Bug#503344: Grub-pc fails on IBM x3250 configured with RAID-1

[Bob Gilligan]

Package: grub-pc
Version: 1.96+20080724-10

After installing grub-pc on an IBM x3250 with two 160 GB drives, with 
the root filesystem configured using mdadm for RAID-1, grub fails to 
boot, printing:

Welcome to GRUB!

error: unknown device fd1
Entering rescue mode ...
grub rescue>

After troubleshooting, I found that the failure was occurring in 
grub_file_open() when grub_dl_load_file() was attempting to load the 
normal mode module.  The grub_file_open() function checks the return 
status of its call to grub_file_get_device_name() by checking the value 
of grub_errno.  If grub_errno is non-zero, grub_file_open() returns 
failure.  But grub_file_get_device_name() can succeed, but the error 
test fail, if grub_errno was set in some earlier operation.  In this 
case, apparently an early attempt to open a non-existent device set 
grub_errno.

The fix is to assign grub_errno before making the call to 
grub_file_get_device_name():

diff --git a/kern/file.c b/kern/file.c
index adf55da..5e605f9 100644
--- a/kern/file.c
+++ b/kern/file.c
@@ -59,6 +59,7 @@ grub_file_open (const char *name)
    char *device_name;
    char *file_name;

+  grub_errno = GRUB_ERR_NONE;  /* Used as error flag */
    device_name = grub_file_get_device_name (name);
    if (grub_errno)
      return 0;