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Name

msync - synchronize memory with physical storage

Synopsis


#include <sys/types.h>
#include <sys/mman.h>

int msync(caddr_t addr, size_t len, int flags);

MT-Level

MT-Safe

Description

The function msync() writes all modified copies of pages over the range [addr, addr + len) to their backing storage locations. msync() optionally invalidates any copies so that further references to the pages will be obtained by the system from their backing storage locations. The backing storage for a modified MAP_SHARED mapping is the file the page is mapped to; the backing storage for a modified MAP_PRIVATE mapping is its swap area.

flags is a bit pattern built from the following values: 


    MS_ASYNC    perform asynchronous writes
    MS_SYNC    perform synchronous writes
    MS_INVALIDATE    invalidate mappings

If MS_ASYNC is set, msync() returns immediately once all write operations are scheduled; if MS_SYNC is set, msync() does not return until all write operations are completed.

MS_INVALIDATE invalidates all cached copies of data in memory, so that further references to the pages will be obtained by the system from their backing storage locations.

Return Values

Upon successful completion, the function msync() returns 0; otherwise, it returns -1 and sets errno to indicate the error.

Errors

EBUSY
Some or all of the addresses in the range [addr, addr + len) are locked and MC_SYNC with the MS_INVALIDATE option is specified.
EINVAL
addr is not a multiple of the page size as returned by sysconf(3C) .
flags
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.

See Also

mmap(2) , memcntl(2) , sysconf(3C)

Notes

msync() should be used by programs that require a memory object to be in a known state, such as in building transaction facilities.

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