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.