GFile: Clean up file_copy_fallback to fix SEGV with btrfs

Ok, this function was just an awful mess before.  Now the problem
domain is not trivial, and I won't claim this new code is *beautiful*,
but it should fix the bug at hand, and be somewhat less prone to
failure for the next person who tries to modify it.  There's only one
unref call for each object now.

https://bugzilla.gnome.org/show_bug.cgi?id=692408

gio/gfile.c

@@ -2982,11 +2982,11 @@ file_copy_fallback (GFile                  *source,
                     gpointer                progress_callback_data,
                     GError                **error)
 {
-  GInputStream *in;
+  gboolean ret = FALSE;
-  GOutputStream *out;
+  GInputStream *in = NULL;
-  GFileInfo *info;
+  GOutputStream *out = NULL;
+  GFileInfo *info = NULL;
   const char *target;
-  gboolean result;
 
   /* need to know the file type */
   info = g_file_query_info (source,
@@ -2994,9 +2994,8 @@ file_copy_fallback (GFile                  *source,
                             G_FILE_QUERY_INFO_NOFOLLOW_SYMLINKS,
                             cancellable,
                             error);
-
+  if (!info)
-  if (info == NULL)
+    goto out;
-          return FALSE;
 
   /* Maybe copy the symlink? */
   if ((flags & G_FILE_COPY_NOFOLLOW_SYMLINKS) &&
@@ -3006,16 +3005,12 @@ file_copy_fallback (GFile                  *source,
       if (target)
         {
           if (!copy_symlink (destination, flags, cancellable, target, error))
-            {
+            goto out;
-              g_object_unref (info);
-              return FALSE;
-            }
 
-          g_object_unref (info);
+          ret = TRUE;
-          goto copied_file;
+          goto out;
         }
         /* ... else fall back on a regular file copy */
-        g_object_unref (info);
     }
   /* Handle "special" files (pipes, device nodes, ...)? */
   else if (g_file_info_get_file_type (info) == G_FILE_TYPE_SPECIAL)
@@ -3023,16 +3018,14 @@ file_copy_fallback (GFile                  *source,
       /* FIXME: could try to recreate device nodes and others? */
       g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED,
                            _("Can't copy special file"));
-      g_object_unref (info);
+      goto out;
-      return FALSE;
     }
+
   /* Everything else should just fall back on a regular copy. */
-  else
-    g_object_unref (info);
 
   in = open_source_for_copy (source, destination, flags, cancellable, error);
-  if (in == NULL)
+  if (!in)
-    return FALSE;
+    goto out;
 
   if (flags & G_FILE_COPY_OVERWRITE)
     {
@@ -3047,29 +3040,33 @@ file_copy_fallback (GFile                  *source,
       out = (GOutputStream *)g_file_create (destination, 0, cancellable, error);
     }
 
-  if (out == NULL)
+  if (!out)
-    {
+    goto out;
-      g_object_unref (in);
-      return FALSE;
-    }
 
 #ifdef HAVE_SYS_IOCTL_H
   if (G_IS_FILE_DESCRIPTOR_BASED (in) && G_IS_FILE_DESCRIPTOR_BASED (out))
     {
       GError *reflink_err = NULL;
 
-      result = btrfs_reflink_with_progress (in, out, info, cancellable,
+      if (!btrfs_reflink_with_progress (in, out, info, cancellable,
-                                            progress_callback, progress_callback_data,
+                                        progress_callback, progress_callback_data,
-                                            &reflink_err);
+                                        &reflink_err))
-
-      if (result || !g_error_matches (reflink_err, G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED))
         {
-          if (!result)
+          if (g_error_matches (reflink_err, G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED))
-            g_propagate_error (error, reflink_err);
+            {
-          goto cleanup;
+              g_clear_error (&reflink_err);
+            }
+          else
+            {
+              g_propagate_error (error, reflink_err);
+              goto out;
+            }
         }
       else
-        g_clear_error (&reflink_err);
+        {
+          ret = TRUE;
+          goto out;
+        }
     }
 #endif
 
@@ -3078,45 +3075,60 @@ file_copy_fallback (GFile                  *source,
     {
       GError *splice_err = NULL;
 
-      result = splice_stream_with_progress (in, out, cancellable,
+      if (!splice_stream_with_progress (in, out, cancellable,
-                                            progress_callback, progress_callback_data,
+                                        progress_callback, progress_callback_data,
-                                            &splice_err);
+                                        &splice_err))
-
-      if (result || !g_error_matches (splice_err, G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED))
         {
-          if (!result)
+          if (g_error_matches (splice_err, G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED))
-            g_propagate_error (error, splice_err);
+            {
-          goto cleanup;
+              g_clear_error (&splice_err);
+            }
+          else
+            {
+              g_propagate_error (error, splice_err);
+              goto out;
+            }
         }
       else
-        g_clear_error (&splice_err);
+        {
+          ret = TRUE;
+          goto out;
+        }
     }
 
 #endif
-  result = copy_stream_with_progress (in, out, source, cancellable,
+  
-                                      progress_callback, progress_callback_data,
+  /* A plain read/write loop */
-                                      error);
+  if (!copy_stream_with_progress (in, out, source, cancellable,
+                                  progress_callback, progress_callback_data,
+                                  error))
+    goto out;
 
-cleanup:
+  ret = TRUE;
-  /* Don't care about errors in source here */
+ out:
-  g_input_stream_close (in, cancellable, NULL);
-
-  /* But write errors on close are bad! */
-  if (!g_output_stream_close (out, cancellable, result ? error : NULL))
-    result = FALSE;
-
-  g_object_unref (in);
-  g_object_unref (out);
-
-  if (result == FALSE)
-    return FALSE;
-
-copied_file:
   /* Ignore errors here. Failure to copy metadata is not a hard error */
-  g_file_copy_attributes (source, destination,
+  if (ret)
-                          flags, cancellable, NULL);
+    (void) g_file_copy_attributes (source, destination,
+                                   flags, cancellable, NULL);
 
-  return TRUE;
+  if (in)
+    {
+      /* Don't care about errors in source here */
+      (void) g_input_stream_close (in, cancellable, NULL);
+      g_object_unref (in);
+    }
+
+  if (out)
+    {
+      /* But write errors on close are bad! */
+      if (!g_output_stream_close (out, cancellable, ret ? error : NULL))
+        ret = FALSE;
+      g_object_unref (out);
+    }
+  
+  g_clear_object (&info);
+
+  return ret;
 }
 
 /**