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

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Message-ID: <1427197581.18768.16.camel@nilsson.home.kraxel.org>
Date:	Tue, 24 Mar 2015 12:46:21 +0100
From:	Gerd Hoffmann <kraxel@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	virtio-dev@...ts.oasis-open.org,
	virtualization@...ts.linux-foundation.org,
	David Herrmann <dh.herrmann@...il.com>,
	Dmitry Torokhov <dmitry.torokhov@...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: [virtio-dev] Re: [PATCH v3] Add virtio-input driver.

  Hi,

> > +	spin_lock_irqsave(&vi->lock, flags);
> > +	while ((event = virtqueue_get_buf(vi->evt, &len)) != NULL) {
> > +		input_event(vi->idev,
> > +			    le16_to_cpu(event->type),
> > +			    le16_to_cpu(event->code),
> > +			    le32_to_cpu(event->value));
> 
> What happens if input layer gets an
> unexpected event code or value?

input layer checks it and ignores events not supported (according to the
support bitmaps).

> > +static int virtinput_send_status(struct virtio_input *vi,
> > +				 u16 type, u16 code, s32 value)
> > +{

> This means that caller will get errors if it happens to call
> send_status at a rate that's faster than host's consumption of them.
> To me this looks wrong.
> Poking at input layer, it seems to simply discard errors.
> Is it always safe to discard status updates?

Typical use case is updating the leds of your keyboard.  Loosing one
update isn't the end of the world.  Also that are _very_ low rate
events, and in case that really actually happens you likely have bigger
problems anyway ;)

> > +static void virtinput_cfg_bits(struct virtio_input *vi, int select, int subsel,
> > +			       unsigned long *bits, unsigned int bitcount)
> > +{
> > +	unsigned int bit;
> > +	size_t bytes;
> > +	u8 *virtio_bits;
> > +
> > +	bytes = virtinput_cfg_select(vi, select, subsel);
> > +	if (!bytes)
> > +		return;
> 
> How about limiting bytes to sizeof struct virtio_input_config->u?

It's limited to 256 anyway because size is u8 in config space.

> > +	size = virtinput_cfg_select(vi, VIRTIO_INPUT_CFG_ID_DEVIDS, 0);
> > +	if (size >= 8) {
> 
> What does 8 mean here? Should be sizeof virtio_input_devids?

Yes, fixed.

> > +struct virtio_input_config {
> > +	__u8    select;
> > +	__u8    subsel;
> > +	__u8    size;
> > +	__u8    reserved;
> > +	union {
> > +		char string[128];
> > +		__u8 bitmap[128];
> 
> I note that neither string nor bitmap are used by
> driver. What are they in aid of?

Fixed.  Just sloppy coding, the name should use u.string, the bitmap
u.bitmap, instead of just "u" (although for offsetof it doesn't make a
difference).

cheers,
  Gerd


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