=== modified file 'ChangeLog'
--- ChangeLog	2011-01-13 21:25:56 +0000
+++ ChangeLog	2011-01-14 23:53:37 +0000
@@ -1,3 +1,8 @@
+2011-01-15  Szymon Janc  <address@hidden>
+
+	* grub-core/kern/file.c (grub_file_read): Handle unknown file size.
+	(grub_file_seek): Likewise.
+
 2011-01-13  Vladimir Serbinenko  <address@hidden>
 
 	* grub-core/fs/zfs/zfsinfo.c (grub_cmd_zfs_bootfs): Quote bootpath and

=== modified file 'grub-core/kern/file.c'
--- grub-core/kern/file.c	2010-09-05 11:05:36 +0000
+++ grub-core/kern/file.c	2011-01-14 23:53:37 +0000
@@ -132,15 +132,18 @@ grub_file_read (grub_file_t file, void *
 {
   grub_ssize_t res;
 
-  if (file->offset > file->size)
+  if (file->size != GRUB_FILE_SIZE_UNKNOWN)
     {
-      grub_error (GRUB_ERR_OUT_OF_RANGE,
-		  "attempt to read past the end of file");
-      return -1;
-    }
+      if (file->offset > file->size)
+	{
+	  grub_error (GRUB_ERR_OUT_OF_RANGE,
+		      "attempt to read past the end of file");
+	  return -1;
+	}
 
-  if (len == 0 || len > file->size - file->offset)
-    len = file->size - file->offset;
+      if (len == 0 || len > file->size - file->offset)
+	len = file->size - file->offset;
+    }
 
   /* Prevent an overflow.  */
   if ((grub_ssize_t) len < 0)
@@ -171,16 +174,22 @@ grub_file_close (grub_file_t file)
 grub_off_t
 grub_file_seek (grub_file_t file, grub_off_t offset)
 {
-  grub_off_t old;
+  grub_off_t old = file->offset;
+
+  if (file->size == GRUB_FILE_SIZE_UNKNOWN && offset > file->offset)
+    {
+      if (grub_file_read (file, NULL, offset - file->offset) < 0)
+	return -1;
+      else
+	return old;
+    }
 
   if (offset > file->size)
     {
-      grub_error (GRUB_ERR_OUT_OF_RANGE,
-		  "attempt to seek outside of the file");
+      grub_error (GRUB_ERR_OUT_OF_RANGE, "attempt to seek outside of the file");
       return -1;
     }
 
-  old = file->offset;
   file->offset = offset;
   return old;
 }