Standards
| Standards / Extensions |
C or C++ |
Dependencies |
|---|
XPG4.2
Single UNIX Specification, Version 3
|
both |
|
Format
#define _XOPEN_SOURCE_EXTENDED 1
#include <sys/mman.h>
int msync(void *addr, size_t len, int flags);
General 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
flags argument is:
- MS_ASYNC
- Perform asynchronous writes
- MS_INVALIDATE
- Invalidate mappings
- MS_SYNC
- Perform synchronous writes
The function synchronizes the file contents
to match the current contents to the memory region.
- All write references to the memory region made before the call
are visible by subsequent read operations on the file.
- It is unspecified whether writes to the same portion of the file
before the call are visible by read references to the memory region.
- It is unspecified whether unmodified pages in the specified range
are also written to the underlying hardware.
If flags is MS_ASYNC, the function
may return immediately once all write operations are schedule; if flags is
MS_SYNC, the function does not return until all write operations are
completed.
MS_INVALIDATE synchronizes the contents of the memory
region to match the current file contents.
- All writes to the mapped portion of the file made before the call
are visible by subsequent read references to the mapped memory region.
- It is unspecified whether write references before 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.
Returned value
If successful, msync() returns
0.
If unsuccessful, msync() returns -1 and sets errno to one
of the following values:
- Error Code
- Description
- EINVAL
- The addr argument is not a multiple
of the page size as returned by sysnonf.
- EIO
- An I/O error occurred while reading from or writing to the file
system.
- ENOMEM
- Some or all the addresses in the range [addr, addr +
range [addr, addr + len)
are len) are invalid for the address space
of the process or pages not mapped are specified.