[PATCH] fix UFS superblock alignment issues

[PATCH] fix UFS superblock alignment issues

[Eric Sandeen]

ufs2 fails to mount on x86_64, claiming bad magic.  This is because 
ufs_super_block_third's fs_un1 member is padded out by 4 bytes for
8-byte alignment, pushing down the rest of the struct.

Forcing this to be packed solves it.  I took a quick look over
other on-disk structures and didn't immediately find other problems.
I was able to mount & ls a populated ufs2 filesystem w/ this change.

Thanks,
-Eric

Signed-off-by: Eric Sandeen <sandeen@redhat.com>

Index: linux-2.6.18/include/linux/ufs_fs.h
===================================================================
--- linux-2.6.18.orig/include/linux/ufs_fs.h
+++ linux-2.6.18/include/linux/ufs_fs.h
@@ -900,7 +900,7 @@ struct ufs_super_block_third {
 			__fs64   fs_csaddr;	/* blk addr of cyl grp summary area */
 			__fs64    fs_pendingblocks;/* blocks in process of being freed */
 			__fs32    fs_pendinginodes;/*inodes in process of being freed */
-		} fs_u2;
+		} __attribute__ ((packed)) fs_u2;
 	} fs_un1;
 	union {
 		struct {

Re: [PATCH] fix UFS superblock alignment issues

[Eric Sandeen]

Eric Sandeen wrote:
> ufs2 fails to mount on x86_64, claiming bad magic.  This is because 
> ufs_super_block_third's fs_un1 member is padded out by 4 bytes for
> 8-byte alignment, pushing down the rest of the struct.
> 
> Forcing this to be packed solves it.  I took a quick look over
> other on-disk structures and didn't immediately find other problems.
> I was able to mount & ls a populated ufs2 filesystem w/ this change.

I should also mention that this seems to be a regression from
2.6.17->2.6.18, so perhaps it's a candidate for 2.6.18.x updates.

Thanks,

-Eric

Re: [PATCH] fix UFS superblock alignment issues

[Randy Dunlap]

On Tue, 31 Oct 2006 09:22:30 -0600 Eric Sandeen wrote:

> Eric Sandeen wrote:
> > ufs2 fails to mount on x86_64, claiming bad magic.  This is because 
> > ufs_super_block_third's fs_un1 member is padded out by 4 bytes for
> > 8-byte alignment, pushing down the rest of the struct.
> > 
> > Forcing this to be packed solves it.  I took a quick look over
> > other on-disk structures and didn't immediately find other problems.
> > I was able to mount & ls a populated ufs2 filesystem w/ this change.
> 
> I should also mention that this seems to be a regression from
> 2.6.17->2.6.18, so perhaps it's a candidate for 2.6.18.x updates.

Please send it to stable@kernel.org .

---
~Randy