[dpdk-dev] [RFC PATCH] mbuf: move headers not fragmented check to checksum

[Andrew Rybchenko <arybchenko@solarflare.com>]

rte_validate_tx_offload() is used in Tx prepare callbacks
(RTE_LIBRTE_ETHDEV_DEBUG only) to check Tx offloads consistency.
Requirement that packet headers should not be fragmented is not
documented and unclear where it comes from except
rte_net_intel_cksum_prepare() functions which relies on it.

It could be NIC vendor specific driver or hardware limitation, but,
if so, it should be documented and checked in corresponding Tx
prepare callbacks.

Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
---
May be the check should be done in rte_net_intel_cksum_prepare()
under RTE_LIBRTE_ETHDEV_DEBUG only. Mainly I'd like to get feedback
on where the limitation comes from and idea to remove it from
rte_validate_tx_offload().

 lib/librte_mbuf/rte_mbuf.h | 12 ------------
 lib/librte_net/rte_net.h   | 17 +++++++++++++++++
 2 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index a7f67023a..14a3b472b 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -2257,23 +2257,11 @@ static inline int
 rte_validate_tx_offload(const struct rte_mbuf *m)
 {
 	uint64_t ol_flags = m->ol_flags;
-	uint64_t inner_l3_offset = m->l2_len;
 
 	/* Does packet set any of available offloads? */
 	if (!(ol_flags & PKT_TX_OFFLOAD_MASK))
 		return 0;
 
-	if (ol_flags & PKT_TX_OUTER_IP_CKSUM)
-		/* NB: elaborating the addition like this instead of using
-		 *     += gives the result uint64_t type instead of int,
-		 *     avoiding compiler warnings on gcc 8.1 at least */
-		inner_l3_offset = inner_l3_offset + m->outer_l2_len +
-				  m->outer_l3_len;
-
-	/* Headers are fragmented */
-	if (rte_pktmbuf_data_len(m) < inner_l3_offset + m->l3_len + m->l4_len)
-		return -ENOTSUP;
-
 	/* IP checksum can be counted only for IPv4 packet */
 	if ((ol_flags & PKT_TX_IP_CKSUM) && (ol_flags & PKT_TX_IPV6))
 		return -EINVAL;
diff --git a/lib/librte_net/rte_net.h b/lib/librte_net/rte_net.h
index e59760a0a..bd75aea8e 100644
--- a/lib/librte_net/rte_net.h
+++ b/lib/librte_net/rte_net.h
@@ -118,10 +118,27 @@ rte_net_intel_cksum_flags_prepare(struct rte_mbuf *m, uint64_t ol_flags)
 	struct udp_hdr *udp_hdr;
 	uint64_t inner_l3_offset = m->l2_len;
 
+	/*
+	 * Does packet set any of available offloads?
+	 * Mainly it is required to avoid fragmented headers check if
+	 * no offloads are requested.
+	 */
+	if (!(ol_flags & PKT_TX_OFFLOAD_MASK))
+		return 0;
+
 	if ((ol_flags & PKT_TX_OUTER_IP_CKSUM) ||
 		(ol_flags & PKT_TX_OUTER_IPV6))
 		inner_l3_offset += m->outer_l2_len + m->outer_l3_len;
 
+	/*
+	 * Check if headers are fragmented.
+	 * The check could be less strict depending on which offloads are
+	 * requested and headers to be used, but let's keep it simple.
+	 */
+	if (unlikely(rte_pktmbuf_data_len(m) <
+		     inner_l3_offset + m->l3_len + m->l4_len))
+		return -ENOTSUP;
+
 	if (ol_flags & PKT_TX_IPV4) {
 		ipv4_hdr = rte_pktmbuf_mtod_offset(m, struct ipv4_hdr *,
 				inner_l3_offset);
-- 
2.17.1