[PATCH v10 07/19] net/pcap: allocate Tx bounce buffer

Stephen Hemminger
2026-01-30T01:14:41Z

To handle possible multi segment mbufs, the driver would allocate
a worst case 64k buffer on the stack. Since each Tx queue is
single threaded, better to allocate the buffer from hugepage
with rte_malloc when queue is setup.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
drivers/net/pcap/pcap_ethdev.c | 41 +++++++++++++++++++++-------------
1 file changed, 26 insertions(+), 15 deletions(-)

diff --git a/drivers/net/pcap/pcap_ethdev.c b/drivers/net/pcap/pcap_ethdev.c
index 61ba50e356..1a186142d3 100644
--- a/drivers/net/pcap/pcap_ethdev.c
+++ b/drivers/net/pcap/pcap_ethdev.c
@@ -12,6 +12,7 @@
#include <errno.h>
#include <sys/time.h>
#include <sys/types.h>
+#include <unistd.h>
#include <pcap.h>

#include <rte_cycles.h>
@@ -91,6 +92,9 @@ struct pcap_tx_queue {
struct queue_stat tx_stat;
char name[PATH_MAX];
char type[ETH_PCAP_ARG_MAXLEN];
+
+ /* Temp buffer used to for non-linear packets */
+ uint8_t *bounce_buf;
};

struct pmd_internals {
@@ -392,11 +396,12 @@ eth_pcap_tx_dumper(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
uint32_t tx_bytes = 0;
struct pcap_pkthdr header;
pcap_dumper_t *dumper;
- unsigned char temp_data[RTE_ETH_PCAP_SNAPLEN];
+ unsigned char *temp_data;
size_t len, caplen;

pp = rte_eth_devices[dumper_q->port_id].process_private;
dumper = pp->tx_dumper[dumper_q->queue_id];
+ temp_data = dumper_q->bounce_buf;

if (dumper == NULL || nb_pkts == 0)
return 0;
@@ -406,10 +411,6 @@ eth_pcap_tx_dumper(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
for (i = 0; i < nb_pkts; i++) {
mbuf = bufs[i];
len = caplen = rte_pktmbuf_pkt_len(mbuf);
- if (unlikely(!rte_pktmbuf_is_contiguous(mbuf) &&
- len > sizeof(temp_data))) {
- caplen = sizeof(temp_data);
- }

calculate_timestamp(&header.ts);
header.len = len;
@@ -419,7 +420,7 @@ eth_pcap_tx_dumper(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
* a pointer to temp_data after copying into it.
*/
pcap_dump((u_char *)dumper, &header,
- rte_pktmbuf_read(mbuf, 0, caplen, temp_data));
+ rte_pktmbuf_read(mbuf, 0, caplen, temp_data));

num_tx++;
tx_bytes += caplen;
@@ -474,11 +475,12 @@ eth_pcap_tx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
uint16_t num_tx = 0;
uint32_t tx_bytes = 0;
pcap_t *pcap;
- unsigned char temp_data[RTE_ETH_PCAP_SNAPLEN];
+ unsigned char *temp_data;
size_t len;

pp = rte_eth_devices[tx_queue->port_id].process_private;
pcap = pp->tx_pcap[tx_queue->queue_id];
+ temp_data = tx_queue->bounce_buf;

if (unlikely(nb_pkts == 0 || pcap == NULL))
return 0;
@@ -486,13 +488,6 @@ eth_pcap_tx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
for (i = 0; i < nb_pkts; i++) {
mbuf = bufs[i];
len = rte_pktmbuf_pkt_len(mbuf);
- if (unlikely(!rte_pktmbuf_is_contiguous(mbuf) &&
- len > sizeof(temp_data))) {
- PMD_LOG(ERR,
- "Dropping multi segment PCAP packet. Size (%zd) > max size (%zd).",
- len, sizeof(temp_data));
- continue;
- }

/* rte_pktmbuf_read() returns a pointer to the data directly
* in the mbuf (when the mbuf is contiguous) or, otherwise,
@@ -962,7 +957,7 @@ static int
eth_tx_queue_setup(struct rte_eth_dev *dev,
uint16_t tx_queue_id,
uint16_t nb_tx_desc __rte_unused,
- unsigned int socket_id __rte_unused,
+ unsigned int socket_id,
const struct rte_eth_txconf *tx_conf __rte_unused)
{
struct pmd_internals *internals = dev->data->dev_private;
@@ -970,11 +965,26 @@ eth_tx_queue_setup(struct rte_eth_dev *dev,

pcap_q->port_id = dev->data->port_id;
pcap_q->queue_id = tx_queue_id;
+ pcap_q->bounce_buf = rte_malloc_socket(NULL, RTE_ETH_PCAP_SNAPSHOT_LEN,
+ RTE_CACHE_LINE_SIZE, socket_id);
+ if (pcap_q->bounce_buf == NULL)
+ return -ENOMEM;
+
dev->data->tx_queues[tx_queue_id] = pcap_q;

return 0;
}

+static void
+eth_tx_queue_release(struct rte_eth_dev *dev, uint16_t tx_queue_id)
+{
+ struct pmd_internals *internals = dev->data->dev_private;
+ struct pcap_tx_queue *pcap_q = &internals->tx_queue[tx_queue_id];
+
+ rte_free(pcap_q->bounce_buf);
+ pcap_q->bounce_buf = NULL;
+}
+
static int
eth_rx_queue_start(struct rte_eth_dev *dev, uint16_t rx_queue_id)
{
@@ -1015,6 +1025,7 @@ static const struct eth_dev_ops ops = {
.dev_infos_get = eth_dev_info,
.rx_queue_setup = eth_rx_queue_setup,
.tx_queue_setup = eth_tx_queue_setup,
+ .tx_queue_release = eth_tx_queue_release,
.rx_queue_start = eth_rx_queue_start,
.tx_queue_start = eth_tx_queue_start,
.rx_queue_stop = eth_rx_queue_stop,
--
2.51.0