According to the ethdev doc, in general, PMD tx_burst() should not modify mbuf contents. To be more specific: ethdev/rte_ethdev.h:6396 ... * @note This function must not modify mbufs (including packets data) * unless the refcnt is 1. * An exception is the bonding PMD, which does not have "Tx prepare" support, * in this case, mbufs may be modified. ... Though why looking at eth_af_packet_tx(), it looks to me like it does modify the packet contents without any checks for refcnt, etc.: 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.
As Stephen Hemminger <stephen@networkplumber.org> pointed out: 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; So closing as not a bug.