Consistent loader device ordering

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

BUILD.gn

@@ -181,6 +181,12 @@ if (!is_android) {
       }
       libs = [ "Cfgmgr32.lib" ]
     }
+    if (is_linux) {
+      sources += [
+        "loader/loader_linux.c",
+        "loader/loader_linux.h",
+      ]
+    }
     if (is_mac) {
       frameworks = [ "CoreFoundation.framework" ]
     }

docs/LoaderApplicationInterface.md

@@ -43,6 +43,7 @@
   * [Instance and Device Extensions](#instance-and-device-extensions)
   * [WSI Extensions](#wsi-extensions)
   * [Unknown Extensions](#unknown-extensions)
+* [Physical Device Ordering](#physical-device-ordering)
 
 ## Overview
 
@@ -888,5 +889,38 @@ variable to a non-zero number.
 This will effectively disable the loader's filtering of instance extension
 names.
 
+## Physical Device Ordering
+
+Prior to the 1.2.204 loader, physical devices on Linux could be returned in an
+inconsistent order.
+To remedy this, the Vulkan loader will now sort devices once they have been
+received from the drivers (before returning the information to any enabled
+layers) in the following fashion:
+ * Sort based on device type (Discrete, Integrated, Virtual, all others)
+ * Sort internal to the types based on PCI information (Domain, Bus, Device, and
+   Function).
+
+This allows for a consistent physical device order from run to run on the same
+system, unless the actual underlying hardware changes.
+
+A new environment variable is defined to give users the ability to force a
+specific device, `VK_LOADER_DEVICE_SELECT`.
+This environment variable should be set to the desired devices hex value for
+Vendor Id and Device Id (as returned from `vkGetPhysicalDeviceProperties` in
+the `VkPhysicalDeviceProperties` structure).
+It should look like the following:
+
+```
+set VK_LOADER_DEVICE_SELECT=0x10de:0x1f91
+```
+
+This will force on the device with a vendor ID of "0x10de" and a device ID
+of "0x1f91".
+If that device is not found, this is simply ignored.
+
+All device selection work done in the loader can be disabled by setting the
+environment variable `VK_LOADER_DISABLE_SELECT` to a non-zero value.
+This is intended for debug purposes to narrow down any issues with the loader
+device selection mechanism, but can be used by others.
 
 [Return to the top-level LoaderInterfaceArchitecture.md file.](LoaderInterfaceArchitecture.md)

docs/LoaderInterfaceArchitecture.md

@@ -515,6 +515,27 @@ discovery.
         &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;path_a&gt;;&lt;path_b&gt;</small>
     </td>
   </tr>
+  <tr>
+    <td><small><i>VK_LOADER_DEVICE_SELECT</i></small></td>
+    <td><b>Linux Only</b><br/>
+        Allows the user to force a particular device to be prioritized above all
+        other devices in the return order of <i>vkGetPhysicalDevices<i> and
+        <i>vkGetPhysicalDeviceGroups<i> functions.<br/>
+        The value should be "<hex vendor id>:<hex device id>".<br/>
+        <b>NOTE:</b> This not remove devices.
+    </td>
+    <td><small>set VK_LOADER_DEVICE_SELECT=0x10de:0x1f91</small>
+    </td>
+  </tr>
+  <tr>
+    <td><small><i>VK_LOADER_DISABLE_SELECT</i></small></td>
+    <td><b>Linux Only</b><br/>
+        Allows the user to disable the consistent sorting algorithm run in the
+        loader before returning the set of physical devices to layers.<br/>
+    </td>
+    <td><small>set VK_LOADER_DISABLE_SELECT=1</small>
+    </td>
+  </tr>
   <tr>
     <td><small><i>VK_LOADER_DISABLE_INST_EXT_FILTER</i></small></td>
     <td>Disable the filtering out of instance extensions that the loader doesn't

loader/CMakeLists.txt

@@ -160,6 +160,9 @@ set(NORMAL_LOADER_SRCS
 
 if(WIN32)
     set(NORMAL_LOADER_SRCS ${NORMAL_LOADER_SRCS} loader_windows.c)
+else(UNIX AND NOT APPLE) # i.e.: Linux
+    set(NORMAL_LOADER_SRCS ${NORMAL_LOADER_SRCS} loader_linux.c)
+    set_property(DIRECTORY APPEND PROPERTY COMPILE_DEFINITIONS LOADER_ENABLE_LINUX_SORT)
 endif()
 
 set(OPT_LOADER_SRCS dev_ext_trampoline.c phys_dev_ext.c)