docs/LoaderDebugging.md - external/github.com/KhronosGroup/Vulkan-Loader - Git at Google

 <!-- markdownlint-disable MD041 -->
 [![Khronos Vulkan][1]][2]

 [1]: https://vulkan.lunarg.com/img/Vulkan_100px_Dec16.png "https://www.khronos.org/vulkan/"
 [2]: https://www.khronos.org/vulkan/

 # Debugging The Vulkan Desktop Loader <!-- omit from toc -->
 [![Creative Commons][3]][4]

 <!-- Copyright &copy; 2015-2023 LunarG, Inc. -->

 [3]: https://i.creativecommons.org/l/by-nd/4.0/88x31.png "Creative Commons License"
 [4]: https://creativecommons.org/licenses/by-nd/4.0/
 ## Table of Contents <!-- omit from toc -->

 - [Debugging Issues](#debugging-issues)
 - [Loader Logging](#loader-logging)
 - [Debugging Possible Layer Issues](#debugging-possible-layer-issues)
   - [Enable Layer Logging](#enable-layer-logging)
   - [Disable Layers](#disable-layers)
   - [Selectively Re-enable Layers](#selectively-re-enable-layers)
 - [Allow specific layers to be ignored by VK\_LOADER\_LAYERS\_DISABLE](#allow-specific-layers-to-be-ignored-by-vk_loader_layers_disable)
 - [Debugging Possible Driver Issues](#debugging-possible-driver-issues)
   - [Enable Driver Logging](#enable-driver-logging)
   - [Selectively Enable Specific Drivers](#selectively-enable-specific-drivers)

 ## Debugging Issues

 If your application is crashing or behaving weirdly, the loader provides
 several mechanisms for you to debug the issues.

 **NOTE**: This functionality is all specific to the desktop Vulkan loader and
 does not work for the Android loader.

 ## Loader Logging

 The Vulkan desktop loader has added logging functionality that can be enabled by
 using the `VK_LOADER_DEBUG` environment variable.
 The results will be output to the standard output, but will also be passed to
 any `VK_EXT_debug_utils` messengers present as well.
 The variable can be set to a comma-delimited list of debug level options which
 include:

   * error&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Report any errors encountered by
     the loader
   * warn&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Report any warnings encountered by
     the loader
   * info&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Report info-level
     messages generated by the loader
   * debug&nbsp;&nbsp;&nbsp;&nbsp;Report debug-level messages generated by the
     loader
   * layer&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Report all layer-specific messages
     generated by the loader
   * driver&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Report all driver-specific messages
     generated by the loader
   * all&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Report all
     messages generated by the loader (includes all of the above)

 If you're not sure where the issue comes from, at least set it to output all
 messages through the "info" level:

 ```
 set VK_LOADER_DEBUG=error,warn,info
 ```

 Then, you can search the list for any errors or warnings that might provide a
 hint at why you're seeing issues.

 For more info on enabling loader logging, refer to the
 [Enable Loader Debug Layer Output](LoaderApplicationInterface.md#enable-loader-debug-layer-output)
 and the
 [Table of Debug Environment Variables](LoaderInterfaceArchitecture.md#table-of-debug-environment-variables)
 below.

 ## Debugging Possible Layer Issues

 ### Enable Layer Logging

 If you suspect a layer issue, set the loader logging to specifically output
 layer messages in addition to warnings and errors:

 ```
 set VK_LOADER_DEBUG=error,warn,layer
 ```

 Most important layer messages should go out with error or warning levels set,
 but this will provide more layer-specific info as well such as:
   * What layers are found
   * Where they were found
   * If they are implicit, what environment variables can be used to disable them
   * If there is any incompatibility with a given layer, this could include:
     * The layer library file (.so/.dll) wasn't found
     * The layer library is the wrong bit-depth for the executing application
       (i.e. 32-bit vs 64-bit)
     * The layer itself doesn't support the application desired version of Vulkan
   * If any environment variables are disabling any layers

