[gvfs] metadata: don't crash if tree write out failed

[Ondrej Holy <oholy src gnome org>]

commit f7f18bb6e7576672c2240c8ead8dfa4a2668d478
Author: Ondrej Holy <oholy redhat com>
Date:   Tue Mar 10 12:54:39 2015 +0100

    metadata: don't crash if tree write out failed
    
    meta_tree_init can fail after we failed to write out an updated tree.
    Backup corrupted file and start with empty tree to avoid consequent
    crashes.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=598561

 metadata/metatree.c |   46 +++++++++++++++++++++++++++++++++++++++++++---
 1 files changed, 43 insertions(+), 3 deletions(-)
---
diff --git a/metadata/metatree.c b/metadata/metatree.c
index 4c6d5f0..4964c68 100644
--- a/metadata/metatree.c
+++ b/metadata/metatree.c
@@ -643,6 +643,7 @@ meta_tree_refresh_locked (MetaTree *tree, gboolean force_reread)
   return TRUE;
 }
 
+/* NB: The tree is uninitialized if FALSE is returned! */
 gboolean
 meta_tree_refresh (MetaTree *tree)
 {
@@ -2339,7 +2340,16 @@ meta_tree_flush_locked (MetaTree *tree)
 
   builder = meta_builder_new ();
 
-  copy_tree_to_builder (tree, tree->root, builder->root);
+  if (tree->root)
+    {
+      copy_tree_to_builder (tree, tree->root, builder->root);
+    }
+  else
+    {
+      /* It shouldn't happen, because tree is recovered in case of failed write
+       * out. Skip copy_tree_to_builder to avoid crash. */
+      g_warning ("meta_tree_flush_locked: tree->root == NULL, possible data loss");
+    }
 
   if (tree->journal)
     apply_journal_to_builder (tree, builder);
@@ -2347,14 +2357,44 @@ meta_tree_flush_locked (MetaTree *tree)
   res = meta_builder_write (builder,
                            meta_tree_get_filename (tree));
   if (res)
-    /* Force re-read since we wrote a new file */
-    res = meta_tree_refresh_locked (tree, TRUE);
+    {
+      /* Force re-read since we wrote a new file */
+      res = meta_tree_refresh_locked (tree, TRUE);
+
+      if (tree->root == NULL)
+       {
+         /* It shouldn't happen. We failed to write out an updated tree
+          * probably, therefore all the data are lost. Backup the file and
+          * reload the tree to avoid further crashes. */
+         GTimeVal tv;
+         char *timestamp, *backup;
+
+         g_get_current_time (&tv);
+         timestamp = g_time_val_to_iso8601 (&tv);
+         backup = g_strconcat (meta_tree_get_filename (tree), ".backup.",
+                               timestamp, NULL);
+         g_rename (meta_tree_get_filename (tree), backup);
+
+         g_warning ("meta_tree_flush_locked: tree->root == NULL, possible data loss\n"
+                    "corrupted file was moved to: %s\n"
+                    "(please make a comment on https://bugzilla.gnome.org/show_bug.cgi?id=598561 "
+                    "and attach the corrupted file)",
+                    backup);
+
+         g_free (timestamp);
+         g_free (backup);
+
+         res = meta_tree_refresh_locked (tree, TRUE);
+         g_assert (res);
+       }
+  }
 
   meta_builder_free (builder);
 
   return res;
 }
 
+/* NB: The tree can be uninitialized if FALSE is returned! */
 gboolean
 meta_tree_flush (MetaTree *tree)
 {