[dpdk-dev] [RFC PATCH] mbuf: outer offsets must be zero for non-tunnel packets

[Ivan Malov <ivan.malov@oktetlabs.ru>]

Make sure that outer L2 and L3 header length fields are
equal to zero for non-tunnel packets in order to ensure
consistent and predictable behaviour in network drivers.
Explain this expectation in comments to help developers.

Signed-off-by: Ivan Malov <ivan.malov@oktetlabs.ru>
Reviewed-by: Andrew Rybchenko <arybchenko@solarflare.com>
---

Notes:
    At the time of writing a couple of network drivers rely on
    the statement (i40e, ice) whilst more drivers have runtime
    conditional checks to guard all references to these fields.
    This patch is likely to relieve datapath checks in drivers.

 lib/librte_mbuf/rte_mbuf.h | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index f7886dc..9d316ef 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -696,7 +696,12 @@ struct rte_mbuf {
 			uint64_t tso_segsz:RTE_MBUF_TSO_SEGSZ_BITS;
 			/**< TCP TSO segment size */
 
-			/* fields for TX offloading of tunnels */
+			/*
+			 * Fields for Tx offloading of tunnels.
+			 * These fields must be equal to zero in the case
+			 * when (ol_flags & PKT_TX_TUNNEL_MASK) == 0,
+			 * i.e. for all non-tunnel packets.
+			 */
 			uint64_t outer_l3_len:RTE_MBUF_OUTL3_LEN_BITS;
 			/**< Outer L3 (IP) Hdr Length. */
 			uint64_t outer_l2_len:RTE_MBUF_OUTL2_LEN_BITS;
@@ -2370,6 +2375,11 @@ static inline int rte_pktmbuf_chain(struct rte_mbuf *head, struct rte_mbuf *tail
 			!(ol_flags & PKT_TX_OUTER_IPV4))
 		return -EINVAL;
 
+	/* Outer L2/L3 offsets must be equal to zero for non-tunnel packets. */
+	if ((ol_flags & PKT_TX_TUNNEL_MASK) == 0 &&
+	    m->outer_l2_len + m->outer_l3_len != 0)
+		return -EINVAL;
+
 	return 0;
 }
 
-- 
1.8.3.1