tree 61607917bd96095c5f35784593298fd7581b8b6c
parent 7c5d187581f57657de79e795602d9f1a0254c88c
author Christoph Hellwig <hch@lst.de> 1410362610 -0700
committer Trond Myklebust <trond.myklebust@primarydata.com> 1410378422 -0700

pnfs: add flag to force read-modify-write in ->write_begin

Like all block based filesystems, the pNFS block layout driver can't read
or write at a byte granularity and thus has to perform read-modify-write
cycles on writes smaller than this granularity.

Add a flag so that the core NFS code always reads a whole page when
starting a smaller write, so that we can do it in the place where the VFS
expects it instead of doing in very deadlock prone way in the writeback
handler.

Note that in theory we could do less than page size reads here for disks
that have a smaller sector size which are served by a server with a smaller
pnfs block size.  But so far that doesn't seem like a worthwhile
optimization.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>