msync(3C) Standard C Library Functions msync(3C)NAMEmsync - 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.
· All write references to the memory region made prior to the call
are visible by subsequent read operations on the file.
· 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.
· 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.
· All writes to the mapped portion of the file made prior to the
call are visible by subsequent read references to the mapped mem‐
ory region.
· 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. There‐
fore, there are no guarantees that msync() is the only control over
when pages are or are not written to disk.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Standard │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │MT-Safe │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOmemcntl(2), mmap(2), sysconf(3C), attributes(5), standards(5)SunOS 5.10 24 Jul 2002 msync(3C)
