[PATCH v16 11/21] net/pcap: support VLAN strip and insert offloads

Stephen Hemminger
2026-02-16T18:15:27Z

Add VLAN tag handling to the pcap PMD, consistent with how virtio
and af_packet drivers implement it.

RX strip: when RTE_ETH_RX_OFFLOAD_VLAN_STRIP is enabled, the driver
calls rte_vlan_strip() on received packets in both normal and
infinite_rx modes. For infinite_rx, offloads are deferred to
packet delivery rather than applied during ring fill, so the
stored template packets remain unmodified.

TX insert: when RTE_MBUF_F_TX_VLAN is set on an mbuf, the driver
inserts the VLAN tag via rte_vlan_insert() before writing to pcap
or sending to the interface. Indirect or shared mbufs get a new
header mbuf to avoid modifying the original.

Runtime reconfiguration is supported through vlan_offload_set,
which propagates the strip setting to all active RX queues.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
doc/guides/nics/features/pcap.ini | 1 +
doc/guides/nics/pcap.rst | 11 +++
doc/guides/rel_notes/release_26_03.rst | 5 ++
drivers/net/pcap/pcap_ethdev.c | 118 ++++++++++++++++++++++++-
4 files changed, 131 insertions(+), 4 deletions(-)

diff --git a/doc/guides/nics/features/pcap.ini b/doc/guides/nics/features/pcap.ini
index b0dac3cca7..814bc2119f 100644
--- a/doc/guides/nics/features/pcap.ini
+++ b/doc/guides/nics/features/pcap.ini
@@ -10,6 +10,7 @@ Scattered Rx = Y
Timestamp offload = Y
Basic stats = Y
Stats per queue = Y
+VLAN offload = Y
Multiprocess aware = Y
FreeBSD = Y
Linux = Y
diff --git a/doc/guides/nics/pcap.rst b/doc/guides/nics/pcap.rst
index fbfe854bb1..bed5006a42 100644
--- a/doc/guides/nics/pcap.rst
+++ b/doc/guides/nics/pcap.rst
@@ -247,3 +247,14 @@ will be discarded by the Rx flushing operation.
The network interface provided to the PMD should be up.
The PMD will return an error if the interface is down,
and the PMD itself won't change the status of the external network interface.
+
+Features and Limitations
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+* The PMD will re-insert the VLAN tag transparently to the packet if the kernel
+ strips it, as long as the ``RTE_ETH_RX_OFFLOAD_VLAN_STRIP`` is not enabled by the
+ application.
+
+* The PMD will transparently insert a VLAN tag to transmitted packets if
+ ``RTE_ETH_TX_OFFLOAD_VLAN_INSERT`` is enabled and the mbuf has ``RTE_MBUF_F_TX_VLAN``
+ set.
diff --git a/doc/guides/rel_notes/release_26_03.rst b/doc/guides/rel_notes/release_26_03.rst
index cb9fda07a8..2d0208ddac 100644
--- a/doc/guides/rel_notes/release_26_03.rst
+++ b/doc/guides/rel_notes/release_26_03.rst
@@ -92,6 +92,11 @@ New Features
Added handling of the key combination Control+L
to clear the screen before redisplaying the prompt.

+* **Updated PCAP ethernet driver.**
+
+ * Added support for VLAN insertion and stripping.
+
+
Removed Items
-------------

diff --git a/drivers/net/pcap/pcap_ethdev.c b/drivers/net/pcap/pcap_ethdev.c
index 2742e0ca80..e794d2ab8d 100644
--- a/drivers/net/pcap/pcap_ethdev.c
+++ b/drivers/net/pcap/pcap_ethdev.c
@@ -76,6 +76,7 @@ struct queue_missed_stat {
struct pcap_rx_queue {
uint16_t port_id;
uint16_t queue_id;
+ bool vlan_strip;
struct rte_mempool *mb_pool;
struct queue_stat rx_stat;
struct queue_missed_stat missed_stat;
@@ -106,6 +107,7 @@ struct pmd_internals {
bool single_iface;
bool phy_mac;
bool infinite_rx;
+ bool vlan_strip;
};

struct pmd_process_private {
@@ -270,7 +272,11 @@ eth_pcap_rx_infinite(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
bufs[i]->data_len = pcap_buf->data_len;
bufs[i]->pkt_len = pcap_buf->pkt_len;
bufs[i]->port = pcap_q->port_id;
- rx_bytes += pcap_buf->data_len;
+
+ if (pcap_q->vlan_strip)
+ rte_vlan_strip(bufs[i]);
+
+ rx_bytes += bufs[i]->data_len;

