1 files changed, 112 insertions, 0 deletions
diff --git a/grub-core/io/offset.c b/grub-core/io/offset.c
new file mode 100644
index 0000000..7e2db4a
--- /dev/null
+++ b/grub-core/io/offset.c
@@ -0,0 +1,112 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2013  Free Software Foundation, Inc.
+ *
+ *  GRUB is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  GRUB is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <grub/file.h>
+#include <grub/dl.h>
+
+GRUB_MOD_LICENSE ("GPLv3+");
+
+struct grub_offset_file
+{
+  grub_file_t parent;
+  grub_off_t off;
+};
+
+static grub_ssize_t
+grub_offset_read (grub_file_t file, char *buf, grub_size_t len)
+{
+  struct grub_offset_file *data = file->data;
+  if (grub_file_seek (data->parent, data->off + file->offset) == (grub_off_t) -1)
+    return -1;
+  return grub_file_read (data->parent, buf, len);
+}
+
+static grub_err_t
+grub_offset_close (grub_file_t file)
+{
+  struct grub_offset_file *data = file->data;
+
+  if (data->parent)
+    grub_file_close (data->parent);
+
+  /* No need to close the same device twice.  */
+  file->device = 0;
+
+  return 0;
+}
+
+static struct grub_fs grub_offset_fs = {
+  .name = "offset",
+  .fs_dir = 0,
+  .fs_open = 0,
+  .fs_read = grub_offset_read,
+  .fs_close = grub_offset_close,
+  .fs_label = 0,
+  .next = 0
+};
+
+void
+grub_file_offset_close (grub_file_t file)
+{
+  struct grub_offset_file *off_data = file->data;
+  off_data->parent = NULL;
+  grub_file_close (file);
+}
+
+grub_file_t
+grub_file_offset_open (grub_file_t parent, enum grub_file_type type,
+		       grub_off_t start, grub_off_t size)
+{
+  struct grub_offset_file *off_data;
+  grub_file_t off_file, last_off_file;
+  grub_file_filter_id_t filter;
+
+  off_file = grub_zalloc (sizeof (*off_file));
+  off_data = grub_zalloc (sizeof (*off_data));
+  if (!off_file || !off_data)
+    {
+      grub_free (off_file);
+      grub_free (off_data);
+      return 0;
+    }
+
+  off_data->off = start;
+  off_data->parent = parent;
+
+  off_file->device = parent->device;
+  off_file->data = off_data;
+  off_file->fs = &grub_offset_fs;
+  off_file->size = size;
+
+  last_off_file = NULL;
+  for (filter = GRUB_FILE_FILTER_COMPRESSION_FIRST;
+       off_file && filter <= GRUB_FILE_FILTER_COMPRESSION_LAST; filter++)
+    if (grub_file_filters[filter])
+      {
+	last_off_file = off_file;
+	off_file = grub_file_filters[filter] (off_file, type);
+      }
+
+  if (!off_file)
+    {
+      off_data->parent = NULL;
+      grub_file_close (last_off_file);
+      return 0;
+    }
+  return off_file;
+}