Re: [DPDK/ethdev Bug 1416] net/af_packet: tx_burst() can modify packets

[Stephen Hemminger <stephen@networkplumber.org>]

On Tue, 16 Apr 2024 10:29:53 +0000
bugzilla@dpdk.org wrote:

> static uint16_t
> eth_af_packet_tx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
> {
>         ...
>         for (i = 0; i < nb_pkts; i++) {
>                 mbuf = *bufs++;
> 
>                 ...
> 
>                 /* insert vlan info if necessary */
>                 if (mbuf->ol_flags & RTE_MBUF_F_TX_VLAN) {
>                         if (rte_vlan_insert(&mbuf)) {
>                                 rte_pktmbuf_free(mbuf);
>                                 continue; 
> 
> AFAIU, it does copy of mbuf contents into pbuf anyway (just few line below).
> So the fix might be - simply insert VLAN tag at copying stage.
> Feel free to correct me, if I missed something.

vlan_insert will fail if the mbuf is has refcnt > 1.

static inline int rte_vlan_insert(struct rte_mbuf **m)
{
	struct rte_ether_hdr *oh, *nh;
	struct rte_vlan_hdr *vh;

	/* Can't insert header if mbuf is shared */
	if (!RTE_MBUF_DIRECT(*m) || rte_mbuf_refcnt_read(*m) > 1)
		return -EINVAL;