/* Enqueue packet back on ring to allow infinite rx. */
rte_ring_enqueue(pcap_q->pkts, pcap_buf);
@@ -336,6 +342,10 @@ eth_pcap_rx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
}

mbuf->pkt_len = len;
+
+ if (pcap_q->vlan_strip)
+ rte_vlan_strip(mbuf);
+
uint64_t us = (uint64_t)header->ts.tv_sec * US_PER_S + header->ts.tv_usec;

*RTE_MBUF_DYNFIELD(mbuf, timestamp_dynfield_offset, rte_mbuf_timestamp_t *) = us;
@@ -382,6 +392,57 @@ calculate_timestamp(struct timeval *ts) {
}
}

+
+/*
+ * If Vlan offload flag is present, insert the vlan.
+ */
+static inline int
+eth_pcap_tx_vlan(struct pcap_tx_queue *tx_queue, struct rte_mbuf **mbuf)
+{
+ struct rte_mbuf *mb = *mbuf;
+
+ if ((mb->ol_flags & RTE_MBUF_F_TX_VLAN) == 0)
+ return 0;
+
+ if (unlikely(mb->data_len < RTE_ETHER_HDR_LEN)) {
+ PMD_TX_LOG(ERR, "mbuf missing ether header");
+ goto error;
+ }
+
+ /* If indirect or shared then need another buffer to hold VLAN header? */
+ if (!RTE_MBUF_DIRECT(mb) || rte_mbuf_refcnt_read(mb) > 1) {
+ struct rte_mbuf *mh = rte_pktmbuf_alloc(mb->pool);
+ if (unlikely(mh == NULL)) {
+ PMD_TX_LOG(ERR, "mbuf pool exhausted on transmit vlan");
+ goto error;
+ }
+
+ /* Move original ethernet header into new mbuf */
+ memcpy(rte_pktmbuf_mtod(mh, void *),
+ rte_pktmbuf_mtod(mb, void *), RTE_ETHER_HDR_LEN);
+
+ rte_pktmbuf_adj(mb, RTE_ETHER_HDR_LEN);
+ mh->nb_segs = mb->nb_segs + 1;
+ mh->data_len = RTE_ETHER_HDR_LEN;
+ mh->pkt_len = mb->pkt_len + RTE_ETHER_HDR_LEN;
+ mh->ol_flags = mb->ol_flags;
+ mh->next = mb;
+
+ *mbuf = mh;
+ }
+
+ int ret = rte_vlan_insert(mbuf);
+ if (unlikely(ret != 0)) {
+ PMD_TX_LOG(ERR, "Vlan insert failed: %s", strerror(-ret));
+ goto error;
+ }
+ return 0;
+error:
+ rte_pktmbuf_free(*mbuf);
+ tx_queue->tx_stat.err_pkts++;
+ return -1;
+}
+
/*
* Callback to handle writing packets to a pcap file.
*/
@@ -407,13 +468,17 @@ eth_pcap_tx_dumper(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
/* writes the nb_pkts packets to the previously opened pcap file
* dumper */
for (i = 0; i < nb_pkts; i++) {
- struct rte_mbuf *mbuf = bufs[i];
uint32_t len, caplen;
const uint8_t *data;

+ if (eth_pcap_tx_vlan(dumper_q, &bufs[i]) < 0)
+ continue;
+
+ struct rte_mbuf *mbuf = bufs[i];
len = caplen = rte_pktmbuf_pkt_len(mbuf);

calculate_timestamp(&header.ts);
+
header.len = len;
header.caplen = caplen;

@@ -498,6 +563,9 @@ eth_pcap_tx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
return 0;

for (i = 0; i < nb_pkts; i++) {
+ if (eth_pcap_tx_vlan(tx_queue, &bufs[i]) < 0)
+ continue;
+
struct rte_mbuf *mbuf = bufs[i];
uint32_t len = rte_pktmbuf_pkt_len(mbuf);
const uint8_t *data;
@@ -753,8 +821,13 @@ eth_dev_stop(struct rte_eth_dev *dev)
}

static int
-eth_dev_configure(struct rte_eth_dev *dev __rte_unused)
+eth_dev_configure(struct rte_eth_dev *dev)
{
+ struct pmd_internals *internals = dev->data->dev_private;
+ struct rte_eth_conf *dev_conf = &dev->data->dev_conf;
+ const struct rte_eth_rxmode *rxmode = &dev_conf->rxmode;
+
+ internals->vlan_strip = !!(rxmode->offloads & RTE_ETH_RX_OFFLOAD_VLAN_STRIP);
return 0;
}