 For example, the output of the loader looking for implicit layers may look like
 the following:

 ```
 LAYER: Searching for layer manifest files
 LAYER:  In following locations:
 LAYER:   /home/${USER}/.config/vulkan/implicit_layer.d
 LAYER:   /etc/xdg/vulkan/implicit_layer.d
 LAYER:   /usr/local/etc/vulkan/implicit_layer.d
 LAYER:   /etc/vulkan/implicit_layer.d
 LAYER:   /home/${USER}/.local/share/vulkan/implicit_layer.d
 LAYER:   /home/${USER}/.local/share/flatpak/exports/share/vulkan/implicit_layer.d
 LAYER:   /var/lib/flatpak/exports/share/vulkan/implicit_layer.d
 LAYER:   /usr/local/share/vulkan/implicit_layer.d
 LAYER:   /usr/share/vulkan/implicit_layer.d
 LAYER:  Found the following files:
 LAYER:   /home/${USER}/.local/share/vulkan/implicit_layer.d/renderdoc_capture.json
 LAYER:   /home/${USER}/.local/share/vulkan/implicit_layer.d/steamfossilize_i386.json
 LAYER:   /home/${USER}/.local/share/vulkan/implicit_layer.d/steamfossilize_x86_64.json
 LAYER:   /home/${USER}/.local/share/vulkan/implicit_layer.d/steamoverlay_i386.json
 LAYER:   /home/${USER}/.local/share/vulkan/implicit_layer.d/steamoverlay_x86_64.json
 LAYER:   /usr/share/vulkan/implicit_layer.d/nvidia_layers.json
 LAYER:   /usr/share/vulkan/implicit_layer.d/VkLayer_MESA_device_select.json
 ```

 Then, the loading of layer libraries is reported similar to this:

 ```
 LAYER | DEBUG: Loading layer library libVkLayer_khronos_validation.so
 LAYER | INFO: Insert instance layer VK_LAYER_KHRONOS_validation (libVkLayer_khronos_validation.so)
 LAYER | DEBUG: Loading layer library libVkLayer_MESA_device_select.so
 LAYER | INFO: Insert instance layer VK_LAYER_MESA_device_select (libVkLayer_MESA_device_select.so)
 ```

 Finally, when the Vulkan instance is created, you can see the full instance
 call-chain from a functional standpoint with output like this:

 ```
 LAYER: vkCreateInstance layer callstack setup to:
 LAYER:  <Application>
 LAYER:    ||
 LAYER:  <Loader>
 LAYER:    ||
 LAYER:  VK_LAYER_MESA_device_select
 LAYER:      Type: Implicit
 LAYER:         Disable Env Var:  NODEVICE_SELECT
 LAYER:      Manifest: /usr/share/vulkan/implicit_layer.d/VkLayer_MESA_device_select.json
 LAYER:      Library:  libVkLayer_MESA_device_select.so
 LAYER:    ||
 LAYER:  VK_LAYER_KHRONOS_validation
 LAYER:      Type: Explicit
 LAYER:      Manifest: /usr/share/vulkan/explicit_layer.d/VkLayer_khronos_validation.json
 LAYER:      Library:  libVkLayer_khronos_validation.so
 LAYER:    ||
 LAYER:  <Drivers>
 ```

 In this scenario, two layers were used (the same two that were loaded earlier):
 * `VK_LAYER_MESA_device_select`
 * `VK_LAYER_KHRONOS_validation`

 This information now shows us that the `VK_LAYER_MESA_device_select` is loaded
 first, followed by `VK_LAYER_KHRONOS_validation` which will then continue into
 any available drivers.
 It also shows that `VK_LAYER_MESA_device_select` is an implicit layer which
 implies that it wasn't directly enabled by the application.
 On the other hand, `VK_LAYER_KHRONOS_validation` is shown as an explicit layer
 which indicates that it was likely enabled by the application.

 ### Disable Layers

 **NOTE:** This functionality is only available with Loaders built with version
 1.3.234 of the Vulkan headers and later.

 Sometimes, implicit layers can cause issues with an application.
 Because of this, the next step is to try to disable one or more of the listed
 implicit layers.
 You can use the filtering environment variables
 (`VK_LOADER_LAYERS_ENABLE` and `VK_LOADER_LAYERS_DISABLE`) to selectively enable
 or disable various layers.
 If you're not sure what to do, try disabling all implicit layers manually by
 setting `VK_LOADER_LAYERS_DISABLE` to `~implicit~`.

 ```
   set VK_LOADER_LAYERS_DISABLE=~implicit~
 ```

