app/testpmd: fix eth packet dump for small buffers

[ upstream commit 3e6b0d5 ]

In the rather unlikely case where the first segment is too small to
contain an ethernet header, we can't go and directly dereference the
mbuf data buffer.

Using rte_pktmbuf_read is a little more expensive but this is still
acceptable for a debugging feature.

Fixes: af75078 ("first public release")

Signed-off-by: David Marchand <david.marchand@redhat.com>
Acked-by: Bernard Iremonger <bernard.iremonger@intel.com>

app/test-pmd/util.c

@@ -14,7 +14,7 @@
 #include "testpmd.h"
 
 static inline void
-print_ether_addr(const char *what, struct ether_addr *eth_addr)
+print_ether_addr(const char *what, const struct ether_addr *eth_addr)
 {
 	char buf[ETHER_ADDR_FMT_SIZE];
 	ether_format_addr(buf, ETHER_ADDR_FMT_SIZE, eth_addr);
@@ -26,7 +26,8 @@ dump_pkt_burst(uint16_t port_id, uint16_t queue, struct rte_mbuf *pkts[],
 	      uint16_t nb_pkts, int is_rx)
 {
 	struct rte_mbuf  *mb;
-	struct ether_hdr *eth_hdr;
+	const struct ether_hdr *eth_hdr;
+	struct ether_hdr _eth_hdr;
 	uint16_t eth_type;
 	uint64_t ol_flags;
 	uint16_t i, packet_type;
@@ -45,7 +46,7 @@ dump_pkt_burst(uint16_t port_id, uint16_t queue, struct rte_mbuf *pkts[],
 	       (unsigned int) nb_pkts);
 	for (i = 0; i < nb_pkts; i++) {
 		mb = pkts[i];
-		eth_hdr = rte_pktmbuf_mtod(mb, struct ether_hdr *);
+		eth_hdr = rte_pktmbuf_read(mb, 0, sizeof(_eth_hdr), &_eth_hdr);
 		eth_type = RTE_BE_TO_CPU_16(eth_hdr->ether_type);
 		ol_flags = mb->ol_flags;
 		packet_type = mb->packet_type;