[ovs-dev] [RFC PATCH V4 3/9] dp-packet: fix put_uninit for multi-seg mbufs

[Mark Kavanagh]

dp_packet_put_uninit(dp_packet, size) appends 'size' bytes to the tail
of a dp_packet. In the case of multi-segment mbufs, it is the data
length of the last mbuf in the mbuf chain that should be adjusted by
'size' bytes.

In its current implementation, dp_packet_put_uninit() adjusts the
dp_packet's size via a call to dp_packet_set_size(); however, this
adjusts the data length of the first mbuf in the chain, which is
incorrect in the case of multi-segment mbufs. Instead, traverse the
mbuf chain to locate the final mbuf of said chain, and update its
data_len[1]. To finish, increase the packet length of the entire
mbuf[2] by 'size'.

[1] In the case of a single-segment mbuf, this is the mbuf itself.
[2] This is stored in the first mbuf of an mbuf chain.

Signed-off-by: Mark Kavanagh <mark.b.kavanagh at intel.com>
---
 lib/dp-packet.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/lib/dp-packet.c b/lib/dp-packet.c
index 443c225..ad71486 100644
--- a/lib/dp-packet.c
+++ b/lib/dp-packet.c
@@ -322,7 +322,27 @@ dp_packet_put_uninit(struct dp_packet *b, size_t size)
     void *p;
     dp_packet_prealloc_tailroom(b, size);
     p = dp_packet_tail(b);
+#ifdef DPDK_NETDEV
+    if (b->source == DPBUF_DPDK) {
+        struct rte_mbuf *buf = &(b->mbuf);
+        /* In the case of multi-segment mbufs, the data length of the last mbuf
+         * should be adjusted by 'size' bytes. A call to dp_packet_size() would
+         * adjust the data length of the first mbuf in the segment, so we avoid
+         * invoking same; as a result, the packet length of the entire mbuf
+         * chain (stored in the first mbuf of said chain) must be adjusted here
+         * instead.
+         */
+        while (buf->next) {
+            buf = buf->next;
+        }
+        buf->data_len += size;
+        b->mbuf.pkt_len += size;
+    } else {
+#endif
     dp_packet_set_size(b, dp_packet_size(b) + size);
+#ifdef DPDK_NETDEV
+    }
+#endif
     return p;
 }
 
-- 
1.9.3