Bug#436943: grub-pc: missing mapping from fs-block-no. to disk-block-no. in xfs.c

[Niels Boehm]

Package: grub-pc
Followup-For: Bug #436943


Okay, I hunted the problem down myself. It's a missing mapping from the file
system block numbering scheme ((agno << agbits) | block_in_ag) to the
on-partition block numbering (agno * agsize + block_in_ag) in the
grub_xfs_read_block() function.

It would affect all users who have a partition with more than one allocation
group with an agsize which is not a power of 2.
The problem arises when grub encounters files with blocks not on ag#0 and
directories which are extent lists not stored on ag#0.

I changed the offending file like that:

---- CUT HERE ----
--- grub2-1.96+20080512/fs/xfs.c	2008-02-02 15:15:31.000000000 +0100
+++ xfs.c_Niels	2008-06-28 12:40:39.487565975 +0200
@@ -162,4 +162,8 @@
   (grub_be_to_cpu64 (ino) >> GRUB_XFS_INO_AGBITS (data))
 
+#define GRUB_XFS_FSB_TO_BLOCK(data, fsb) \
+  (((fsb) >> (data)->sblock.log2_agblk) * (data)->agsize \
+ + ((fsb) & ((1 << (data)->sblock.log2_agblk) - 1)))
+
 #define GRUB_XFS_EXTENT_OFFSET(exts,ex) \
 	((grub_be_to_cpu32 (exts[ex][0]) & ~(1 << 31)) << 23 \
@@ -309,5 +313,5 @@
     grub_free (leaf);
 
-  return ret;
+  return GRUB_XFS_FSB_TO_BLOCK(node->data, ret);
 }
 
---- CUT HERE ----

The patch works fine for me, but I can't tell if I missed any intricacies,
since I'm not into grub development.

I reported it upstream, too.


Hope it helps,
Niels Böhm


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