linux-kernel - Re: [PATCH v3] Add virtio-input driver.

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Date:	Wed, 25 Mar 2015 06:36:11 +0100
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Gerd Hoffmann <kraxel@...hat.com>, virtio-dev@...ts.oasis-open.org,
	virtualization@...ts.linux-foundation.org,
	David Herrmann <dh.herrmann@...il.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	open list <linux-kernel@...r.kernel.org>,
	"open list:ABI/API" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v3] Add virtio-input driver.

On Tue, Mar 24, 2015 at 10:28:05AM -0700, Dmitry Torokhov wrote:
> > > > > +	err = input_register_device(vi->idev);
> > > > > +	if (err)
> > > > > +		goto err_input_register;
> > > > > +
> > > > > +	return 0;
> > > > > +
> > > > > +err_input_register:
> > > > 
> > > > > +	input_free_device(vi->idev);
> > > > 
> > > > At this point you can already get interrupts
> > > > since you called virtio_device_ready, and
> > > > getting events from a freed device likely won't
> > > > DTRT.
> > > 
> > > Right. I guess you want to mark the virtio device ready only after
> > > registering input device.
> > 
> > No that's broken since you can get events after this
> > point, and you won't be able to forward them.
> 
> Who cares?

virtio cares: guest will crash if you attempt to
kick virtqueue before device ready call.

> What makes these events needed compared to ones sent 1 ms
> earlier before we had input device registered?
> 
> But I guess if you can call virtio_device_ready/virtio_device_broken
> several times then the best option is putting them into input_dev->open
> and input_dev->close callbacks.
> 
> Thanks.
> -- 
> Dmitry
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