 This will disable all implicit layers and the loader will report any disabled
 layers to the logging output when layer logging is enabled in the following way:

 ```
 WARNING | LAYER:  Implicit layer "VK_LAYER_MESA_device_select" forced disabled because name matches filter of env var 'VK_LOADER_LAYERS_DISABLE'.
 WARNING | LAYER:  Implicit layer "VK_LAYER_AMD_switchable_graphics_64" forced disabled because name matches filter of env var 'VK_LOADER_LAYERS_DISABLE'.
 WARNING | LAYER:  Implicit layer "VK_LAYER_Twitch_Overlay" forced disabled because name matches filter of env var 'VK_LOADER_LAYERS_DISABLE'.
 ```

 ### Selectively Re-enable Layers

 **NOTE:** This functionality is only available with Loaders built with version
 1.3.234 of the Vulkan headers and later.

 When trying to diagnose problems caused by layers, it is useful to first disable
 all layers and re-enable each layer individually.
 If the problem reappears, then it is immediately clear which layer is the source
 of the issue.

 For example, from the above given list of disabled layers, let’s selectively
 re-enable one:

 ```
 set VK_LOADER_LAYERS_DISABLE=~implicit~
 set VK_LOADER_LAYERS_ENABLE=*AMD*
 ```

 This would keep both the "VK_LAYER_MESA_device_select" and
 "VK_LAYER_Twitch_Overlay" layers disabled, while enabling the
 "VK_LAYER_AMD_switchable_graphics_64" layer.
 If everything continues to work, then the evidence seems to suggest the issue is
 likely not related to the AMD layer.
 This would lead to enabling one other layer and trying again:

 ```
 set VK_LOADER_LAYERS_DISABLE=~implicit~
 set VK_LOADER_LAYERS_ENABLE=*AMD*,*twitch*
 ```

 And so forth.

 For more info on how to use the filtering environment variables, refer to the
 [Layer Filtering](LoaderLayerInterface.md#layer-filtering) section of the
 [LoaderLayerInterface](LoaderLayerInterface.md) document.

 ## Allow specific layers to be ignored by VK_LOADER_LAYERS_DISABLE

 **NOTE:** VK_LOADER_LAYERS_DISABLE is only available with Loaders built with version
 1.3.262 of the Vulkan headers and later.

 When using `VK_LOADER_LAYERS_DISABLE` to disable implicit layers, it is possible
 to allow specific layers to be enabled using `VK_LOADER_LAYERS_ENABLE`.
 However, this has the effect of *forcing* layers to be enabled, which is not
 always desired.
 Implicit layers have the ability to only be enabled when a layer specified
 environment variable is set, allow for context dependent enablement.
 `VK_LOADER_LAYERS_ENABLE` ignores that context.

 Thus, a different environment variable is needed: `VK_LOADER_LAYERS_ALLOW`

 The behavior of `VK_LOADER_LAYERS_ALLOW` is similar to `VK_LOADER_LAYERS_ENABLE`
 except that it does not force a layer to be enabled.
 The way to think about this environment variable is that every layer matching
 `VK_LOADER_LAYERS_ALLOW` is excluded from being forcibly disabled by
 `VK_LOADER_LAYERS_DISABLE`.
 this allows for implicit layers that are context dependent to be enabled
 depending on the relevant context instead of force enabling them.

 Example: Disable all implicit layers except for any layers that have steam or
 mesa in their name.
 ```
 set VK_LOADER_LAYERS_DISABLE=~implicit~
 set VK_LOADER_LAYERS_ALLOW=*steam*,*Mesa*
 ```

 ## Debugging Possible Driver Issues

 ### Enable Driver Logging

 **NOTE:** This functionality is only available with Loaders built with version
 1.3.234 of the Vulkan headers and later.

 If you suspect a driver issue, set the loader logging to specifically output
 driver messages:

 ```
 set VK_LOADER_DEBUG=error,warn,driver
 ```

 Most important driver messages should go out with error or warning levels set,
 but this will provide more driver-specific info as well such as:
   * What drivers are found
   * Where they were found
   * If there is any incompatibility with a given driver
   * If any environment variables are disabling any of the drivers

