Re: [Xen-devel][PATCH] xen/netfront: Remove unneeded .resume callback

[Oleksandr Andrushchenko]

On 3/14/19 5:02 PM, Boris Ostrovsky wrote:
> On 3/14/19 10:52 AM, Oleksandr Andrushchenko wrote:
> > On 3/14/19 4:47 PM, Boris Ostrovsky wrote:
> > > On 3/14/19 9:17 AM, Oleksandr Andrushchenko wrote:
> > > > From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> > > >
> > > > Currently on driver resume we remove all the network queues and
> > > > destroy shared Tx/Rx rings leaving the driver in its current state
> > > > and never signaling the backend of this frontend's state change.
> > > > This leads to the number of consequences:
> > > > - when frontend withdraws granted references to the rings etc. it
> > > > cannot
> > > >  ÂÂ be cleanly done as the backend still holds those (it was not told to
> > > >  ÂÂ free the resources)
> > > > - it is not possible to resume driver operation as all the
> > > > communication
> > > >  ÂÂ means with the backned were destroyed by the frontend, thus
> > > >  ÂÂ making the frontend appear to the guest OS as functional, but
> > > >  ÂÂ not really.
> > > What do you mean? Are you saying that after resume you lose
> > > connectivity?
> > Exactly, if you take a look at the .resume callback as it is now
> > what it does it destroys the rings etc. and never notifies the backend
> > of that, e.g. it stays in, say, connected state with communication
> > channels destroyed. It never goes into any other Xen bus state, so
> > there is
> > no way its state machine can help recovering.
>
> My tree is about a month old so perhaps there is some sort of regression
> but this certainly works for me. After resume netfront gets
> XenbusStateInitWait from backend which causes xennet_connect().
Ah, the difference can be of the way we get the guest enter
the suspend state. I am making my guest to suspend with:
echo mem > /sys/power/state
And then I use an interrupt to the guest (this is a test code)
to wake it up.
Could you please share your exact use-case when the guest enters suspend
and what you do to resume it?
I can see no way backend may want enter XenbusStateInitWait in my use-case
as it simply doesn't know we want him to.
> -boris
Thank you,
Oleksandr