Re: [PATCH 0/8] Introduce offline fsid/chunk tree uuid change for btrfstune.

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

-------- Original Message  --------
Subject: Re: [PATCH 0/8] Introduce offline fsid/chunk tree uuid change 
for btrfstune.
From: David Sterba <dsterba@suse.cz>
To: Qu Wenruo <quwenruo@cn.fujitsu.com>
Date: 2015年05月05日 23:20

> On Tue, May 05, 2015 at 02:16:38PM +0800, Qu Wenruo wrote:
>> This patchset will introduce offline fsid/chunk tree uuid change
>> function to btrfstune command, with "-u" and "-U" options respectively.
>>
>> The implement is in-place btrfs_header modification, without transaction
>> protection. So the uuid change can be done on any valid image even it is
>> already full.
>>
>> Since we don't use transaction to protect the convert, it's possible one
>> can stop the running convert progress, causing the fs in a inconsistent
>> status and unable to be mounted.
>> To avoid such problem, we introduce new open ctree flags
>> OPEN_CTREE_IGNORE_FSID, allowing btrfstune to finish the convert.
>
> Code looks good to me. I'm not sure whether it should land in btrfstune
> or in 'btrfs' proper.
>
> * btrfstune should go away at some point, so I'd rather not add new
>    features there
>
> * 'btrfs property set -t filesystem uuid' seems best to me at this moment
Good idea.

I'll change it to property in next version.
>
> A minor suggestion: set BTRFS_SUPER_FLAG_ERROR on the filesystem during
> the conversion and drop it after it finishes successfully. It's merely a
> hint that there's something wrong with the filesytem, the mount will
> fail because filesystem uuid would not match the device id.
>
Nice idea too.
But I'd like to use more specific flags like
BTRFS_SUPER_FLAG_UUID_CHANGING to give better info if kernel can't mount it.

Thanks for all these advice!
Qu