Fix trashing on overlayfs

In order to determine whether to trash a file to the home directory, we
compare its st_dev to our home directory's st_dev field.

This is the wrong thing to do on overlayfs when deleting files, because
st_dev contains the ID of the filesystem providing the file (which can
be the lower or upper filesystem), but directories always return the ID
of the overlayfs. Thus the comparison fails and we are unable to trash
the file.

Fix this by checking st_dev of the parent directory when we are deleting
a file.

Also adjust `test_trash_not_supported` for this - make its st_dev check
look at the parent directory's `st_dev` rather than the temporary file's
own.

Fixes #1027.

gio/glocalfile.c

@@ -1893,6 +1893,7 @@ g_local_file_trash (GFile         *file,
   char *original_name, *original_name_escaped;
   int i;
   char *data;
+  char *path;
   gboolean is_homedir_trash;
   char *delete_time = NULL;
   int fd;
@@ -1917,6 +1918,24 @@ g_local_file_trash (GFile         *file,
 
   is_homedir_trash = FALSE;
   trashdir = NULL;
+
+  /* On overlayfs, a file's st_dev will be different to the home directory's.
+   * We still want to create our trash directory under the home directory, so
+   * instead we should stat the directory that the file we're deleting is in as
+   * this will have the same st_dev.
+   */
+  if (!S_ISDIR (file_stat.st_mode))
+    {
+      path = g_path_get_dirname (local->filename);
+      /* If the parent is a symlink to a different device then it might have
+       * st_dev equal to the home directory's, in which case we will end up
+       * trying to rename across a filesystem boundary, which doesn't work. So
+       * we use g_stat here instead of g_lstat, to know where the symlink
+       * points to. */
+      g_stat (path, &file_stat);
+      g_free (path);
+    }
+
   if (file_stat.st_dev == home_stat.st_dev)
     {
       is_homedir_trash = TRUE;

gio/tests/trash.c

@@ -35,23 +35,26 @@ test_trash_not_supported (void)
   GFileInfo *info;
   GError *error = NULL;
   gboolean ret;
-  GStatBuf file_stat, home_stat;
+  gchar *parent_dirname;
+  GStatBuf parent_stat, home_stat;
 
   /* The test assumes that tmp file is located on system internal mount. */
   file = g_file_new_tmp ("test-trashXXXXXX", &stream, &error);
+  parent_dirname = g_path_get_dirname (g_file_peek_path (file));
   g_assert_no_error (error);
-  g_assert_cmpint (g_lstat (g_file_peek_path (file), &file_stat), ==, 0);
+  g_assert_cmpint (g_stat (parent_dirname, &parent_stat), ==, 0);
-  g_test_message ("File: %s (dev: %" G_GUINT64_FORMAT ")",
+  g_test_message ("File: %s (parent st_dev: %" G_GUINT64_FORMAT ")",
-                  g_file_peek_path (file), (guint64) file_stat.st_dev);
+                  g_file_peek_path (file), (guint64) parent_stat.st_dev);
 
   g_assert_cmpint (g_stat (g_get_home_dir (), &home_stat), ==, 0);
-  g_test_message ("Home: %s (dev: %" G_GUINT64_FORMAT ")",
+  g_test_message ("Home: %s (st_dev: %" G_GUINT64_FORMAT ")",
                   g_get_home_dir (), (guint64) home_stat.st_dev);
 
-  if (file_stat.st_dev == home_stat.st_dev)
+  if (parent_stat.st_dev == home_stat.st_dev)
     {
       g_test_skip ("The file has to be on another filesystem than the home trash to run this test");
 
+      g_free (parent_dirname);
       g_object_unref (stream);
       g_object_unref (file);
 
@@ -85,6 +88,7 @@ test_trash_not_supported (void)
   g_io_stream_close (G_IO_STREAM (stream), NULL, &error);
   g_assert_no_error (error);
 
+  g_free (parent_dirname);
   g_object_unref (info);
   g_object_unref (stream);
   g_object_unref (file);