 For example, the output of the loader looking for drivers on a Linux system may
 look like the following (NOTE: additional spaces have been removed from the
 output for easier reading):

 ```
 DRIVER: Searching for driver manifest files
 DRIVER:    In following folders:
 DRIVER:       /home/$(USER)/.config/vulkan/icd.d
 DRIVER:       /etc/xdg/vulkan/icd.d
 DRIVER:       /etc/vulkan/icd.d
 DRIVER:       /home/$(USER)/.local/share/vulkan/icd.d
 DRIVER:       /home/$(USER)/.local/share/flatpak/exports/share/vulkan/icd.d
 DRIVER:       /var/lib/flatpak/exports/share/vulkan/icd.d
 DRIVER:       /usr/local/share/vulkan/icd.d
 DRIVER:       /usr/share/vulkan/icd.d
 DRIVER:    Found the following files:
 DRIVER:       /usr/share/vulkan/icd.d/intel_icd.x86_64.json
 DRIVER:       /usr/share/vulkan/icd.d/lvp_icd.x86_64.json
 DRIVER:       /usr/share/vulkan/icd.d/radeon_icd.x86_64.json
 DRIVER:       /usr/share/vulkan/icd.d/lvp_icd.i686.json
 DRIVER:       /usr/share/vulkan/icd.d/radeon_icd.i686.json
 DRIVER:       /usr/share/vulkan/icd.d/intel_icd.i686.json
 DRIVER:       /usr/share/vulkan/icd.d/nvidia_icd.json
 DRIVER: Found ICD manifest file /usr/share/vulkan/icd.d/intel_icd.x86_64.json, version "1.0.0"
 DRIVER: Found ICD manifest file /usr/share/vulkan/icd.d/lvp_icd.x86_64.json, version "1.0.0"
 DRIVER: Found ICD manifest file /usr/share/vulkan/icd.d/radeon_icd.x86_64.json, version "1.0.0"
 DRIVER: Found ICD manifest file /usr/share/vulkan/icd.d/lvp_icd.i686.json, version "1.0.0"
 DRIVER: Requested driver /usr/lib/libvulkan_lvp.so was wrong bit-type. Ignoring this JSON
 DRIVER: Found ICD manifest file /usr/share/vulkan/icd.d/radeon_icd.i686.json, version "1.0.0"
 DRIVER: Requested driver /usr/lib/libvulkan_radeon.so was wrong bit-type. Ignoring this JSON
 DRIVER: Found ICD manifest file /usr/share/vulkan/icd.d/intel_icd.i686.json, version "1.0.0"
 DRIVER: Requested driver /usr/lib/libvulkan_intel.so was wrong bit-type. Ignoring this JSON
 DRIVER: Found ICD manifest file /usr/share/vulkan/icd.d/nvidia_icd.json, version "1.0.0"
 ```

 Then when the application selects the device to use, you will see the Vulkan
 device call chain reported in the following way (NOTE: additional spaces have
 been removed from the output for easier reading):

 ```
 DRIVER: vkCreateDevice layer callstack setup to:
 DRIVER:    <Application>
 DRIVER:      ||
 DRIVER:    <Loader>
 DRIVER:      ||
 DRIVER:    <Device>
 DRIVER:        Using "Intel(R) UHD Graphics 630 (CFL GT2)" with driver: "/usr/lib64/libvulkan_intel.so"
 ```


 ### Selectively Enable Specific Drivers

 **NOTE:** This functionality is only available with Loaders built with version
 1.3.234 of the Vulkan headers and later.

 You can now use the filtering environment variables
 (`VK_LOADER_DRIVERS_SELECT` and `VK_LOADER_DRIVERS_DISABLE`) to control what
 drivers the loader will attempt to load.
 For drivers, the string globs passed into the above environment variables will
 be compared against the driver JSON file name since there is no driver name
 known to the loader until much later in the Vulkan initialization process.

