MSYNC(2) |
FreeBSD System Calls Manual |
MSYNC(2) |
NAME
msync —
synchronize a mapped region
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include < sys/mman.h>
int
msync( void *addr, size_t len, int flags);
DESCRIPTION
The
msync() system call writes any modified pages back to the file system and updates the file modification time. If
len is 0, all modified pages within the region containing
addr will be flushed; if
len is non-zero, only those pages containing
addr and
len-1 succeeding locations will be examined. The
flags argument may be specified as follows:
-
MS_ASYNC
-
Return immediately
-
MS_SYNC
-
Perform synchronous writes
-
MS_INVALIDATE
-
Invalidate all cached data
RETURN VALUES
The
msync() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable
errno is set to indicate the error.
ERRORS
The
msync() system call will fail if:
-
[
EBUSY]
-
Some or all of the pages in the specified region are locked and
MS_INVALIDATE is specified.
-
[
EINVAL]
-
The
addr argument is not a multiple of the hardware page size.
-
[
ENOMEM]
-
The addresses in the range starting at
addr and continuing for
len bytes are outside the range allowed for the address space of a process or specify one or more pages that are not mapped.
-
[
EINVAL]
-
The
flags argument was both MS_ASYNC and MS_INVALIDATE. Only one of these flags is allowed.
-
[
EIO]
-
An error occurred while writing at least one of the pages in the specified region.
HISTORY
The
msync() system call first appeared in
4.4BSD.
BUGS
The
msync() system call is usually not needed since
BSD implements a coherent file system buffer cache. However, it may be used to associate dirty VM pages with file system buffers and thus cause them to be flushed to physical media sooner rather than later.