Draft: Add a VK_MESA_legacy_dma_buf_drm_format_modifier_query extension

[gfxstrand]

This extension provides a way to query a legacy Linux dma-buf for its embedded modifier. This is needed by emulation layers which implement OpenGL on top of Vulkan and need to interact with legacy window-system components as the X server. This extension is not intended for general-purpose use and modifiers should be passed explicitly between applications or components whenever possible.

[gfxstrand]

Both sides of the Mesa implementation are here: https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33932

[cubanismo]

There's an internal MR with an alternative solution for this. We should probably reconcile the two rather than have two separate solutions.

[gfxstrand]

There's an internal MR with an alternative solution for this. We should probably reconcile the two rather than have two separate solutions.

A quick search isn't finding it. Can you throw me a # or tag me on the internal one?

[gfxstrand]

I looked it up. That's a very different extension for solving a very different problem. Mechanically, the implementation of the two may end up being similar on some implementations but they're not the same at all. This extension exists to solve a problem you really only hit if you're either using Vulkan to write an X11 compositor or are somehow inside the X server itself (such as when Zink is used by the modesetting driver) and need to composite buffers coming from Mesa GL drivers.

[orowith2os]

are somehow inside the X server itself (such as when Zink is used by the modesetting driver) and need to composite buffers coming from Mesa GL drivers.

This is the case inside of Flatpak, where you may be using nouveau GL or a CPU renderer, or perhaps some other GL driver (in the case of a multi-gpu system).

Systems with several GPUs/drivers, especially mixed with containers, are funky :)