Re: [RFC/RFT] Reinject Alt+SysRq when no hotkeys have been pressed

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Thu, Nov 11, 2010 at 08:35:31AM -0600, Jason Wessel wrote:
> On 11/11/2010 02:55 AM, Dmitry Torokhov wrote:
> > On Wed, Nov 10, 2010 at 05:42:41PM -0800, Dmitry Torokhov wrote:
> >> On Wed, Nov 10, 2010 at 02:43:31PM -0600, Jason Wessel wrote:
> >>> On 11/10/2010 02:27 PM, Dmitry Torokhov wrote:
> >>>> On Wednesday, November 10, 2010 12:13:20 pm Jason Wessel wrote:
> >>>>> On 11/09/2010 01:34 AM, Dmitry Torokhov wrote:
> >>>>>> Now that KGDB knows how to release keys that have been pressed when
> >>>>>> entering the debugger the only issue left is that SysRq handler is too
> >>>>>> greedy and always swallows Alt+SysRq, causing print screen hotkey to
> >>>>>> stop working. The solution is to re-inject the key combo when user
> >>>>>> releases SysRq without pressing any other keys. The patch below does
> >>>>>> just that and also releases keys that have been pressed before we enter
> >>>>>> SysRq mode.
> >>>>>>
> >>>>>> Note that it depends on a patch to input core that will stop events
> >>>>>> injected by one input handler from reaching the very same input handler
> >>>>>> (attached).
> >>>>>>
> >>>>>> Comments/testing/suggestion are sought after.
> >>>>> I applied both patches and tested all the known failures cases I had on
> >>>>> my list and it looks good, for the non kdb cases.
> >>>>>
> >>>>> Tested-by: Jason Wessel <jason.wessel@windriver.com>
> >>>>>
> >>>>> However...  I also tested this with the kdb keyboard release
> >>>>> patches plus your latest 2 patches and we appear to have an
> >>>>> incompatibility.  The behavior is that when exiting kdb the print
> >>>>> screen trigger fires.  I had not had a chance to debug it as of
> >>>>> yet.
> >>>>>
> >>>> Hmm, let me think...
> >>>>
> >>> So I debugged it.  The key up events are peeled off in linear order
> >>> with the kdb release key code.
> >>>
> >>> The sequence looks like this
> >>>
> >>> down - alt
> >>> down - printScr
> >>> down - g           <-- Enters kdb
> >>>
> >>> The kdb release code simulates the events
> >>> up - g
> >>> up - alt
> >>> up - printScr
> >>>
> >>> That tells me we have something bad about the key events going on, or
> >>> that we care about release ordering in the release handler.
> >>>
> >> Ah, I see. I bet the shortcut for print screen is actually triggered on
> >> _release_ and X drivers do not filter release events for which they have
> >> not seen presses. Oh well...
> 
> That is in fact what was happening, and I probably should have
> mentioned that it was print screen handler that was trigging.
> 
> I tested you new patch with the prior sequence as well as the one that
> worked before which was:
> 
> down - alt down - sysrq up - sysrq down - g
> 
> Both sequences work as desired with the latest patch.
> 

Great, thank you for testing it.

> 
> I imagine we want to put this into a pull request for 37 as it is a
> regression, not being able to use alt-printScreen for the desktop
> OS's.
> 
> Acked-by: Jason Wessel <jason.wessel@windriver.com>
>

Yes, I agree, I will try to get it in, maybe not in the next pull
request but in the following one.

-- 
Dmitry