 For example, to disable all drivers except Nvidia you could do the following:

 ```
 set VK_LOADER_DRIVERS_DISABLE=*
 set VK_LOADER_DRIVERS_SELECT=*nvidia*
 ```

 The loader outputs messages like the following when the environment variables
 are used:

 ```
 WARNING | DRIVER: Driver "intel_icd.x86_64.json" ignored because not selected by env var 'VK_LOADER_DRIVERS_SELECT'
 WARNING | DRIVER: Driver "radeon_icd.x86_64.json" ignored because it was disabled by env var 'VK_LOADER_DRIVERS_DISABLE'
 ```

 For more info on how to use the filtering environment variables, refer to the
 [Driver Filtering](LoaderDriverInterface.md#driver-filtering) section of the
 [LoaderDriverInterface](LoaderDriverInterface.md) document.
	<!-- markdownlint-disable MD041 -->
	[![Khronos Vulkan][1]][2]

	[1]: https://vulkan.lunarg.com/img/Vulkan_100px_Dec16.png "https://www.khronos.org/vulkan/"
	[2]: https://www.khronos.org/vulkan/

	# Debugging The Vulkan Desktop Loader <!-- omit from toc -->
	[![Creative Commons][3]][4]

	<!-- Copyright © 2015-2023 LunarG, Inc. -->

	[3]: https://i.creativecommons.org/l/by-nd/4.0/88x31.png "Creative Commons License"
	[4]: https://creativecommons.org/licenses/by-nd/4.0/
	## Table of Contents <!-- omit from toc -->

	- [Debugging Issues](#debugging-issues)
	- [Loader Logging](#loader-logging)
	- [Debugging Possible Layer Issues](#debugging-possible-layer-issues)
	- [Enable Layer Logging](#enable-layer-logging)
	- [Disable Layers](#disable-layers)
	- [Selectively Re-enable Layers](#selectively-re-enable-layers)
	- [Allow specific layers to be ignored by VK\_LOADER\_LAYERS\_DISABLE](#allow-specific-layers-to-be-ignored-by-vk_loader_layers_disable)
	- [Debugging Possible Driver Issues](#debugging-possible-driver-issues)
	- [Enable Driver Logging](#enable-driver-logging)
	- [Selectively Enable Specific Drivers](#selectively-enable-specific-drivers)

	## Debugging Issues

	If your application is crashing or behaving weirdly, the loader provides
	several mechanisms for you to debug the issues.

	NOTE: This functionality is all specific to the desktop Vulkan loader and
	does not work for the Android loader.

	## Loader Logging

	The Vulkan desktop loader has added logging functionality that can be enabled by
	using the `VK_LOADER_DEBUG` environment variable.
	The results will be output to the standard output, but will also be passed to
	any `VK_EXT_debug_utils` messengers present as well.
	The variable can be set to a comma-delimited list of debug level options which
	include:

	* error      Report any errors encountered by
	the loader
	* warn      Report any warnings encountered by
	the loader
	* info        Report info-level
	messages generated by the loader
	* debug    Report debug-level messages generated by the
	loader
	* layer      Report all layer-specific messages
	generated by the loader
	* driver     Report all driver-specific messages
	generated by the loader
	* all          Report all
	messages generated by the loader (includes all of the above)

	If you're not sure where the issue comes from, at least set it to output all
	messages through the "info" level:

	```
	set VK_LOADER_DEBUG=error,warn,info
	```

	Then, you can search the list for any errors or warnings that might provide a
	hint at why you're seeing issues.

	For more info on enabling loader logging, refer to the
	[Enable Loader Debug Layer Output](LoaderApplicationInterface.md#enable-loader-debug-layer-output)
	and the
	[Table of Debug Environment Variables](LoaderInterfaceArchitecture.md#table-of-debug-environment-variables)
	below.

	## Debugging Possible Layer Issues

	### Enable Layer Logging

	If you suspect a layer issue, set the loader logging to specifically output
	layer messages in addition to warnings and errors:

	```
	set VK_LOADER_DEBUG=error,warn,layer
	```

	Most important layer messages should go out with error or warning levels set,
	but this will provide more layer-specific info as well such as:
	* What layers are found
	* Where they were found
	* If they are implicit, what environment variables can be used to disable them
	* If there is any incompatibility with a given layer, this could include:
	* The layer library file (.so/.dll) wasn't found
	* The layer library is the wrong bit-depth for the executing application
	(i.e. 32-bit vs 64-bit)
	* The layer itself doesn't support the application desired version of Vulkan
	* If any environment variables are disabling any layers

