NFS: Optimise NFS close()

Close-to-open cache consistency rules really only require us to flush out
writes on calls to close(), and require us to revalidate attributes on the
very last close of the file.

Currently we appear to be doing a lot of extra attribute revalidation
and cache flushes.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index a55e69a..2041f68 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -152,6 +152,9 @@
 extern struct rpc_procinfo nfs4_procedures[];
 #endif
 
+/* proc.c */
+void nfs_close_context(struct nfs_open_context *ctx, int is_sync);
+
 /* dir.c */
 extern int nfs_access_cache_shrinker(int nr_to_scan, gfp_t gfp_mask);