HIDIOCKM[GS]DIRECT ioctls for the USB HID driver [PSARC/2009/329 FastTrack timeout 06/10/2009]

[Aaron Zang]

Aaron Zang wrote:
> Hi James,
>
>
> James Carlson wrote:
>> Garrett D'Amore - sun microsystems writes:
>>   
>>> To solve the above problem, two new HID ioctls are introduced:
>>>     
>>
>> Two questions:
>>
>>   - How do these ioctls solve the problem?  Who will issue the ioctls
>>     and under what conditions?  What happens if they're not used (if,
>>     for example, something kills the Xorg server)?
>>
>>   
>
> First, Xorg will open the hid devices upon startup. So the input goes 
> to Xorg.
> While switching back to console, Xorg is in charge of issuing the 
> ioctls to switch input
> to console since only Xorg has the context of which devices it keeps 
> opening.
>
> If something kills the Xorg server, the opened files will be closed, 
> so the input will
> automatically directed to the internal stream again.
>
>>   - Why not just send copies of the input to all open streams?
>>     Wouldn't that be simpler?
>>
>>   
>
> If we send the input to both the internal and external streams, when 
> you are on console
> again no matter by switching back or Xorg exits, all the input 
> characters typed under
> X will be shown on console, that would be messy.
>
Sorry, I was not 100% correct when trying to answer the latter question.
If all the input were sent to both the internal and external streams. 
The upper conskbd
 (virtual keyboard "/dev/kbd") would also get the input. If Xorg opens 
/dev/kbd which
is the case for now, Xorg will get 2 copies of input.
If Xorg does not open "/dev/kbd", console will get the input and echo 
back, that
would be the mess.

Actually we have already have a pair of similar ioctls (KIOC[GS]DIRECT]) 
to direct
the input in conskbd since conskbd also keeps 2 streams as you can see 
from the
diagram in the case material.

Regards,
Aaron