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

  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(-)
  

> On Jan 11, 2019, at 12:06 PM, Stephen Hemminger <stephen@networkplumber.org> wrote:
> 
> 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);

Is this one required to be INFO as you wanted to reduce log clutter? I am ok with it, but thought I would ask.
> 
> 	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);

I guess a short comment would be nice for the reader to know that this is a kernel feature syntax.
> 	}
> 	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);

Same here.
> 
> 	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
> 

Regards,
Keith