lib/repo-finder-mount: Ignore mounts which have a ‘system’ file system

For example, tmpfs or a cgroup file system. This is basically an
optimisation of the list of file systems we check for repositories,
since we would never expect any of these file systems to be capable of
containing a repository.

Depends on the new API from
https://bugzilla.gnome.org/show_bug.cgi?id=788927.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Closes: #1307
Approved by: cgwalters

src/libostree/ostree-repo-finder-mount.c

@@ -23,6 +23,7 @@
 #include "config.h"
 
 #include <gio/gio.h>
+#include <gio/gunixmounts.h>
 #include <glib.h>
 #include <glib-object.h>
 #include <libglnx.h>
@@ -355,6 +356,23 @@ ostree_repo_finder_mount_resolve_async (OstreeRepoFinder                  *finde
           continue;
         }
 
+#if GLIB_CHECK_VERSION(2, 55, 0)
+G_GNUC_BEGIN_IGNORE_DEPRECATIONS  /* remove once GLIB_VERSION_MAX_ALLOWED ≥ 2.56 */
+      g_autoptr(GUnixMountEntry) mount_entry = g_unix_mount_at (mount_root_path, NULL);
+
+      if (mount_entry != NULL &&
+          (g_unix_is_system_fs_type (g_unix_mount_get_fs_type (mount_entry)) ||
+           g_unix_is_system_device_path (g_unix_mount_get_device_path (mount_entry))))
+        {
+          g_debug ("Ignoring mount ‘%s’ as its file system type (%s) or device "
+                   "path (%s) indicate it’s a system mount.",
+                   mount_name, g_unix_mount_get_fs_type (mount_entry),
+                   g_unix_mount_get_device_path (mount_entry));
+          continue;
+        }
+G_GNUC_END_IGNORE_DEPRECATIONS
+#endif  /* GLib 2.56.0 */
+
       /* stat() the mount root so we can later check whether the resolved
        * repositories for individual refs are on the same device (to avoid the
        * symlinks for them pointing outside the mount root). */