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grub 2: xfs.mod reads some directories incorrectly

From: bitbucket
Subject: grub 2: xfs.mod reads some directories incorrectly
Date: Sun, 29 Jun 2008 20:00:47 +0200


I want to bring to your attention a problem with the XFS module of grub2 since 
I was told that you might not always pay attention to the bugtracker. I've 
reported the bug at as well as on the Debian BTS, so I'm 
pasting the interesting snippets from the latter one for your convenience:

From: Alex Malinovich <address@hidden>
To: address@hidden
Subject: Re: Bug#436943: another confirmation
Date: Tue, 12 Feb 2008 05:06:15 -0800

[Message part 1 (text/plain, inline)]

On Tue, 2008-02-12 at 13:19 +0100, Robert Millan wrote:
> On Tue, Feb 12, 2008 at 02:14:55AM -0800, Alex Malinovich wrote:
> > 
> > Oddly, trying to do "ls (hd0,1)/" works just fine. Yet when running
> "ls
> > (hd0,1)/boot" gives that same "out of partition error", even
> > though /boot is NOT on a separate partition.
> Alex, what is your filesystem in (hd0,1)/ ?
> Can you identify the problem if you do:
>   set debug=all
>   ls (hd0,1)/boot

The fs on hd0,1 is xfs. I just did an fsck on it and the fs itself is

Since it's hard to paste a good amount of code that happens at boot,
here's what I get when running grub-emu from the console with the above
commands. I'll do a reboot later and verify that I get the same errors.
If I see anything different on a regular boot I'll send in a follow-up

One thing that might be potentially useful, when just doing the ls
without the debug=all, I actually get a little bit of output prior to
the out of partition error. In this particular case the output is:

grub> ls (hd0,1)/boot
?^^ ?^^ ^Q^_                                                                   
           error: out of partition

Not sure what those extra characters are about, but they are consistent
across multiple runs of grub-emu.

So, running ls after setting debug=all I get:

grub> ls (hd0,1)/boot
 /home/rmh/hacking/grub/svn/upload/grub2-1.96+20080210/kern/disk.c:371: Read 
 of range: sector 0xffffffffef400000 (out of partition).
 /home/rmh/hacking/grub/svn/upload/grub2-1.96+20080210/kern/disk.c:364: of 
range: sector 0xffffffffef400000 (out of partition).

repeating a few hundred times. There's some other scattered output but
it's very hard to make out. I do see some lines about detecting and
opening the xfs filesystem early in the log.

From: Niels Boehm <address@hidden>
To: Debian Bug Tracking System <address@hidden>
Subject: grub-pc: xfs.mod reads some directories incorrectly
Date: Sat, 28 Jun 2008 08:15:33 +0200

Package: grub-pc
Version: 1.96+20080512-1
Followup-For: Bug #436943


grub2 fails for me in the aforementioned manner. It is unable to read
anything from /boot or /boot/grub which are both on my root partition with
an xfs file system.

Trying to ls some directories, I find that some read without problem
(apparently ones containing only a few entries, like / /mnt /media /lib64
for example) and others produce garbled output and the "out of partition"
error (ones with many entries, like /boot /boot/grub /etc /bin for example).

I checked the root fs with /usr/sbin/xfs_check, but it looks alright.

And if I remember correctly, I created the root fs not long ago, so it
should have quite recent data structures. The log being version 2 confirms

# xfs_info /
meta-data=/dev/root              isize=256    agcount=4, agsize=64510 blks
         =                       sectsz=512   attr=2
data     =                       bsize=4096   blocks=258040, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096
log      =internal               bsize=4096   blocks=1200, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=0
realtime =none                   extsz=4096   blocks=0, rtextents=0

From: Niels Boehm <address@hidden>
To: Debian Bug Tracking System <address@hidden>
Subject: grub-pc: missing mapping from fs-block-no. to disk-block-no. in xfs.c
Date: Sat, 28 Jun 2008 14:50:36 +0200

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.

From: address@hidden
To: Robert Millan <address@hidden>
Cc: address@hidden
Subject: Re: Bug#436943: grub-pc: xfs.mod reads some directories incorrectly
Date: Sun, 29 Jun 2008 18:36:08 +0200

On Sunday 29 June 2008, Robert Millan wrote:
> The version you're using (1.96+20080512-1) is a bit old.  Could you check
> if this problem is reproducible with the sid one?  Or, since I notice you
> sent this upstream (thanks!), with latest CVS.

It the same with 1.96+20080626-1. And I also had a look at the source of the 
CVS version and it looks like the mapping is still missing there (tho it's a 
bit strange that they didn't notice it when they added uuid detection to 
xfs.c - maybe they happen to have agsizes that are a power of 2), but I'm not 
sure. I'd prefer to stick to the normal packages, since I don't really feel 
at home with package maintenance stuff.

Niels Böhm

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