[glib/settings-portal] Wip: add support for system defaults to keyfile backend

[Matthias Clasen <matthiasc src gnome org>]

commit 4dfa7979673e16067b14edd4b55821e9dea938a8
Author: Matthias Clasen <mclasen redhat com>
Date:   Mon Nov 5 16:07:55 2018 -0500

    Wip: add support for system defaults to keyfile backend
    
    Stacked databases and locks are dconf features that allow
    management software like Fleet Commander to set system-wide
    defaults and overrides centrally for applications.
    
    This proof-of-concept patch adds minimal support for the
    same to the keyfile settings backend. We read a system-wide
    keyfile and a list of locks (the current file locations are
    just for testing), and treat the values from the system-wide
    keyfile as overrides or defaults, depending on whether the
    key is on the list of locks or not. Writes always go to the
    per-user keyfile.

 gio/gkeyfilesettingsbackend.c | 79 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 78 insertions(+), 1 deletion(-)
---
diff --git a/gio/gkeyfilesettingsbackend.c b/gio/gkeyfilesettingsbackend.c
index ab214d3d4..c7512800e 100644
--- a/gio/gkeyfilesettingsbackend.c
+++ b/gio/gkeyfilesettingsbackend.c
@@ -60,6 +60,8 @@ typedef struct
   GKeyFile          *keyfile;
   GPermission       *permission;
   gboolean           writable;
+  GKeyFile          *system_keyfile;
+  GHashTable        *system_locks;
 
   gchar             *prefix;
   gint               prefix_len;
@@ -204,10 +206,19 @@ get_from_keyfile (GKeyfileSettingsBackend *kfsb,
   if (convert_path (kfsb, key, &group, &name))
     {
       gchar *str;
+      gchar *sysstr;
 
       g_assert (*name);
 
+      sysstr = g_key_file_get_value (kfsb->system_keyfile, group, name, NULL);
       str = g_key_file_get_value (kfsb->keyfile, group, name, NULL);
+      if (sysstr &&
+          (g_hash_table_contains (kfsb->system_locks, key) ||
+           str == NULL))
+        {
+          g_free (str);
+          str = g_strdup (sysstr);
+        }
 
       if (str)
         {
@@ -215,6 +226,8 @@ get_from_keyfile (GKeyfileSettingsBackend *kfsb,
           g_free (str);
         }
 
+      g_free (sysstr);
+
       g_free (group);
       g_free (name);
     }
@@ -229,6 +242,9 @@ set_to_keyfile (GKeyfileSettingsBackend *kfsb,
 {
   gchar *group, *name;
 
+  if (g_hash_table_contains (kfsb->system_locks, key))
+    return FALSE;
+
   if (convert_path (kfsb, key, &group, &name))
     {
       if (value)
@@ -375,7 +391,9 @@ g_keyfile_settings_backend_get_writable (GSettingsBackend *backend,
 {
   GKeyfileSettingsBackend *kfsb = G_KEYFILE_SETTINGS_BACKEND (backend);
 
-  return kfsb->writable && path_is_valid (kfsb, name);
+  return kfsb->writable &&
+         !g_hash_table_contains (kfsb->system_locks, name) &&
+         path_is_valid (kfsb, name);
 }
 
 static GPermission *
@@ -521,6 +539,8 @@ g_keyfile_settings_backend_finalize (GObject *object)
 
   g_key_file_free (kfsb->keyfile);
   g_object_unref (kfsb->permission);
+  g_key_file_free (kfsb->system_keyfile);
+  g_hash_table_unref (kfsb->system_locks);
 
   g_file_monitor_cancel (kfsb->file_monitor);
   g_object_unref (kfsb->file_monitor);
@@ -569,6 +589,61 @@ dir_changed (GFileMonitor       *monitor,
   g_keyfile_settings_backend_keyfile_writable (kfsb);
 }
 
+static void
+load_system_settings (GKeyfileSettingsBackend *kfsb)
+{
+  GError *error = NULL;
+  GKeyFile *keyfile;
+  // FIXME: just for test purposes, use two files present on Fedora
+  const char *db_path = "/etc/dconf/db/distro.d/20-authselect";
+  const char *lock_path = "/etc/dconf/db/distro.d/locks/20-authselect";
+  char *contents;
+  char **lines;
+  int i;
+
+  keyfile = g_key_file_new ();
+
+  if (!g_key_file_load_from_file (keyfile, db_path, G_KEY_FILE_NONE, &error))
+    {
+      if (!g_error_matches (error, G_FILE_ERROR, G_FILE_ERROR_NOENT))
+        g_warning ("Failed to read %s: %s", db_path, error->message);
+      g_clear_error (&error);
+      g_key_file_unref (keyfile);
+      kfsb->system_keyfile = g_key_file_new ();
+    }
+  else
+    {
+      g_debug ("Loaded system-wide settings from %s", db_path);
+      kfsb->system_keyfile = keyfile;
+    }
+
+  kfsb->system_locks = g_hash_table_new_full (g_str_hash, g_str_equal, g_free, NULL);
+
+  if (!g_file_get_contents (lock_path, &contents, NULL, &error))
+    {
+      if (!g_error_matches (error, G_FILE_ERROR, G_FILE_ERROR_NOENT))
+        g_warning ("Failed to read %s: %s", db_path, error->message);
+      g_clear_error (&error);
+      return;
+    }
+
+  lines = g_strsplit (contents, "\n", 0);
+  for (i = 0; lines[i]; i++)
+    {
+      const char *line = lines[i];
+      if (line[0] == '#')
+        continue;
+      if (line[0] == '\0')
+        continue;
+
+      g_debug ("Locking key %s", line);
+      g_hash_table_add (kfsb->system_locks, g_strdup (line));
+    }
+
+  g_strfreev (lines);
+  g_free (contents);
+}
+
 static void
 g_keyfile_settings_backend_constructed (GObject *object)
 {
@@ -602,6 +677,8 @@ g_keyfile_settings_backend_constructed (GObject *object)
 
   g_keyfile_settings_backend_keyfile_writable (kfsb);
   g_keyfile_settings_backend_keyfile_reload (kfsb);
+
+  load_system_settings (kfsb);
 }
 
 static void