linux-kernel - Re: NILFS2: double uuid

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Message-ID: <5576E44F.5030201@lab.ntt.co.jp>
Date:	Tue, 09 Jun 2015 22:04:15 +0900
From:	Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>
To:	Karel Zak <kzak@...hat.com>
CC:	Heinz Diehl <htd+ml@...tha.org>, linux-kernel@...r.kernel.org,
	linux-nilfs@...r.kernel.org
Subject: Re: NILFS2: double uuid

Hi,

On 2015/06/09 17:53, Karel Zak wrote:
> On Tue, Jun 09, 2015 at 12:31:27AM +0900, Ryusuke Konishi wrote:
>> It looks like the backup super block should be dropped from candidates
>> if its device size (sbp->s_dev_size) doesn't match the partition size.
>
> Yeah, fixed:
> http://git.kernel.org/cgit/utils/util-linux/util-linux.git/commit/?id=00817742ce360119e079a33e12cf84118ff7c63e
>
> Note that workaround is to not use nilfs2 on the last partition or
> have a tiny gap (1 sector is enough) between last partition and the
> end of the whole-disk.
>
>      Karel
>

Thanks for your quick work!

I tested the patch.  It almost worked fine.
One issue I found is a transient state after fs-resizing.

After shrinking the file system, both superblocks dropped and
lsblk failed to detect the filesystem:

$ sudo LD_LIBRARY_PATH=/usr/local/lib lsblk -f
NAME   FSTYPE  LABEL           UUID 
MOUNTPOINT
[...]
sdb
`-sdb1 nilfs2                  2d7cd130-82a0-4a3c-b8a8-4ac5a26f5703 /test

$ sudo nilfs-resize -y /dev/sdb1 1G
Partition size = 2146435072 bytes.
Shrink the filesystem size from 2146435072 bytes to 1073741824 bytes.
128 segments will be truncated from segnum 127.
Moving 103 in-use segments.
progress |***********************************************|
Done.

$ sudo umount /test
$ sudo mount /dev/sdb1 /test
$ sudo LD_LIBRARY_PATH=/usr/local/lib lsblk -f
NAME   FSTYPE  LABEL           UUID 
MOUNTPOINT
[...]
sdb
`-sdb1                                                              /test

This blank state continued until I shrank the partition or
re-extended the filesystem to the partition size.

Could you consider confining the s_dev_size test only to the
backup superblock ?

It seems that we don't have to drop the primary super block
even if s_dev_size doesn't fit to the partition size.


Regards,
Ryusuke Konishi

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