[dpdk-dev] [PATCH v2] mbuf: outer offsets are undefined for non-tunnel packets

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

The default policy for offload-specific fields is that
they are undefined unless the corresponding offloads are
requested in mbuf ol_flags. This is also the case for outer
L2 and L3 length fields which must not be assumed to contain
zeros for non-tunnel packets. The patch clarifies this behaviour
in the comments. PMDs which mistakenly assume these fields
to be zero for non-tunnel packets are expected to comply
with the clarified comment and have dedicated fixes.

Signed-off-by: Ivan Malov <ivan.malov@oktetlabs.ru>
---
 lib/librte_mbuf/rte_mbuf.h | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index 0d9fef0..26a0b14 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -702,7 +702,18 @@ 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 are undefined for packets which don't request
+			 * any tunnel offloads (outer IP or UDP checksum,
+			 * tunnel TSO).
+			 *
+			 * PMDs are advised not to use these fields
+			 * unconditionally when calculating offsets.
+			 *
+			 * Applications are expected to set appropriate tunnel
+			 * offload flags when they fill in these fields.
+			 */
 			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;
-- 
1.8.3.1