The cause for this policy was due to dynamic linker behavior which could have
resulted in the wrong symbols being used. However, this didn't occur in
practical usage of the dynamic linker. Also drivers exporting Vulkan
entrypoints was a useful behavior to enable testing and more flexible usage
that this policy actively interfered with.
Modify the loader to only use VK_ADD_DRIVER_FILES if
VK_DRIVER_FILES or VK_ICD_FILENAMES is not used.
This could have caused weird issues with systems where VK_DRIVER_FILES
was used to force drivers in a specific order/location for testing.
Resolves issue #871
Add "additive" environment variables for adding additional layer
paths or driver JSON files instead of replacing default ones.
Also, rename VK_ICD_FILENAMES to VK_DRIVER_FILES since we're trying
to remove references to ICDs because software driver implementations
of Vulkan aren't ICDs (but continue to support the old name as well).
Added documentation around these changes to reflect the new name and
the new variables.
If a meta layer which contains `override_paths` is active, all of the paths in
VK_LAYER_PATH are ignored when searchign for explicit layers. This may be changed
changed in the future but for now is better tested and documented.
Expand override layer documentation to include override_paths
Add Versioning and Activation Interactions section which details some of the
more complex rules around when a layer is activated or not.
The loader ICD ordering could be random on Linux based on using readdir
to find ICD manifest files. This can result in random behaviors as
applications that select only the first device can switch which device is
used. To resolve this, we now sort based on device type and then
internally to the types based on PCI bus information.
This also introduces a VK_LOADER_DEFAULT_DEVICE environment variable
that can be used to force a specific PCI device. This environment variable
is actually a duplicate of the MESA_VK_DEVICE_SELECT variable, which is
also looked for if the loader environment variable is not found.
Note, that at least one ICD must support it for the extension to be used at all.
So we only do the sorting if one ICD supports it.
Fixes part of #657
Define expected behavior for a well-behaved loader, layers, and drivers.
This has been reviewed with other companies so that when issues arise,
it is easy to clearly communicate where one of the components has failed
to properly behave.
Add warnings/errors in the loader output when cases of policy that can
be detected are noticed.
Add a section warning about possible issues with bundling the
Khronos loader with an application/engine.
Also, rename "desktop loader" to "Khronos loader" since it is now
used for more than the original desktop targets.
Add a section in the application documentation on how to debug possible
layer issues.
Also add a small note on why a layer may need to intercept pre-instance
functions.
Feedback from Khronos was that "Implementation" was for the entire
set of Vulkan components underlying the application (including the
loader, layers, and drivers). Instead, what I had been calling
implementation should be called "Driver" including software
implementations of Vulkan at that level.
Also update the LOADER_DEBUG option "implem" to take "driver" as well.
All images also updated.
Update the loader documentation in the following ways:
1. Move documentation to new "docs" folder"
2. Split LoaderAndLayerInterface.md into multiple docs to focus
on target audience:
- Top-Level LoaderInterfaceArchitecture.md
- Applications LoaderApplicationInterface.md
- Layers LoaderLayerInterface.md
- ICDs LoaderImplementationInterface.md
3. Upload newer images and their corresponding original Inkscape files.
4. Cleanup and update sections on Linux directory search
5. Add new sections to detail items missing
- VkConfig
- Handling undef Fuchsia
6. Language cleanup
Thanks to @charles-lunarg and @smcv for feedback and various section language
corrections.
