Re: [PATCH] xen-netfront: wait xenbus state change when load module manually

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 07/27/2018 05:56 AM, Xiao Liang wrote:
> When loading module manually, after call xenbus_switch_state to initializes
> the state of the netfront device, the driver state did not change so fast
> that may lead no dev created in latest kernel. This patch adds wait to make
> sure xenbus knows the driver is not in closed/unknown state.
>
> Current state:
> [vm]# ethtool eth0
> Settings for eth0:
> 	Link detected: yes
> [vm]# modprobe -r xen_netfront
> [vm]# modprobe  xen_netfront
> [vm]# ethtool eth0
> Settings for eth0:
> Cannot get device settings: No such device
> Cannot get wake-on-lan settings: No such device
> Cannot get message level: No such device
> Cannot get link status: No such device
> No data available
>
> With the patch installed.
> [vm]# ethtool eth0
> Settings for eth0:
> 	Link detected: yes
> [vm]# modprobe -r xen_netfront
> [vm]# modprobe xen_netfront
> [vm]# ethtool eth0
> Settings for eth0:
> 	Link detected: yes
>
> Signed-off-by: Xiao Liang <xiliang@redhat.com>
> ---
>  drivers/net/xen-netfront.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index a57daecf1d57..2d8812dd1534 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -87,6 +87,7 @@ struct netfront_cb {
>  /* IRQ name is queue name with "-tx" or "-rx" appended */
>  #define IRQ_NAME_SIZE (QUEUE_NAME_SIZE + 3)
>  
> +static DECLARE_WAIT_QUEUE_HEAD(module_load_q);
>  static DECLARE_WAIT_QUEUE_HEAD(module_unload_q);
>  
>  struct netfront_stats {
> @@ -1330,6 +1331,11 @@ static struct net_device *xennet_create_dev(struct xenbus_device *dev)
>  	netif_carrier_off(netdev);
>  
>  	xenbus_switch_state(dev, XenbusStateInitialising);
> +	wait_event(module_load_q,
> +			   xenbus_read_driver_state(dev->otherend) !=
> +			   XenbusStateClosed &&
> +			   xenbus_read_driver_state(dev->otherend) !=
> +			   XenbusStateUnknown);
>  	return netdev;
>  
>   exit:


Should we have a wake_up somewhere? And what about other states --- is,
for example, XenbusStateClosing a valid reason to continue?


-boris