[PATCH v20 22/25] net/pcap: add link status change support for iface mode

[Stephen Hemminger <stephen@networkplumber.org>]

Add LSC interrupt support for pass-through (iface=) mode so
applications can receive link state change notifications via
the standard ethdev callback mechanism.

Uses alarm-based polling to periodically check the underlying
interface state via osdep_iface_link_get(). The LSC flag is
advertised only for iface mode devices, and polling is gated
on the application enabling intr_conf.lsc in port configuration.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 doc/guides/nics/features/pcap.ini      |  1 +
 doc/guides/nics/pcap.rst               |  5 +++
 doc/guides/rel_notes/release_26_03.rst |  1 +
 drivers/net/pcap/pcap_ethdev.c         | 45 ++++++++++++++++++++++++++
 4 files changed, 52 insertions(+)

diff --git a/doc/guides/nics/features/pcap.ini b/doc/guides/nics/features/pcap.ini
index ec7c91c650..b409ecd597 100644
--- a/doc/guides/nics/features/pcap.ini
+++ b/doc/guides/nics/features/pcap.ini
@@ -5,6 +5,7 @@
 ;
 [Features]
 Link status          = Y
+Link status event    = Y
 Queue start/stop     = Y
 Timestamp offload    = Y
 Basic stats          = Y
diff --git a/doc/guides/nics/pcap.rst b/doc/guides/nics/pcap.rst
index 2754e205c7..72f2250790 100644
--- a/doc/guides/nics/pcap.rst
+++ b/doc/guides/nics/pcap.rst
@@ -278,3 +278,8 @@ Features and Limitations
 
 *  The PMD will insert the pcap header packet timestamp with nanoseconds resolution and
    UNIX origin, i.e. time since 1-JAN-1970 UTC, if ``RTE_ETH_RX_OFFLOAD_TIMESTAMP`` is enabled.
+
+*  In ``iface`` mode, the PMD supports link status change (LSC) notifications.
+   When the application enables ``intr_conf.lsc`` in the port configuration,
+   the driver polls the underlying network interface once per second and generates an
+   ``RTE_ETH_EVENT_INTR_LSC`` callback when the link state changes.
diff --git a/doc/guides/rel_notes/release_26_03.rst b/doc/guides/rel_notes/release_26_03.rst
index dc3a0fa81f..d1bc6ba493 100644
--- a/doc/guides/rel_notes/release_26_03.rst
+++ b/doc/guides/rel_notes/release_26_03.rst
@@ -124,6 +124,7 @@ New Features
   * Added support for reporting link state in ``iface`` mode.
   * Receive timestamps support nanosecond precision.
   * Added ``snaplen`` devarg to configure packet capture snapshot length.
+  * Added support for Link State interrupt in ``iface`` mode.
 
 
 Removed Items
diff --git a/drivers/net/pcap/pcap_ethdev.c b/drivers/net/pcap/pcap_ethdev.c
index d8a924b0cd..2d64032474 100644
--- a/drivers/net/pcap/pcap_ethdev.c
+++ b/drivers/net/pcap/pcap_ethdev.c
@@ -17,6 +17,7 @@
 
 #include <pcap.h>
 
+#include <rte_alarm.h>
 #include <rte_cycles.h>
 #include <rte_ring.h>
 #include <rte_ethdev.h>
@@ -48,6 +49,8 @@
 /* This is defined in libpcap but not exposed in headers */
 #define ETH_PCAP_MAXIMUM_SNAPLEN      262144
 
+#define ETH_PCAP_LSC_POLL_INTERVAL_US (1000 * 1000) /* 1 second */
+
 #define ETH_PCAP_ARG_MAXLEN	64
 
 #define RTE_PMD_PCAP_MAX_QUEUES 16
@@ -115,6 +118,7 @@ struct pmd_internals {
 	bool vlan_strip;
 	bool rx_scatter;
 	bool timestamp_offloading;
+	bool lsc_active;
 };
 
 struct pmd_process_private {
@@ -163,6 +167,9 @@ static const char *valid_arguments[] = {
 
 RTE_LOG_REGISTER_DEFAULT(eth_pcap_logtype, NOTICE);
 
+/* Forward declarations */
+static int eth_link_update(struct rte_eth_dev *dev, int wait_to_complete);
+
 static struct queue_missed_stat*
 queue_missed_stat_update(struct rte_eth_dev *dev, unsigned int qid)
 {
@@ -766,6 +773,28 @@ count_packets_in_pcap(pcap_t **pcap, struct pcap_rx_queue *pcap_q)
 	return pcap_pkt_count;
 }
 
+/*
+ * Periodic alarm to poll link state.
+ * Enabled when link state interrupt is enabled in single_iface mode.
+ */
+static void
+eth_pcap_lsc_alarm(void *arg)
+{
+	struct rte_eth_dev *dev = arg;
+	struct pmd_internals *internals = dev->data->dev_private;
+	struct rte_eth_link old_link, new_link;
+
+	rte_eth_linkstatus_get(dev, &old_link);
+	eth_link_update(dev, 0);
+	rte_eth_linkstatus_get(dev, &new_link);
+
+	if (old_link.link_status != new_link.link_status)
+		rte_eth_dev_callback_process(dev, RTE_ETH_EVENT_INTR_LSC, NULL);
+
+	if (internals->lsc_active)
+		rte_eal_alarm_set(ETH_PCAP_LSC_POLL_INTERVAL_US, eth_pcap_lsc_alarm, dev);
+}
+
 static int
 set_iface_direction(const char *iface, pcap_t *pcap,
 		pcap_direction_t direction)
@@ -848,6 +877,13 @@ eth_dev_start(struct rte_eth_dev *dev)
 
 	dev->data->dev_link.link_status = RTE_ETH_LINK_UP;
 
+	/* Start LSC polling for iface mode if application requested it */
+	if (internals->single_iface && dev->data->dev_conf.intr_conf.lsc) {
+		internals->lsc_active = true;
+		rte_eal_alarm_set(ETH_PCAP_LSC_POLL_INTERVAL_US,
+				  eth_pcap_lsc_alarm, dev);
+	}
+
 	return 0;
 }
 
@@ -865,6 +901,12 @@ eth_dev_stop(struct rte_eth_dev *dev)
 
 	/* Special iface case. Single pcap is open and shared between tx/rx. */
 	if (internals->single_iface) {
+		/* Cancel LSC polling before closing pcap handles */
+		if (internals->lsc_active) {
+			internals->lsc_active = false;
+			rte_eal_alarm_cancel(eth_pcap_lsc_alarm, dev);
+		}
+
 		queue_missed_stat_on_stop_update(dev, 0);
 		if (pp->tx_pcap[0] != NULL) {
 			pcap_close(pp->tx_pcap[0]);
@@ -1661,6 +1703,9 @@ eth_from_pcaps(struct rte_vdev_device *vdev,
 		internals->if_index =
 			osdep_iface_index_get(rx_queues->queue[0].name);
 
+		/* Enable LSC interrupt support for iface mode */
+		eth_dev->data->dev_flags |= RTE_ETH_DEV_INTR_LSC;
+
 		/* phy_mac arg is applied only if "iface" devarg is provided */
 		if (rx_queues->phy_mac) {
 			if (eth_pcap_update_mac(rx_queues->queue[0].name,
-- 
2.51.0