[PATCH 5/6] net/tap: let kernel choose tun device name

[Stephen Hemminger <stephen@networkplumber.org>]

Assigning tun and tap index in DPDK tap device driver is racy and
fails if used with primary/secondary process model. Instead, use the
kernel feature of device wildcarding where if a name with %d is used
the kernel will fill in the next available device.

Reported-by: hfli@netitest.com
Fixes: 02f96a0a82d1 ("net/tap: add TUN/TAP device PMD")
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 drivers/net/tap/rte_eth_tap.c | 32 ++++++++++++++++----------------
 1 file changed, 16 insertions(+), 16 deletions(-)

diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
index 50d6729cb609..b836c1ae3d4e 100644
--- a/drivers/net/tap/rte_eth_tap.c
+++ b/drivers/net/tap/rte_eth_tap.c
@@ -79,9 +79,6 @@ static const char *valid_arguments[] = {
 	NULL
 };
 
-static unsigned int tap_unit;
-static unsigned int tun_unit;
-
 static char tuntap_name[8];
 
 static volatile uint32_t tap_trigger;	/* Rx trigger */
@@ -151,8 +148,6 @@ tun_alloc(struct pmd_internals *pmd, int is_keepalive)
 		IFF_TAP : IFF_TUN | IFF_POINTOPOINT;
 	strlcpy(ifr.ifr_name, pmd->name, IFNAMSIZ);
 
-	TAP_LOG(DEBUG, "ifr_name '%s'", ifr.ifr_name);
-
 	fd = open(TUN_TAP_DEV_PATH, O_RDWR);
 	if (fd < 0) {
 		TAP_LOG(ERR, "Unable to create %s interface", tuntap_name);
@@ -186,6 +181,13 @@ tun_alloc(struct pmd_internals *pmd, int is_keepalive)
 		goto error;
 	}
 
+	/*
+	 * Name passed to kernel might be wildcard like dtun%d
+	 * and need to find the resulting device.
+	 */
+	TAP_LOG(DEBUG, "Device name is '%s'", ifr.ifr_name);
+	strlcpy(pmd->name, ifr.ifr_name, RTE_ETH_NAME_MAX_LEN);
+
 	if (is_keepalive) {
 		/*
 		 * Detach the TUN/TAP keep-alive queue
@@ -1756,6 +1758,7 @@ eth_dev_tap_create(struct rte_vdev_device *vdev, char *tap_name,
 		TAP_LOG(ERR, "Unable to create %s interface", tuntap_name);
 		goto error_exit;
 	}
+	TAP_LOG(INFO, "allocated %s", pmd->name);
 
 	ifr.ifr_mtu = dev->data->mtu;
 	if (tap_ioctl(pmd, SIOCSIFMTU, &ifr, 1, LOCAL_AND_REMOTE) < 0)
@@ -1917,8 +1920,8 @@ set_interface_name(const char *key __rte_unused,
 		}
 		strlcpy(name, value, RTE_ETH_NAME_MAX_LEN);
 	} else {
-		snprintf(name, RTE_ETH_NAME_MAX_LEN, "%s%d",
-			 DEFAULT_TAP_NAME, tun_unit - 1);
+		snprintf(name, RTE_ETH_NAME_MAX_LEN, "%s%%d",
+			 DEFAULT_TAP_NAME);
 	}
 	return 0;
 }
@@ -2031,8 +2034,8 @@ rte_pmd_tun_probe(struct rte_vdev_device *dev)
 		return 0;
 	}
 
-	snprintf(tun_name, sizeof(tun_name), "%s%u",
-		 DEFAULT_TUN_NAME, tun_unit++);
+	snprintf(tun_name, sizeof(tun_name), "%s%%d",
+		 DEFAULT_TUN_NAME);
 
 	if (params && (params[0] != '\0')) {
 		TAP_LOG(DEBUG, "parameters (%s)", params);
@@ -2052,17 +2055,15 @@ rte_pmd_tun_probe(struct rte_vdev_device *dev)
 	}
 	pmd_link.link_speed = ETH_SPEED_NUM_10G;
 
-	TAP_LOG(DEBUG, "Initializing pmd_tun for %s as %s",
-		name, tun_name);
+	TAP_LOG(DEBUG, "Initializing pmd_tun for %s", name);
 
 	ret = eth_dev_tap_create(dev, tun_name, remote_iface, 0,
-		ETH_TUNTAP_TYPE_TUN);
+				 ETH_TUNTAP_TYPE_TUN);
 
 leave:
 	if (ret == -1) {
 		TAP_LOG(ERR, "Failed to create pmd for %s as %s",
 			name, tun_name);
-		tun_unit--; /* Restore the unit number */
 	}
 	rte_kvargs_free(kvlist);
 
@@ -2218,8 +2219,8 @@ rte_pmd_tap_probe(struct rte_vdev_device *dev)
 	}
 
 	speed = ETH_SPEED_NUM_10G;
-	snprintf(tap_name, sizeof(tap_name), "%s%u",
-		 DEFAULT_TAP_NAME, tap_unit++);
+	snprintf(tap_name, sizeof(tap_name),
+		 "%s%%d", DEFAULT_TAP_NAME);
 	memset(remote_iface, 0, RTE_ETH_NAME_MAX_LEN);
 
 	if (params && (params[0] != '\0')) {
@@ -2282,7 +2283,6 @@ rte_pmd_tap_probe(struct rte_vdev_device *dev)
 				rte_mp_action_unregister(TAP_MP_KEY);
 			tap_devices_count--;
 		}
-		tap_unit--;		/* Restore the unit number */
 	}
 	rte_kvargs_free(kvlist);
 
-- 
2.20.1