[Xcb] [RFC libxcb 0/5] Fix GE events from the ground up, leading to a full 64bit sequence API

[Keith Packard]

Daniel Martin <consume.noise at gmail.com> writes:

> Hi everyone,
>
> we need to fix GE events to be able to support extensions using such
> events properly. Atm. xcb_ge_event_t has the full_sequence field at the
> 32byte boundary, where it's not supposed to be, because GE events can be
> larger then 32byte.
>
> The XInput extension v2++ uses GE events, so it's a show stopper on the
> way to have a decent support for it.

For my DRI3 hacking, I did just stick the sequence number in the event
encoding:

  <event name="ConfigureNotify" number="0">
    <field type="CARD8" name="extension" />
    <field type="CARD32" name="length" />
    <field type="CARD16" name="evtype" enum="EventType" />
    <pad bytes="2" />
    <field type="EVENT" name="event" />
    <field type="WINDOW" name="window" />
    <field type="INT16" name="x" />
    <field type="INT16" name="y" />
    <field type="CARD16" name="width" />
    <field type="CARD16" name="height" />
    <field type="INT16" name="off_x" />
    <field type="INT16" name="off_y" />
    <field type="CARD32" name="full_sequence"/>
    <field type="CARD16" name="pixmap_width" />
    <field type="CARD16" name="pixmap_height" />
    <field type="CARD32" name="pixmap_flags" />
  </event>


> One hack would be to inject the full_sequence into GE event structures
> while generating the header files. But, that would expose the
> full_sequence in specific events, somewhere in the middle of the usual
> event data, which is not conform to any specification one can read about
> this specific event.

I don't think that would matter much, and would retain ABI/API
compatibility with the existing codebase. Certainly seems like the
easiest plan to me.

> Additionally, this injection would need to happen
> in c_client.py. Injecting it within xcbgen would force any user of
> xcbgen to handle the mistake that happened in libxcb.

I looked at hacking up the c_client.py script to do this but gave up and
just hacked my .xml file directly, which definitely didn't seem right.

> The commit messages may need some polishing. But, for now I would like
> get some comments on this. As those changes break API and ABI I'm sure
> there'll be some. ;)

I think I'd rather avoid the API/ABI breakage and just leave the
full_sequence where it lives today; it's a bit ugly, but applications
won't actually see it in source code.

-- 
keith.packard at intel.com
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