Re: [PATCH v3] Input: xen-kbdfront - drop keys to shrink modalias

[Jason Andryuk]

Hi Dmitry,

Do you have any feedback, or can you pick up this patch?  It solves a
real issue affecting udev, which crashes the Debian installer and
breaks the mouse for Gnome.

Or would you be okay if this patch went in via the Xen tree?

Thanks,
Jason

On Wed, Nov 1, 2023 at 10:11 AM Jason Andryuk <jandryuk@xxxxxxxxx> wrote:
>
> Hi Dmitry,
>
> Do you have any feedback or can you pick this up?
>
> Thanks,
> Jason
>
> On Wed, Oct 11, 2023 at 3:34 PM Jason Andryuk <jandryuk@xxxxxxxxx> wrote:
> >
> > xen kbdfront registers itself as being able to deliver *any* key since
> > it doesn't know what keys the backend may produce.
> >
> > Unfortunately, the generated modalias gets too large and uevent creation
> > fails with -ENOMEM.
> >
> > This can lead to gdm not using the keyboard since there is no seat
> > associated [1] and the debian installer crashing [2].
> >
> > Trim the ranges of key capabilities by removing some BTN_* ranges.
> > While doing this, some neighboring undefined ranges are removed to trim
> > it further.
> >
> > An upper limit of KEY_KBD_LCD_MENU5 is still too large.  Use an upper
> > limit of KEY_BRIGHTNESS_MENU.
> >
> > This removes:
> > BTN_DPAD_UP(0x220)..BTN_DPAD_RIGHT(0x223)
> > Empty space 0x224..0x229
> >
> > Empty space 0x28a..0x28f
> > KEY_MACRO1(0x290)..KEY_MACRO30(0x2ad)
> > KEY_MACRO_RECORD_START          0x2b0
> > KEY_MACRO_RECORD_STOP           0x2b1
> > KEY_MACRO_PRESET_CYCLE          0x2b2
> > KEY_MACRO_PRESET1(0x2b3)..KEY_MACRO_PRESET3(0xb5)
> > Empty space 0x2b6..0x2b7
> > KEY_KBD_LCD_MENU1(0x2b8)..KEY_KBD_LCD_MENU5(0x2bc)
> > Empty space 0x2bd..0x2bf
> > BTN_TRIGGER_HAPPY(0x2c0)..BTN_TRIGGER_HAPPY40(0x2e7)
> > Empty space 0x2e8..0x2ff
> >
> > The modalias shrinks from 2082 to 1550 bytes.
> >
> > A chunk of keys need to be removed to allow the keyboard to be used.
> > This may break some functionality, but the hope is these macro keys are
> > uncommon and don't affect any users.
> >
> > [1] https://github.com/systemd/systemd/issues/22944
> > [2] https://lore.kernel.org/xen-devel/87o8dw52jc.fsf@xxxxxxxxxxxxxxxx/T/
> >
> > Cc: Phillip Susi <phill@xxxxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Jason Andryuk <jandryuk@xxxxxxxxx>
> > Reviewed-by: Mattijs Korpershoek <mkorpershoek@xxxxxxxxxxxx>
> > ---
> > v3:
> > Add Mattijs R-b
> > Put /* and */ on separate lines
> > ---
> >  drivers/input/misc/xen-kbdfront.c | 11 ++++++++++-
> >  1 file changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/input/misc/xen-kbdfront.c b/drivers/input/misc/xen-kbdfront.c
> > index 67f1c7364c95..d59ba8f9852e 100644
> > --- a/drivers/input/misc/xen-kbdfront.c
> > +++ b/drivers/input/misc/xen-kbdfront.c
> > @@ -256,7 +256,16 @@ static int xenkbd_probe(struct xenbus_device *dev,
> >                 __set_bit(EV_KEY, kbd->evbit);
> >                 for (i = KEY_ESC; i < KEY_UNKNOWN; i++)
> >                         __set_bit(i, kbd->keybit);
> > -               for (i = KEY_OK; i < KEY_MAX; i++)
> > +               /*
> > +                * In theory we want to go KEY_OK..KEY_MAX, but that grows the
> > +                * modalias line too long.  There is a gap of buttons from
> > +                * BTN_DPAD_UP..BTN_DPAD_RIGHT and KEY_ALS_TOGGLE is the next
> > +                * defined. Then continue up to KEY_BRIGHTNESS_MENU as an upper
> > +                * limit.
> > +                */
> > +               for (i = KEY_OK; i < BTN_DPAD_UP; i++)
> > +                       __set_bit(i, kbd->keybit);
> > +               for (i = KEY_ALS_TOGGLE; i <= KEY_BRIGHTNESS_MENU; i++)
> >                         __set_bit(i, kbd->keybit);
> >
> >                 ret = input_register_device(kbd);
> > --
> > 2.41.0
> >