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From:   Graham Cobb <g.btrfs@cobb.uk.net>
To:     dsterba@suse.cz, Martin Raiber <martin@urbackup.org>,
        Nikolay Borisov <nborisov@suse.com>,
        linux-btrfs@vger.kernel.org
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 <20210908183312.GU3379@twin.jikos.cz>
Subject: Re: [PATCH v2] btrfs: Remove received information from snapshot on
 ro->rw switch
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Date:   Wed, 8 Sep 2021 22:24:14 +0100
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On 08/09/2021 19:33, David Sterba wrote:
> On Wed, Sep 08, 2021 at 04:34:47PM +0000, Martin Raiber wrote:

<snip>

>> For example I had the problem of partial subvols after a sudden
>> restart during receive. No problem, just receive to a directory that
>> gets deleted on startup then move the subvol to the final location
>> after completion. To move the subvol it needs to be temporarily set rw
>> for some reason. I'm sure there is some better solution but patterns
>> like this might be out there.
> 
> Thanks, that's a case we should take into account. And there are
> probably more, but I'm not using send/receive much so that's another
> reason why I've been hesitant to merge the patch due to lack of
> understanding of the use case.
> 

This seems to be an important change to make, but is user-affecting. A
few ideas:

1) Can it be made optional? On by default but possible to turn off
(mount option, sys file, ...) if you really need to retain the current
behaviour.

2) Is there a way to engage with the developers and user community for
popular tools which make heavy use of snapshotting and/or send/receive
for discussion and testing? For example, btrbk, snapper, distros.

3) How about adding an IOCTL to allow the user to set/delete the
received_uuid? Only intended for cases which really need to emulate the
removed behaviour. This could be a less complex long term solution than
keeping option 1 indefinitely.

Graham