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

[Xiao Liang]

Thanks, Boris

Please see my reply inline.


On 07/28/2018 02:40 AM, Boris Ostrovsky wrote:
> 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@xxxxxxxxxx>
> > ---
> >   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?
In my understanding, netback_changed handles it if dev state is in 
XenbusStateInitialising and otherend is in XenbusStateInitWait, and then 
create connection to backend.
But in most cases, it breaks out as dev->state not in 
XenbusStateInitialising. So I added a wait here.
> And what about other states --- is,
> for example, XenbusStateClosing a valid reason to continue?
I think XenbusStateClosing should not be a valid reason to continue.
My purpose is waiting otherend status to be XenbusStateInitWait(after 
new dev created).To avoid unnecessary impact, IÂ only check it leaves 
closed and unknow state in this patch.

In my testing, hotplug vifs from guest in host or load/unload module in 
guest over 100 times, only waiting XenbusStateInitWait or as this patch 
does, both are working.
vifs can be created each time successfully.

Thanks,
Xiao Liang

> -boris
>
>
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