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Subject: [PATCH] 9p/trans_virtio: discard zero-length reply
From:   Greg Kurz <groug@kaod.org>
To:     v9fs-developer@lists.sourceforge.net
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        "David S. Miller" <davem@davemloft.net>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Eric Van Hensbergen <ericvh@gmail.com>,
        Latchesar Ionkov <lucho@ionkov.net>,
        Ron Minnich <rminnich@sandia.gov>
Date:   Mon, 22 Jan 2018 22:02:05 +0100
Message-ID: <151665492548.14372.18325892476788349632.stgit@bahia.lan>
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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>
---
 net/9p/trans_virtio.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 0845aad4ba51..ca08c72ef4de 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -171,7 +171,8 @@ static void req_done(struct virtqueue *vq)
 		spin_unlock_irqrestore(&chan->lock, flags);
 		/* Wakeup if anyone waiting for VirtIO ring space. */
 		wake_up(chan->vc_wq);
-		p9_client_cb(chan->client, req, REQ_STATUS_RCVD);
+		if (len)
+			p9_client_cb(chan->client, req, REQ_STATUS_RCVD);
 	}
 }