Re: [dpdk-dev] [PATCH v2] net/tap: fix device removal when no queues exist

["Wiles, Keith" <keith.wiles@intel.com>]

> On May 17, 2018, at 2:47 AM, Ophir Munk <ophirmu@mellanox.com> wrote:
> 
> TAP device is created following its first queue creation. Multiple
> queues can be added or removed over time. In Linux terminology those
> are file descriptors which are opened or closed over time. As long as
> the number of opened file descriptors is positive - TAP device will
> appear as a Linux device. In case all queues are released (the
> equivalent of all file descriptors being closed) the TAP device will
> be removed. This can lead to abnormalities in different scenarios
> where the TAP device should exist even if all its queues are released.
> In order to make TAP existence independent of its number of queues -
> an extra file descriptor is opened on TAP creation and is closed on
> TAP closure. It's only purpose is to serve as a keep-alive mechanism
> for the TAP device.
> 
> Fixes: bf7b7f437b49 ("net/tap: create netdevice during probing")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Ophir Munk <ophirmu@mellanox.com>
> ---
> v1:
> Initial release
> v2:
> Reword commit message (a fixing patch)
> 
> drivers/net/tap/rte_eth_tap.c | 31 ++++++++++++++++++++++++-------
> drivers/net/tap/rte_eth_tap.h |  1 +
> 2 files changed, 25 insertions(+), 7 deletions(-)

I did not see where ka_fd is set to -1 at startup, just in case we fail before the first open attempt and possible hit the close code in the remove routine. I did not look at the complete driver, but I think it maybe reasonable to add that initial variable setup.

> 
> diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
> index c006d07..6901edc 100644
> --- a/drivers/net/tap/rte_eth_tap.c
> +++ b/drivers/net/tap/rte_eth_tap.c
> @@ -929,6 +929,15 @@ tap_dev_close(struct rte_eth_dev *dev)
> 		ioctl(internals->ioctl_sock, SIOCSIFFLAGS,
> 				&internals->remote_initial_flags);
> 	}
> +
> +	if (internals->ka_fd != -1) {
> +		close(internals->ka_fd);
> +		internals->ka_fd = -1;
> +	}
> +	/*
> +	 * Since TUN device has no more opened file descriptors
> +	 * it will be removed from kernel
> +	 */
> }
> 
> static void
> @@ -1561,13 +1570,18 @@ eth_dev_tap_create(struct rte_vdev_device *vdev, char *tap_name,
> 			rte_memcpy(&pmd->eth_addr, mac_addr, sizeof(*mac_addr));
> 	}
> 
> -	/* Immediately create the netdevice (this will create the 1st queue). */
> -	/* rx queue */
> -	if (tap_setup_queue(dev, pmd, 0, 1) == -1)
> -		goto error_exit;
> -	/* tx queue */
> -	if (tap_setup_queue(dev, pmd, 0, 0) == -1)
> +	/*
> +	 * Allocate a TUN device keep-alive file descriptor that will only be
> +	 * closed when the TUN device itself is closed or removed.
> +	 * This keep-alive file descriptor will guarantee that the TUN device
> +	 * exists even when all of its queues are closed
> +	 */
> +	pmd->ka_fd = tun_alloc(pmd);
> +	if (pmd->ka_fd < 0) {
> +		pmd->ka_fd = -1;
> +		TAP_LOG(ERR, "Unable to create %s interface", tuntap_name);
> 		goto error_exit;
> +	}
> 
> 	ifr.ifr_mtu = dev->data->mtu;
> 	if (tap_ioctl(pmd, SIOCSIFMTU, &ifr, 1, LOCAL_AND_REMOTE) < 0)
> @@ -1961,9 +1975,12 @@ rte_pmd_tap_remove(struct rte_vdev_device *dev)
> 
> 	close(internals->ioctl_sock);
> 	rte_free(eth_dev->data->dev_private);
> -
> 	rte_eth_dev_release_port(eth_dev);
> 
> +	if (internals->ka_fd != -1) {
> +		close(internals->ka_fd);
> +		internals->ka_fd = -1;
> +	}
> 	return 0;
> }
> 
> diff --git a/drivers/net/tap/rte_eth_tap.h b/drivers/net/tap/rte_eth_tap.h
> index babe42d..575dce4 100644
> --- a/drivers/net/tap/rte_eth_tap.h
> +++ b/drivers/net/tap/rte_eth_tap.h
> @@ -81,6 +81,7 @@ struct pmd_internals {
> 	struct rx_queue rxq[RTE_PMD_TAP_MAX_QUEUES]; /* List of RX queues */
> 	struct tx_queue txq[RTE_PMD_TAP_MAX_QUEUES]; /* List of TX queues */
> 	struct rte_intr_handle intr_handle;          /* LSC interrupt handle. */
> +	int ka_fd;                        /* keep-alive file descriptor */
> };
> 
> /* tap_intr.c */
> -- 
> 2.7.4
> 

Regards,
Keith