Vulkan allocator doesn't support implicit modifiers

[ids1024]

Running anvil --x11 in a Gnome X session, it seems to fail to allocate buffers (at least on this particular hardware/driver). Looking into it, it seems the only modifiers it find available are Invalid, meaning implicit modifiers, which is filtered out in filter_modifiers.

[i509VCB]

I believe that VK_EXT_image_drm_format_modifier does not support INVALID as a modifier per the following:

VkImageDrmFormatModifierExplicitCreateInfoEXT:

VUID-VkImageDrmFormatModifierExplicitCreateInfoEXT-drmFormatModifier-02264

drmFormatModifier must be compatible with the parameters in VkImageCreateInfo and its pNext chain, as determined by querying VkPhysicalDeviceImageFormatInfo2 extended with VkPhysicalDeviceImageDrmFormatModifierInfoEXT

VkImageDrmFormatModifierListCreateInfoEXT

VUID-VkImageDrmFormatModifierListCreateInfoEXT-pDrmFormatModifiers-02263

Each modifier in pDrmFormatModifiers must be compatible with the parameters in VkImageCreateInfo and its pNext chain, as determined by querying VkPhysicalDeviceImageFormatInfo2 extended with VkPhysicalDeviceImageDrmFormatModifierInfoEXT

These statements are quite simple: Only use modifiers supported by the format based on info you can query.

So then let's look at VkPhysicalDeviceImageDrmFormatModifierInfoEXT. This returns a list of VkDrmFormatModifierPropertiesEXT containing info for each modifier supported by a format.

Quoting from the description of VkDrmFormatModifierPropertiesEXT

The implementation must not return DRM_FORMAT_MOD_INVALID in drmFormatModifier.

This means that Vulkan at the moment must reject an invalid format modifier, or that using an invalid modifier is undefined behavior.