[ovs-dev] [PATCH] ofp: ensure that l2 is set in ofpmp_reserve()

Ben Pfaff blp at nicira.com
Tue Feb 12 17:15:24 UTC 2013

On Tue, Feb 12, 2013 at 05:19:38PM +0900, Simon Horman wrote:
> Ensure that the buffer returned by ofpmp_reserve() has buf->l2 set
> as this may be required by nxm_reg_load_to_nxast() when generating
> the reply to an stats request
> This problem was observed when dumping a large number of flows
> with set_field actions using ovs-ofctl dump-flows.
> Signed-off-by: Simon Horman <horms at verge.net.au>

Good catch.

I don't think ofpbuf_clone_with_headroom() is a good choice, because
headroom comes before the cloned data, whereas we want space to expand
after the cloned data.

I think that the following patch also fixes the problem.  Does it look
good to you?

diff --git a/lib/ofp-msgs.c b/lib/ofp-msgs.c
index efc4198..af4178e 100644
--- a/lib/ofp-msgs.c
+++ b/lib/ofp-msgs.c
@@ -851,6 +851,8 @@ ofpmp_reserve(struct list *replies, size_t len)
         next = ofpbuf_new(MAX(1024, hdrs_len + len));
         ofpbuf_put(next, msg->data, hdrs_len);
+        next->l2 = next->data;
+        next->l3 = ofpbuf_tail(next);
         list_push_back(replies, &next->list_node);
         *ofpmp_flags__(msg->data) |= htons(OFPSF_REPLY_MORE);



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