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Subject: RE: [DPDK/ethdev Bug 1416] net/af_packet: tx_burst() can modify
 packets
Date: Tue, 16 Apr 2024 20:11:05 +0200
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Thread-Topic: [DPDK/ethdev Bug 1416] net/af_packet: tx_burst() can modify
 packets
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References: <bug-1416-3@http.bugs.dpdk.org/>
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From: =?iso-8859-1?Q?Morten_Br=F8rup?= <mb@smartsharesystems.com>
To: "Konstantin Ananyev" <konstantin.ananyev@huawei.com>,
 "Stephen Hemminger" <stephen@networkplumber.org>
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> > > > > static uint16_t
> > > > > eth_af_packet_tx(void *queue, struct rte_mbuf **bufs, uint16_t
> > > nb_pkts)
> > > > > {
> > > > >         ...
> > > > >         for (i =3D 0; i < nb_pkts; i++) {
> > > > >                 mbuf =3D *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;
> > >
> > > You are right, I missed that.
> > > Will close it then.
> >
> > Don't close, silent drop is also a bug.
> >
> > The VLAN tag could be insert when copying, as originally suggested.
>=20
> Agree, but to me that would be enhancement request, not a bug report.

Hmm... there is still a bug, although slightly different:

net/af_packet: tx_burst() silently drops packets with RTE_MBUF_F_TX_VLAN =
if mbuf is shared

And the suggested fixes would fix this (other) bug.

>=20
> >
> > Alternatively, set tpacket2_hdr's tp_vlan_tci and tp_vlan_tpid =
fields
> and set TP_STATUS_VLAN_VALID and
> > TP_STATUS_VLAN_TPID_VALID flags in tp_status. If the kernel reads
> those?