	For example, the output of the loader looking for implicit layers may look like
	the following:

	```
	LAYER: Searching for layer manifest files
	LAYER: In following locations:
	LAYER: /home/${USER}/.config/vulkan/implicit_layer.d
	LAYER: /etc/xdg/vulkan/implicit_layer.d
	LAYER: /usr/local/etc/vulkan/implicit_layer.d
	LAYER: /etc/vulkan/implicit_layer.d
	LAYER: /home/${USER}/.local/share/vulkan/implicit_layer.d
	LAYER: /home/${USER}/.local/share/flatpak/exports/share/vulkan/implicit_layer.d
	LAYER: /var/lib/flatpak/exports/share/vulkan/implicit_layer.d
	LAYER: /usr/local/share/vulkan/implicit_layer.d
	LAYER: /usr/share/vulkan/implicit_layer.d
	LAYER: Found the following files:
	LAYER: /home/${USER}/.local/share/vulkan/implicit_layer.d/renderdoc_capture.json
	LAYER: /home/${USER}/.local/share/vulkan/implicit_layer.d/steamfossilize_i386.json
	LAYER: /home/${USER}/.local/share/vulkan/implicit_layer.d/steamfossilize_x86_64.json
	LAYER: /home/${USER}/.local/share/vulkan/implicit_layer.d/steamoverlay_i386.json
	LAYER: /home/${USER}/.local/share/vulkan/implicit_layer.d/steamoverlay_x86_64.json
	LAYER: /usr/share/vulkan/implicit_layer.d/nvidia_layers.json
	LAYER: /usr/share/vulkan/implicit_layer.d/VkLayer_MESA_device_select.json
	```

	Then, the loading of layer libraries is reported similar to this:

	```
	LAYER \| DEBUG: Loading layer library libVkLayer_khronos_validation.so
	LAYER \| INFO: Insert instance layer VK_LAYER_KHRONOS_validation (libVkLayer_khronos_validation.so)
	LAYER \| DEBUG: Loading layer library libVkLayer_MESA_device_select.so
	LAYER \| INFO: Insert instance layer VK_LAYER_MESA_device_select (libVkLayer_MESA_device_select.so)
	```

	Finally, when the Vulkan instance is created, you can see the full instance
	call-chain from a functional standpoint with output like this:

	```
	LAYER: vkCreateInstance layer callstack setup to:
	LAYER: <Application>
	LAYER: \|\|
	LAYER: <Loader>
	LAYER: \|\|
	LAYER: VK_LAYER_MESA_device_select
	LAYER: Type: Implicit
	LAYER: Disable Env Var: NODEVICE_SELECT
	LAYER: Manifest: /usr/share/vulkan/implicit_layer.d/VkLayer_MESA_device_select.json
	LAYER: Library: libVkLayer_MESA_device_select.so
	LAYER: \|\|
	LAYER: VK_LAYER_KHRONOS_validation
	LAYER: Type: Explicit
	LAYER: Manifest: /usr/share/vulkan/explicit_layer.d/VkLayer_khronos_validation.json
	LAYER: Library: libVkLayer_khronos_validation.so
	LAYER: \|\|
	LAYER: <Drivers>
	```

	In this scenario, two layers were used (the same two that were loaded earlier):
	* `VK_LAYER_MESA_device_select`
	* `VK_LAYER_KHRONOS_validation`

	This information now shows us that the `VK_LAYER_MESA_device_select` is loaded
	first, followed by `VK_LAYER_KHRONOS_validation` which will then continue into
	any available drivers.
	It also shows that `VK_LAYER_MESA_device_select` is an implicit layer which
	implies that it wasn't directly enabled by the application.
	On the other hand, `VK_LAYER_KHRONOS_validation` is shown as an explicit layer
	which indicates that it was likely enabled by the application.

	### Disable Layers

	NOTE: This functionality is only available with Loaders built with version
	1.3.234 of the Vulkan headers and later.

	Sometimes, implicit layers can cause issues with an application.
	Because of this, the next step is to try to disable one or more of the listed
	implicit layers.
	You can use the filtering environment variables
	(`VK_LOADER_LAYERS_ENABLE` and `VK_LOADER_LAYERS_DISABLE`) to selectively enable
	or disable various layers.
	If you're not sure what to do, try disabling all implicit layers manually by
	setting `VK_LOADER_LAYERS_DISABLE` to `~implicit~`.

	```
	set VK_LOADER_LAYERS_DISABLE=~implicit~
	```

