[PATCH weston] compositor-drm: Fix crash when setting up seat constrained by an output

[Ander Conselvan de Oliveira]

On 04/22/2014 08:22 PM, Neil Roberts wrote:
> It looks like this patch makes Weston crash on touch events.
>
> The device_added functions in udev-seat.c and libinput-seat.c try to use
> the output list in order to assign the output for the newly created
> device. These functions get called via udev_input_init so I guess that
> means this function and create_outputs now depend on each other making a
> chicken and egg situation. If the device_added function can't find an
> output for the new device then it defaults to first output in the list.
> However since this patch the output list is now empty at that point so
> it ends up with a garbage pointer for the output. When the input code
> tries to handle an absolute event (eg, a touch event) then it tries to
> get the width and height from the current mode of the output for the
> device but this is now garbage. For me with libinput this causes it to
> segfault whereas without libinput it gets garbage width and height
> values and causes a floating point exception later on.

Yeah, I guess I forgot to test with an unmapped touch screen. I think we 
can just leave the device->output set to NULL in that case, and then fix 
it when a first output is created. I'll send a patch to do this.

Thanks,
Ander

> I haven't looked any further to decide what's the best thing to do.
>
> - Neil
>
> Ander Conselvan de Oliveira <conselvan2 at gmail.com> writes:
>
>> From: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira at intel.com>
>>
>> Commit 58e15865 changed the parameters for udev_get_seat_by_name() to
>> receive a struct udev_input. However, when this gets called from
>> create_output_from_connector() during initialization, the input struct
>> is not yet initialized, leading to a crash. Previously, that function
>> would take only a pointer to the compositor.
>>
>> This patch fixes the crash by initializing input before creating any
>> outputs.
>>
>> https://bugs.freedesktop.org/show_bug.cgi?id=77503