Re: [PATCH v2] Input: xen-kbdfront - drop keys to shrink modalias

[Mattijs Korpershoek <mkorpershoek@xxxxxxxxxxxx>]

On Fri, Dec 09, 2022 at 09:26, 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>

> ---
>  drivers/input/misc/xen-kbdfront.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> v2:
> Remove more keys: v1 didn't remove enough and modalias was still broken.
>
> diff --git a/drivers/input/misc/xen-kbdfront.c 
> b/drivers/input/misc/xen-kbdfront.c
> index 8d8ebdc2039b..4ecb579df748 100644
> --- a/drivers/input/misc/xen-kbdfront.c
> +++ b/drivers/input/misc/xen-kbdfront.c
> @@ -256,7 +256,14 @@ 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);
> -- 
> 2.38.1