Use XDG_DATA_DIRS instead of hardcoding /usr/share

When running nvidia-ctk on a system that uses a custom XDG_DATA_DIRS
environment variable value, the configuration files for `glvnd`,
`vulkan`, and `egl` fail to get passed through from the host to the
container. Reading from XDG_DATA_DIRS instead of hardcoding the default
value allows for finding said files so they can be mounted in the
container.

Signed-off-by: Jared Baur <jaredbaur@fastmail.com>

Author: jmbaur

internal/discover/graphics.go

@@ -59,12 +59,15 @@ func NewGraphicsMountsDiscoverer(logger logger.Interface, driver *root.Driver, n
 		},
 	)
 
+	searchPaths := []string{"/etc"}
+	searchPaths = append(searchPaths, xdgDataDirs()...)
+
 	jsonMounts := NewMounts(
 		logger,
 		lookup.NewFileLocator(
 			lookup.WithLogger(logger),
 			lookup.WithRoot(driver.Root),
-			lookup.WithSearchPaths("/etc", "/usr/share"),
+			lookup.WithSearchPaths(searchPaths...),
 		),
 		driver.Root,
 		[]string{
@@ -295,7 +298,7 @@ func newXorgDiscoverer(logger logger.Interface, driver *root.Driver, nvidiaCTKPa
 		lookup.NewFileLocator(
 			lookup.WithLogger(logger),
 			lookup.WithRoot(driver.Root),
-			lookup.WithSearchPaths("/usr/share"),
+			lookup.WithSearchPaths(xdgDataDirs()...),
 		),
 		driver.Root,
 		[]string{"X11/xorg.conf.d/10-nvidia.conf"},
@@ -371,3 +374,15 @@ func (s selectDeviceByPath) MountIsSelected(Mount) bool {
 func (s selectDeviceByPath) HookIsSelected(Hook) bool {
 	return true
 }
+
+// xdgDataDirs finds the paths as specified in the environment variable XDG_DATA_DIRS.
+// See https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html.
+func xdgDataDirs() []string {
+	dirs, exists := os.LookupEnv("XDG_DATA_DIRS")
+
+	if !exists || dirs == "" {
+		return []string{"/usr/local/share", "/usr/share"}
+	}
+
+	return filepath.SplitList(dirs, ":")
+}