Re: [PATCH 0/20] return f_fsid for statfs(2)

[Coly Li <coly.li@suse.de>]

Andreas Dilger Wrote:
> On Jan 20, 2009  12:30 +0800, Coly Li wrote:
>> Ext[234] is sophisticated to have on-disk uuid record. Most file systems
>> in the patches (except jfs and reiser3) do not have a persistent uuid,
>> a reasonable/feasible solution without media format modification is fsid
>> in boot/mount life cycle. That's why huge_encode_dev(sb->s_bdev->bd_dev)
>> is used here.  For jfs and reiserfs3, is there any use case for
>> persistent fsid cross boots ?
> 
> I would say yes, this is worthwhile to do, or the fsid can change between
> boots unnecessarily.
> 
If no partitioning happens between boots/mounts, fsid from huge_encode_dev() should be identical.
For non-uuid file systems, IMHO huge_encode_dev() method is acceptable.
But YES, for jfs and reiserfs3 there is chance to provide persistent fsid cross boots, here are
examples,
- in fs/jfs/super.c:jfs_statfs(), generate f_fsid by:
	buf->f_fsid.val[0] = crc32_le(0, sbi->uuid, sizeof(sbi->uuid)/2);
	buf->f_fsid.val[1] = crc32_le(0, sbi->uuid + sizeof(sbi->uuid)/2,
					sizeof(sbi->uuid)/2);
- in fs/reiserfs/super.c:reiserfs_statfs(), generate f_fsid by:
	buf->f_fsid.val[0] = (u32)crc32_le(0, rs->s_uuid, sizeof(rs->s_uuid)/2);
	buf->f_fsid.val[1] = (u32)crc32_le(0, rs->s_uuid + sizeof(rs->s_uuid)/2,
				sizeof(rs->s_uuid)/2);

I will update corresponded patches for the implementation. Thanks for your comments.

-- 
Coly Li
SuSE Labs