xcb: list & padding

[Peter Harris]

>> https://gitlab.freedesktop.org/xorg/lib/libxcb/-/merge_requests/14 changes it so that lists always require explicit padding (and therefore allows unpadded lists). This MR is stalled. With a little review, I think it can be merged.
>
> oh, it's laying around there for 3 years now, nobody seems to care :(
> (needs rebase, btw)

Rebased.

> Do you think this would help for GetKbdByName() ?
> This one is a bit tricky: it has a bunch of variable-length fields
> (CARD8 size plus payload), and is _not_ padded.

Probably, since it deletes all the automatic pad insertion (except the
mandatory alignment pad at the very end). Feel free to try it out.

Note that new requests have been added to xcbproto since I wrote this patch,
and I haven't audited them to see if any expect automatic padding.

>> As long as you're looking at xkb, see also https://gitlab.freedesktop.org/xorg/proto/xcbproto/-/merge_requests/39
>
> Maybe split it into several pieces ?

Feel free to pick it up and run with it. Personally, I don't have the energy to
split it up, and I definitely don't have the energy (or the knowledge, if I'm
honest) to do the ABI bump or the necessary libxcb code generator fixes. That
MR is provided as-is, where-is, you get to keep all the broken bits. :-)

> Then we could check on per-case basis which ones are practically
> breaking (not just theoretically, because nobody uses those funcs)

Debian Codesearch is amazing, but it only searches what's in Debian.
Unfortunately, there's no way to really know what people are using in-house (or
wherever).

> Another idea is adding *new* calls (with same opcode) - I don't think
> that having the same opcode use multiple times should be really a major
> problem.

If you mean in libxcb, that is a good idea. Feel free to pick it up and run
with it.

If you mean in xcbproto, that's a bad idea. Wireshark (and etc) need exactly
one definition for each opcode.

Peter Harris
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