@@ -770,7 +843,9 @@ eth_dev_info(struct rte_eth_dev *dev,
dev_info->max_rx_queues = dev->data->nb_rx_queues;
dev_info->max_tx_queues = dev->data->nb_tx_queues;
dev_info->min_rx_bufsize = 0;
- dev_info->tx_offload_capa = RTE_ETH_TX_OFFLOAD_MULTI_SEGS;
+ dev_info->tx_offload_capa = RTE_ETH_TX_OFFLOAD_MULTI_SEGS |
+ RTE_ETH_TX_OFFLOAD_VLAN_INSERT;
+ dev_info->rx_offload_capa = RTE_ETH_RX_OFFLOAD_VLAN_STRIP;

return 0;
}
@@ -917,6 +992,7 @@ eth_rx_queue_setup(struct rte_eth_dev *dev,
pcap_q->mb_pool = mb_pool;
pcap_q->port_id = dev->data->port_id;
pcap_q->queue_id = rx_queue_id;
+ pcap_q->vlan_strip = internals->vlan_strip;
dev->data->rx_queues[rx_queue_id] = pcap_q;

if (internals->infinite_rx) {
@@ -926,6 +1002,7 @@ eth_rx_queue_setup(struct rte_eth_dev *dev,
uint64_t pcap_pkt_count = 0;
struct rte_mbuf *bufs[1];
pcap_t **pcap;
+ bool save_vlan_strip;

pp = rte_eth_devices[pcap_q->port_id].process_private;
pcap = &pp->rx_pcap[pcap_q->queue_id];
@@ -945,11 +1022,20 @@ eth_rx_queue_setup(struct rte_eth_dev *dev,
if (!pcap_q->pkts)
return -ENOENT;

+ /*
+ * Temporarily disable offloads while filling the ring
+ * with raw packets. VLAN strip and timestamp will be
+ * applied later in eth_pcap_rx_infinite() on each copy.
+ */
+ save_vlan_strip = pcap_q->vlan_strip;
+ pcap_q->vlan_strip = false;
+
/* Fill ring with packets from PCAP file one by one. */
while (eth_pcap_rx(pcap_q, bufs, 1)) {
/* Check for multiseg mbufs. */
if (bufs[0]->nb_segs != 1) {
infinite_rx_ring_free(pcap_q->pkts);
+ pcap_q->vlan_strip = save_vlan_strip;
PMD_LOG(ERR,
"Multiseg mbufs are not supported in infinite_rx mode.");
return -EINVAL;
@@ -959,6 +1045,9 @@ eth_rx_queue_setup(struct rte_eth_dev *dev,
(void * const *)bufs, 1, NULL);
}

+ /* Restore offloads for use during packet delivery */
+ pcap_q->vlan_strip = save_vlan_strip;
+
if (rte_ring_count(pcap_q->pkts) < pcap_pkt_count) {
infinite_rx_ring_free(pcap_q->pkts);
PMD_LOG(ERR,
@@ -1043,6 +1132,26 @@ eth_tx_queue_stop(struct rte_eth_dev *dev, uint16_t tx_queue_id)
return 0;
}

+static int
+eth_vlan_offload_set(struct rte_eth_dev *dev, int mask)
+{
+ struct pmd_internals *internals = dev->data->dev_private;
+ unsigned int i;
+
+ if (mask & RTE_ETH_VLAN_STRIP_MASK) {
+ bool vlan_strip = !!(dev->data->dev_conf.rxmode.offloads &
+ RTE_ETH_RX_OFFLOAD_VLAN_STRIP);
+
+ internals->vlan_strip = vlan_strip;
+
+ /* Update all RX queues */
+ for (i = 0; i < dev->data->nb_rx_queues; i++)
+ internals->rx_queue[i].vlan_strip = vlan_strip;
+ }
+
+ return 0;
+}
+
static const struct eth_dev_ops ops = {
.dev_start = eth_dev_start,
.dev_stop = eth_dev_stop,
@@ -1059,6 +1168,7 @@ static const struct eth_dev_ops ops = {
.link_update = eth_link_update,
.stats_get = eth_stats_get,
.stats_reset = eth_stats_reset,
+ .vlan_offload_set = eth_vlan_offload_set,
};

static int
--
2.51.0