[PATCH v7 4/4] winevulkan: Implement VK_KHR_external_memory_win32 for images.

[Zebediah Figura (she/her)]

On 5/26/21 9:21 AM, Derek Lesho wrote:
> On 5/25/21 10:07 PM, Zebediah Figura (she/her) wrote:
> 
>>
>>>>
>>>> * Shared resources in d3d9-11, when using the OpenGL backend
>>>
>>> As mentioned, the EXT_external_objects extension exists, (
>>> https://www.khronos.org/registry/OpenGL/extensions/EXT/EXT_external_objects.txt
>>>
>>> ), which accepts and produces file descriptors compatible with the ones
>>> Vulkan produces and accepts.  The interactions here seem to be well
>>> defined.
>>
>> According to my reading, neither GL_EXT_external_objects nor
>> GL_EXT_external_objects_fd provide for export of an object from an
>> OpenGL context; they only allow importing objects created by Vulkan.
> 
> Yeah, from what I can see, openGL has no standard way to share memory
> across processes without the use of this extension and Vulkan.  I
> suspect this would be difficult due to all the user mode driver code
> protecting against invalid use of resources.  I think the most
> reasonable path forward is to create a Vulkan dummy object in wined3d,
> then import it into GL.  Of course, this would make shared resources
> unsupported for old GPUs and systems that don't support Vulkan, but the
> API is half a decade old at this point, and only GPUs from almost a
> decade ago don't support it.

There is no free software NVidia Vulkan driver, which is a rather 
glaring hole. There also exist cards released as recently as 2014 that 
don't support Vulkan. And in general, although it's sometimes convenient 
for the implementer to require the latest hardware, it's a rather mean 
thing to do to users.

Keep in mind that we need Direct3D shared resources for bug 44985, which 
affects a very long list of applications.

Now, with that in mind, two options I immediately see are:

* Create all contexts as shared. It's not clear to me whether this has 
negative consequences, however. It's also not clear to me whether this 
can be done across processes.

* Try to introduce an OpenGL extension that allows exporting file 
descriptors.

> 
> Alternatively we could get try to use platform-specific buffer sharing
> APIs like EGLStreams or GBM, or just support in-process shared resources
> through the eglCreateContext API, which allows the creation of "shared
> contexts", in which the GPU resources are shared.
> 
>>>>
>>>> * Shared resources between d3d9-12 devices, when using wined3d or
>>>> libvkd3d on Windows
>>> Putting aside how rare and questionable of a use-case this must be, I
>>> don't think this concerns any of my patches.  My future patches would
>>> provide a way for translation layers on wine to store metadata alongside
>>> the host handlers, it doesn't have any correspondence to Windows.  If
>>> you really wanted to (why?), you could probably create your own backing
>>> storage in a shared memory object and accept the caveats that come along
>>> with that.
>>
>> I suspect those of us who have worked with Direct3D for multiple
>> decades would take issue with "rare and questionable", but regardless,
>> part of the point here is to ask: *is* it possible to use a native set
>> of APIs, like perhaps the D3DKMT*() functions from gdi32, to share
>> resources? I.e. should the implementation live in gdi32 instead of
>> winevulkan/opengl32/wined3d? Just from a quick scan I see several
>> which look like the ones we want, and they're even documented.
> 
> Could you link these APIs so I can look further into them?  I conferred
> with Josh and he didn't find anything.

Sure, here are some APIs that look promising, and are documented:

* D3DKMTCreateAllocation()
* D3DKMTOpenResource()
* D3DKMTOpenResourceFromNtHandle()
* D3DKMTQueryResourceInfo()
* D3DKMTQueryResourceInfoFromNtHandle()

> 
> Also, if there are APIs which allow registering resources retrieved from
> Vulkan with certain metadata, winevulkan would still have roughly the
> same role.  The only difference would be in the translation layers,
> where instead of using IOCTLs on the HANDLEs to shared resources they
> have to get/set metadata, they would use some D3DKMT API you've found.

Well, broadly, yes, but it changes the way that this patch series should 
be structured and sent.

> 
>>
>>>>
>>>> I note your tests also don't seem very interesting; they only share
>>>> objects within the same device. Sharing objects across multiple
>>>> devices, and across multiple processes, strikes me as more interesting.
>>>
>>> In my opinion, given that the semantics for VK_KHR_external_memory_fd
>>> and VK_KHR_external_memory_win32 are so similar, I wonder how relevant
>>> such tests would be, it seems like the kind of thing the Vulkan CTS
>>> should add for testing drivers.
>>>
>>> I think the tests should be more for testing the properties of the
>>> HANDLEs we get, as this is what we are implementing ourselves. Maybe I
>>> should add more tests looking at the locations of the named objects in
>>> the NT directory, or tests relating to types of the objects and their
>>> access permissions.
>>>
>>>
>>
>> The point is more of a smoke test, because it's easy to get it wrong,
>> and not too hard to verify that we got it right.
>>
>> It'd also be nice to demonstrate what the behaviour of KMT handles is
>> across processes.
>>
> An in-process intra-device test tests the same amount of winevulkan
> behavior as a cross-process inter-device test.  All the implementation
> details of cross-process and cross-device sharing are handled on the
> host and through wineserver's well established HANDLE<->FD mapping.
> 

Is it really that hard just to add a test?