=== modified file 'include/grub/file.h'
--- include/grub/file.h	2010-04-06 19:28:26 +0000
+++ include/grub/file.h	2010-03-21 23:45:49 +0000
@@ -39,6 +39,9 @@
   /* The file size.  */
   grub_off_t size;
 
+  /* If file is not easly seekable. Should be set by underlying layer.  */
+  int not_easly_seekable;
+
   /* Filesystem-specific data.  */
   void *data;
 
@@ -69,4 +72,10 @@
   return file->offset;
 }
 
+static inline int
+grub_file_seekable (const grub_file_t file)
+{
+  return !file->not_easly_seekable;
+}
+
 #endif /* ! GRUB_FILE_HEADER */

=== modified file 'io/gzio.c'
--- io/gzio.c	2010-04-06 19:28:26 +0000
+++ io/gzio.c	2010-03-31 20:45:40 +0000
@@ -173,6 +173,7 @@
     grub_uint8_t extra_flags;
     grub_uint8_t os_type;
   } hdr;
+
   grub_uint16_t extra_len;
   grub_uint32_t orig_len;
   grub_gzio_t gzio = file->data;
@@ -214,12 +215,14 @@
 
   grub_file_seek (gzio->file, grub_file_size (gzio->file) - 4);
 
-  if (grub_file_read (gzio->file, &orig_len, 4) != 4)
+  if (grub_file_seekable (gzio->file))
     {
-      grub_error (GRUB_ERR_BAD_FILE_TYPE, "unsupported gzip format");
-      return 0;
+      if (grub_file_read (gzio->file, &orig_len, 4) != 4)
+	{
+	  grub_error (GRUB_ERR_BAD_FILE_TYPE, "unsupported gzip format");
+	  return 0;
+	}
     }
-
   /* FIXME: this does not handle files whose original size is over 4GB.
      But how can we know the real original size?  */
   file->size = grub_le_to_cpu32 (orig_len);
@@ -1140,6 +1143,7 @@
   file->data = gzio;
   file->read_hook = 0;
   file->fs = &grub_gzio_fs;
+  file->not_easly_seekable = 1;
 
   if (!test_header (file))
     {
@@ -1241,7 +1245,6 @@
 
   return grub_errno;
 }
-
 
 
 static struct grub_fs grub_gzio_fs = {