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From:   Jason Andryuk <jandryuk@gmail.com>
Date:   Wed, 1 Nov 2023 10:11:39 -0400
Message-ID: <CAKf6xpuJe6Cza6bow3QxDGf1viu0kish7Y8YRN8haXL1oEF3HA@mail.gmail.com>
Subject: Re: [PATCH v3] Input: xen-kbdfront - drop keys to shrink modalias
To:     linux-kernel@vger.kernel.org,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc:     Phillip Susi <phill@thesusis.net>, stable@vger.kernel.org,
        Mattijs Korpershoek <mkorpershoek@baylibre.com>,
        linux-input@vger.kernel.org
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Hi Dmitry,

Do you have any feedback or can you pick this up?

Thanks,
Jason

On Wed, Oct 11, 2023 at 3:34=E2=80=AFPM Jason Andryuk <jandryuk@gmail.com> =
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@vps.thesusis.net/T/
>
> Cc: Phillip Susi <phill@thesusis.net>
> Cc: stable@vger.kernel.org
> Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
> Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
> ---
> 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-k=
bdfront.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 =3D KEY_ESC; i < KEY_UNKNOWN; i++)
>                         __set_bit(i, kbd->keybit);
> -               for (i =3D KEY_OK; i < KEY_MAX; i++)
> +               /*
> +                * In theory we want to go KEY_OK..KEY_MAX, but that grow=
s the
> +                * modalias line too long.  There is a gap of buttons fro=
m
> +                * 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 =3D KEY_OK; i < BTN_DPAD_UP; i++)
> +                       __set_bit(i, kbd->keybit);
> +               for (i =3D KEY_ALS_TOGGLE; i <=3D KEY_BRIGHTNESS_MENU; i+=
+)
>                         __set_bit(i, kbd->keybit);
>
>                 ret =3D input_register_device(kbd);
> --
> 2.41.0
>