[PATCH 1/2] nfsd/blocklayout: pretend we can send deviceid notifications

[Christoph Hellwig <hch@lst.de>]

Commit df52699e4fcef ("NFSv4.1: Don't cache deviceids that have no
notifications") causes the Linux NFS client stop caching deviceid
unless a server pretends to support deviceid notifications.  While
this behavior is stupid and the language around this area in rfc5661
is a mess carified by an errata that I submittted, Trond insists
on this behavior.  Not caching deviceids degrades block layout
performance massively as a GETDEVICEINFO is fairly expensive.

So add this hack to make the Linux client happy again.

Cc: stable@vger.kernel.org
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/nfsd/blocklayout.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/nfsd/blocklayout.c b/fs/nfsd/blocklayout.c
index 03d647b..58298fa6 100644
--- a/fs/nfsd/blocklayout.c
+++ b/fs/nfsd/blocklayout.c
@@ -181,6 +181,16 @@ nfsd4_block_proc_layoutcommit(struct inode *inode,
 }
 
 const struct nfsd4_layout_ops bl_layout_ops = {
+	/*
+	 * Pretend that we send notification to the client.  This is a blatant
+	 * lie to force recent Linux clients to cache our device IDs.
+	 * We rarely ever change the device ID, so the harm of leaking deviceids
+	 * for a while isn't too bad.  Unfortunately RFC5661 is a complete mess
+	 * in this regard, but I filed errata 4119 for this a while ago, and
+	 * hopefully the Linux client will eventually start caching deviceids
+	 * without this again.
+	 */
+	.notify_types		= NOTIFY_DEVICEID4_DELETE,
 	.proc_getdeviceinfo	= nfsd4_block_proc_getdeviceinfo,
 	.encode_getdeviceinfo	= nfsd4_block_encode_getdeviceinfo,
 	.proc_layoutget		= nfsd4_block_proc_layoutget,
-- 
1.9.1