<html>
<head>
<base href="https://bugs.dpdk.org/">
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<body><table border="1" cellspacing="0" cellpadding="8" class="bz_new_table">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_UNCONFIRMED "
title="UNCONFIRMED - net/af_packet: tx_burst() can modify packets"
href="https://bugs.dpdk.org/show_bug.cgi?id=1416">1416</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>net/af_packet: tx_burst() can modify packets
</td>
</tr>
<tr>
<th>Product</th>
<td>DPDK
</td>
</tr>
<tr>
<th>Version</th>
<td>24.03
</td>
</tr>
<tr>
<th>Hardware</th>
<td>All
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>UNCONFIRMED
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>Normal
</td>
</tr>
<tr>
<th>Component</th>
<td>ethdev
</td>
</tr>
<tr>
<th>Assignee</th>
<td>dev@dpdk.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>konstantin.v.ananyev@yandex.ru
</td>
</tr>
<tr>
<th>Target Milestone</th>
<td>---
</td>
</tr></table>
<p>
<div class="bz_comment_block">
<pre class="bz_comment_text">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.
</pre>
</div>
</p>
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