	This will disable all implicit layers and the loader will report any disabled
	layers to the logging output when layer logging is enabled in the following way:

	```
	WARNING \| LAYER: Implicit layer "VK_LAYER_MESA_device_select" forced disabled because name matches filter of env var 'VK_LOADER_LAYERS_DISABLE'.
	WARNING \| LAYER: Implicit layer "VK_LAYER_AMD_switchable_graphics_64" forced disabled because name matches filter of env var 'VK_LOADER_LAYERS_DISABLE'.
	WARNING \| LAYER: Implicit layer "VK_LAYER_Twitch_Overlay" forced disabled because name matches filter of env var 'VK_LOADER_LAYERS_DISABLE'.
	```

	### Selectively Re-enable Layers

	NOTE: This functionality is only available with Loaders built with version
	1.3.234 of the Vulkan headers and later.

	When trying to diagnose problems caused by layers, it is useful to first disable
	all layers and re-enable each layer individually.
	If the problem reappears, then it is immediately clear which layer is the source
	of the issue.

	For example, from the above given list of disabled layers, let’s selectively
	re-enable one:

	```
	set VK_LOADER_LAYERS_DISABLE=~implicit~
	set VK_LOADER_LAYERS_ENABLE=AMD
	```

	This would keep both the "VK_LAYER_MESA_device_select" and
	"VK_LAYER_Twitch_Overlay" layers disabled, while enabling the
	"VK_LAYER_AMD_switchable_graphics_64" layer.
	If everything continues to work, then the evidence seems to suggest the issue is
	likely not related to the AMD layer.
	This would lead to enabling one other layer and trying again:

	```
	set VK_LOADER_LAYERS_DISABLE=~implicit~
	set VK_LOADER_LAYERS_ENABLE=AMD,twitch
	```

	And so forth.

	For more info on how to use the filtering environment variables, refer to the
	[Layer Filtering](LoaderLayerInterface.md#layer-filtering) section of the
	[LoaderLayerInterface](LoaderLayerInterface.md) document.

	## Allow specific layers to be ignored by VK_LOADER_LAYERS_DISABLE

	NOTE: VK_LOADER_LAYERS_DISABLE is only available with Loaders built with version
	1.3.262 of the Vulkan headers and later.

	When using `VK_LOADER_LAYERS_DISABLE` to disable implicit layers, it is possible
	to allow specific layers to be enabled using `VK_LOADER_LAYERS_ENABLE`.
	However, this has the effect of forcing layers to be enabled, which is not
	always desired.
	Implicit layers have the ability to only be enabled when a layer specified
	environment variable is set, allow for context dependent enablement.
	`VK_LOADER_LAYERS_ENABLE` ignores that context.

	Thus, a different environment variable is needed: `VK_LOADER_LAYERS_ALLOW`

	The behavior of `VK_LOADER_LAYERS_ALLOW` is similar to `VK_LOADER_LAYERS_ENABLE`
	except that it does not force a layer to be enabled.
	The way to think about this environment variable is that every layer matching
	`VK_LOADER_LAYERS_ALLOW` is excluded from being forcibly disabled by
	`VK_LOADER_LAYERS_DISABLE`.
	this allows for implicit layers that are context dependent to be enabled
	depending on the relevant context instead of force enabling them.

	Example: Disable all implicit layers except for any layers that have steam or
	mesa in their name.
	```
	set VK_LOADER_LAYERS_DISABLE=~implicit~
	set VK_LOADER_LAYERS_ALLOW=steam,Mesa
	```

	## Debugging Possible Driver Issues

	### Enable Driver Logging

	NOTE: This functionality is only available with Loaders built with version
	1.3.234 of the Vulkan headers and later.

	If you suspect a driver issue, set the loader logging to specifically output
	driver messages:

	```
	set VK_LOADER_DEBUG=error,warn,driver
	```

	Most important driver messages should go out with error or warning levels set,
	but this will provide more driver-specific info as well such as:
	* What drivers are found
	* Where they were found
	* If there is any incompatibility with a given driver
	* If any environment variables are disabling any of the drivers

