render/vulkan: add support for VK_EXT_external_memory_host

[emersion]

This would allow for non-blocking shm texture uploads.

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wlroots has migrated to gitlab.freedesktop.org. This issue has been moved to:

https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/3264

[jbeich]

Needs to be optional due to missing userptr on BSDs, see FreeBSDDesktop/kms-drm#197 (comment) and mesa!13162.

CC @unrelentingtech to check if radv is also affected.

[emersion]

Not all drivers implement the ext anyways, so yeah we'll make it optional.

[valpackett]

@jbeich yes, radv would be affected of course. We really should implement mmu notifiers already…

[ascent12]

This would allow for non-blocking shm texture uploads.

Isn't uploading stuff to the GPU just a normal command submission, that isn't blocking anyway? It just depends how you wait on the fence or whatever.
All I think this extension would allow is potentially skipping a copy of the client's contents into a staging buffer.

[emersion]

This memcpy is blocking:

wlroots/render/vulkan/texture.c

Line 97 in cc2ebd9

// write data into staging buffer span

The ext allows Vulkan to asynchronously perform that memcpy, but I think the staging buffer will stay since we need HOST_VISIBLE | HOST_COHERENT?