),
sysconf(3C),
attributes(7),
standards(7) July 24, 2002
MSYNC(3C)