net/pcap: fix Rx with small buffers

[ upstream commit 6653d81 ]

If the pkt pool contains only buffers smaller than the default headroom,
then the driver will compute an invalid buffer size (negative value cast
to an uint16_t).
Rely on the mbuf api to check how much space is available in the mbuf.

Fixes: 6eb0ae2 ("pcap: fix mbuf allocation")

Signed-off-by: David Marchand <david.marchand@redhat.com>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>

drivers/net/pcap/rte_eth_pcap.c

@@ -188,7 +188,6 @@ eth_pcap_rx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 	struct rte_mbuf *mbuf;
 	struct pcap_rx_queue *pcap_q = queue;
 	uint16_t num_rx = 0;
-	uint16_t buf_size;
 	uint32_t rx_bytes = 0;
 	pcap_t *pcap;
 
@@ -211,11 +210,7 @@ eth_pcap_rx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 		if (unlikely(mbuf == NULL))
 			break;
 
-		/* Now get the space available for data in the mbuf */
-		buf_size = rte_pktmbuf_data_room_size(pcap_q->mb_pool) -
-				RTE_PKTMBUF_HEADROOM;
-
-		if (header.caplen <= buf_size) {
+		if (header.caplen <= rte_pktmbuf_tailroom(mbuf)) {
 			/* pcap packet will fit in the mbuf, can copy it */
 			rte_memcpy(rte_pktmbuf_mtod(mbuf, void *), packet,
 					header.caplen);