Re: [Xen-devel] [PATCH v3 2/2] Input: xen-kbdfront - allow better run-time configuration

[Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>]

On Wed, May 16, 2018 at 08:47:30PM +0300, Oleksandr Andrushchenko wrote:
> On 05/16/2018 08:15 PM, Dmitry Torokhov wrote:
> > Hi Oleksandr,
> > 
> > On Mon, May 14, 2018 at 05:40:29PM +0300, Oleksandr Andrushchenko wrote:
> > > @@ -211,93 +220,114 @@ static int xenkbd_probe(struct xenbus_device *dev,
> > >           if (!info->page)
> > >                   goto error_nomem;
> > > - /* Set input abs params to match backend screen res */
> > > - abs = xenbus_read_unsigned(dev->otherend,
> > > -                            XENKBD_FIELD_FEAT_ABS_POINTER, 0);
> > > - ptr_size[KPARAM_X] = xenbus_read_unsigned(dev->otherend,
> > > -                                           XENKBD_FIELD_WIDTH,
> > > -                                           ptr_size[KPARAM_X]);
> > > - ptr_size[KPARAM_Y] = xenbus_read_unsigned(dev->otherend,
> > > -                                           XENKBD_FIELD_HEIGHT,
> > > -                                           ptr_size[KPARAM_Y]);
> > > - if (abs) {
> > > -         ret = xenbus_write(XBT_NIL, dev->nodename,
> > > -                            XENKBD_FIELD_REQ_ABS_POINTER, "1");
> > > -         if (ret) {
> > > -                 pr_warn("xenkbd: can't request abs-pointer\n");
> > > -                 abs = 0;
> > > -         }
> > > - }
> > > + /*
> > > +  * The below are reverse logic, e.g. if the feature is set, then
> > > +  * do not expose the corresponding virtual device.
> > > +  */
> > > + with_kbd = !xenbus_read_unsigned(dev->nodename,
> > > +                                  XENKBD_FIELD_FEAT_DSBL_KEYBRD, 0);
> > > - touch = xenbus_read_unsigned(dev->nodename,
> > > -                              XENKBD_FIELD_FEAT_MTOUCH, 0);
> > > - if (touch) {
> > > + with_ptr = !xenbus_read_unsigned(dev->nodename,
> > > +                                  XENKBD_FIELD_FEAT_DSBL_POINTER, 0);
> > > +
> > > + /* Direct logic: if set, then create multi-touch device. */
> > > + with_mtouch = xenbus_read_unsigned(dev->nodename,
> > > +                                    XENKBD_FIELD_FEAT_MTOUCH, 0);
> > > + if (with_mtouch) {
> > >                   ret = xenbus_write(XBT_NIL, dev->nodename,
> > >                                      XENKBD_FIELD_REQ_MTOUCH, "1");
> > >                   if (ret) {
> > >                           pr_warn("xenkbd: can't request multi-touch");
> > > -                 touch = 0;
> > > +                 with_mtouch = 0;
> > >                   }
> > >           }
> > Does it make sense to still end up calling xenkbd_connect_backend() when
> > all interfaces (keyboard, pointer, and multitouch) are disabled? Should
> > we do:
> > 
> >     if (!(with_kbd || || with_ptr || with_mtouch))
> >             return -ENXIO;
> > 
> > ?
> It does make sense. Then we probably need to move all xenbus_read_unsigned
> calls to the very beginning of the .probe, so no memory allocations are made
> which will be useless if we return -ENXIO, e.g. something like
> 
> static int xenkbd_probe(struct xenbus_device *dev,
>                   const struct xenbus_device_id *id)
> {
>     int ret, i;
>     bool with_mtouch, with_kbd, with_ptr;
>     struct xenkbd_info *info;
>     struct input_dev *kbd, *ptr, *mtouch;
> 
> <read with_mtouch, with_kbd, with_ptr here>
> 
> if (!(with_kbd | with_ptr | with_mtouch))
>         return -ENXIO;
> 
> Does the above looks ok?

Yes. Another option is to keep the check where I suggested and do

        if (...) {
                ret = -ENXIO;
                goto error;
        }

Whichever you prefer is fine with me.

Thanks.

-- 
Dmitry

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