msync(2)
synchronize a mapped region
LIBRARY
Lb libc
SYNOPSIS
In sys/mman.h
Ft int
Fn msync void *addr size_t len int flags
DESCRIPTION
The
Fn msync
system call
writes any modified pages back to the file system and updates
the file modification time.
If
Fa len
is 0, all modified pages within the region containing
Fa addr
will be flushed;
if
Fa len
is non-zero, only those pages containing
Fa addr
and
Fa len-1
succeeding locations will be examined.
The
Fa flags
argument may be specified as follows:
- MS_ASYNC
-
Return immediately
- MS_SYNC
-
Perform synchronous writes
- MS_INVALIDATE
-
Invalidate all cached data
RETURN VALUES
Rv -std msync
ERRORS
The
Fn msync
system call
will fail if:
- Bq Er EBUSY
-
Some or all of the pages in the specified region are locked and
MS_INVALIDATE
is specified.
- Bq Er EINVAL
-
The
Fa addr
argument
is not a multiple of the hardware page size.
- Bq Er ENOMEM
-
The addresses in the range starting at
Fa addr
and continuing for
Fa len
bytes are outside the range allowed for the address space of a
process or specify one or more pages that are not mapped.
- Bq Er EINVAL
-
The
Fa flags
argument
was both MS_ASYNC and MS_INVALIDATE.
Only one of these flags is allowed.
- Bq Er EIO
-
An error occurred while writing at least one of the pages in
the specified region.
HISTORY
The
Fn msync
system call first appeared in
BSD 4.4
BUGS
The
Fn 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.
