NFS: make direct write path generate write requests concurrently

Duplicate infrastructure from direct read path that will allow write
path to generate multiple write requests concurrently.  This will
enable us to add support for aio in this path.

Temporarily we will lose the ability to do UNSTABLE writes followed by
a COMMIT in the direct write path.  However, all applications I am
aware of that use NFS O_DIRECT currently write in relatively small
chunks, so this should not be inconvenient in any way.

Test plan:
Millions of fsx-odirect ops. OraSim.

Signed-off-by: Chuck Lever <cel@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index f55827be4f8e..6c130a6b0f4d 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -407,6 +407,8 @@ extern int  nfs_writepage(struct page *page, struct writeback_control *wbc);
 extern int  nfs_writepages(struct address_space *, struct writeback_control *);
 extern int  nfs_flush_incompatible(struct file *file, struct page *page);
 extern int  nfs_updatepage(struct file *, struct page *, unsigned int, unsigned int);
+extern int nfs_writeback_done(struct rpc_task *, struct nfs_write_data *);
+extern void nfs_writedata_release(void *);
 
 /*
  * Try to write back everything synchronously (but check the