[PATCH 3.2 080/153] 9p/trans_virtio: discard zero-length reply

[Ben Hutchings <ben@decadent.org.uk>]

3.2.102-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Greg Kurz <groug@kaod.org>

commit 26d99834f89e76514076d9cd06f61e56e6a509b8 upstream.

When a 9p request is successfully flushed, the server is expected to just
mark it as used without sending a 9p reply (ie, without writing data into
the buffer). In this case, virtqueue_get_buf() will return len == 0 and
we must not report a REQ_STATUS_RCVD status to the client, otherwise the
client will erroneously assume the request has not been flushed.

Signed-off-by: Greg Kurz <groug@kaod.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 net/9p/trans_virtio.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -163,7 +163,8 @@ static void req_done(struct virtqueue *v
 		P9_DPRINTK(P9_DEBUG_TRANS, ": lookup tag %d\n", rc->tag);
 		req = p9_tag_lookup(chan->client, rc->tag);
 		req->status = REQ_STATUS_RCVD;
-		p9_client_cb(chan->client, req);
+		if (len)
+			p9_client_cb(chan->client, req);
 	}
 }