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

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Message-ID: <CAKf6xpvHa86frvOp5L3x1nerTCQD=cjz7xqR4VwFBExquKG5bw@mail.gmail.com>
Date:   Thu, 20 Oct 2022 08:21:27 -0400
From:   Jason Andryuk <jandryuk@...il.com>
To:     Mattijs Korpershoek <mkorpershoek@...libre.com>
Cc:     linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        Phillip Susi <phill@...susis.net>, stable@...r.kernel.org,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        linux-input@...r.kernel.org
Subject: Re: [PATCH] Input: xen-kbdfront - drop keys to shrink modalias

On Thu, Oct 20, 2022 at 4:31 AM Mattijs Korpershoek
<mkorpershoek@...libre.com> wrote:
>
> On Wed, Oct 19, 2022 at 16:14, Jason Andryuk <jandryuk@...il.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.
> >
> > This removes:
> > BTN_DPAD_UP(0x220)..BTN_DPAD_RIGHT(0x223)
> > Empty space 0x224..0x229
> >
> > Emtpy space 0x2bd..0x2bf
> > BTN_TRIGGER_HAPPY(0x2c0)..BTN_TRIGGER_HAPPY40(0x2e7)
> > Empty space 0x2e8..0x2ff
> >
> > The modalias shrinks from 2082 to 1754 bytes.
> >
> > [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@...susis.net>
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Jason Andryuk <jandryuk@...il.com>
>
> Reviewed-by: Mattijs Korpershoek <mkorpershoek@...libre.com>

This patch doesn't work and needs to be withdrawn.  My gdm/udev
workaround was still active when I tested, so that is why I had a
working keyboard.  Sorry about that.

Now the question is, which additional keys can be omitted to trim the
modalias to an acceptable size?

Regards,
Jason

> > ---
> >  drivers/input/misc/xen-kbdfront.c | 9 ++++++++-
> >  1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/input/misc/xen-kbdfront.c b/drivers/input/misc/xen-kbdfront.c
> > index 8d8ebdc2039b..23f37211be78 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.  KEY_KBD_LCD_MENU5 is the last
> > +              * defined non-button key. There is a gap of buttons from
> > +              * BTN_DPAD_UP..BTN_DPAD_RIGHT and KEY_ALS_TOGGLE is the next
> > +              * defined. */
> > +             for (i = KEY_OK; i < BTN_DPAD_UP; i++)
> > +                     __set_bit(i, kbd->keybit);
> > +             for (i = KEY_ALS_TOGGLE; i <= KEY_KBD_LCD_MENU5; i++)
> >                       __set_bit(i, kbd->keybit);
> >
> >               ret = input_register_device(kbd);
> > --
> > 2.37.3