	For example, the output of the loader looking for drivers on a Linux system may
	look like the following (NOTE: additional spaces have been removed from the
	output for easier reading):

	```
	DRIVER: Searching for driver manifest files
	DRIVER: In following folders:
	DRIVER: /home/$(USER)/.config/vulkan/icd.d
	DRIVER: /etc/xdg/vulkan/icd.d
	DRIVER: /etc/vulkan/icd.d
	DRIVER: /home/$(USER)/.local/share/vulkan/icd.d
	DRIVER: /home/$(USER)/.local/share/flatpak/exports/share/vulkan/icd.d
	DRIVER: /var/lib/flatpak/exports/share/vulkan/icd.d
	DRIVER: /usr/local/share/vulkan/icd.d
	DRIVER: /usr/share/vulkan/icd.d
	DRIVER: Found the following files:
	DRIVER: /usr/share/vulkan/icd.d/intel_icd.x86_64.json
	DRIVER: /usr/share/vulkan/icd.d/lvp_icd.x86_64.json
	DRIVER: /usr/share/vulkan/icd.d/radeon_icd.x86_64.json
	DRIVER: /usr/share/vulkan/icd.d/lvp_icd.i686.json
	DRIVER: /usr/share/vulkan/icd.d/radeon_icd.i686.json
	DRIVER: /usr/share/vulkan/icd.d/intel_icd.i686.json
	DRIVER: /usr/share/vulkan/icd.d/nvidia_icd.json
	DRIVER: Found ICD manifest file /usr/share/vulkan/icd.d/intel_icd.x86_64.json, version "1.0.0"
	DRIVER: Found ICD manifest file /usr/share/vulkan/icd.d/lvp_icd.x86_64.json, version "1.0.0"
	DRIVER: Found ICD manifest file /usr/share/vulkan/icd.d/radeon_icd.x86_64.json, version "1.0.0"
	DRIVER: Found ICD manifest file /usr/share/vulkan/icd.d/lvp_icd.i686.json, version "1.0.0"
	DRIVER: Requested driver /usr/lib/libvulkan_lvp.so was wrong bit-type. Ignoring this JSON
	DRIVER: Found ICD manifest file /usr/share/vulkan/icd.d/radeon_icd.i686.json, version "1.0.0"
	DRIVER: Requested driver /usr/lib/libvulkan_radeon.so was wrong bit-type. Ignoring this JSON
	DRIVER: Found ICD manifest file /usr/share/vulkan/icd.d/intel_icd.i686.json, version "1.0.0"
	DRIVER: Requested driver /usr/lib/libvulkan_intel.so was wrong bit-type. Ignoring this JSON
	DRIVER: Found ICD manifest file /usr/share/vulkan/icd.d/nvidia_icd.json, version "1.0.0"
	```

	Then when the application selects the device to use, you will see the Vulkan
	device call chain reported in the following way (NOTE: additional spaces have
	been removed from the output for easier reading):

	```
	DRIVER: vkCreateDevice layer callstack setup to:
	DRIVER: <Application>
	DRIVER: \|\|
	DRIVER: <Loader>
	DRIVER: \|\|
	DRIVER: <Device>
	DRIVER: Using "Intel(R) UHD Graphics 630 (CFL GT2)" with driver: "/usr/lib64/libvulkan_intel.so"
	```


	### Selectively Enable Specific Drivers

	NOTE: This functionality is only available with Loaders built with version
	1.3.234 of the Vulkan headers and later.

	You can now use the filtering environment variables
	(`VK_LOADER_DRIVERS_SELECT` and `VK_LOADER_DRIVERS_DISABLE`) to control what
	drivers the loader will attempt to load.
	For drivers, the string globs passed into the above environment variables will
	be compared against the driver JSON file name since there is no driver name
	known to the loader until much later in the Vulkan initialization process.

	For example, to disable all drivers except Nvidia you could do the following:

	```
	set VK_LOADER_DRIVERS_DISABLE=*
	set VK_LOADER_DRIVERS_SELECT=nvidia
	```

	The loader outputs messages like the following when the environment variables
	are used:

	```
	WARNING \| DRIVER: Driver "intel_icd.x86_64.json" ignored because not selected by env var 'VK_LOADER_DRIVERS_SELECT'
	WARNING \| DRIVER: Driver "radeon_icd.x86_64.json" ignored because it was disabled by env var 'VK_LOADER_DRIVERS_DISABLE'
	```

	For more info on how to use the filtering environment variables, refer to the
	[Driver Filtering](LoaderDriverInterface.md#driver-filtering) section of the
	[LoaderDriverInterface](LoaderDriverInterface.md) document.