From: Andrei Borzenkov <arvidjaar@gmail.com>
To: thomas <thomas85@mail.ch>, linux-btrfs@vger.kernel.org
Subject: Re: btrfs send subvolume from read-only mount with missing ro=true flag?
Date: Sat, 16 Dec 2023 19:45:26 +0300 [thread overview]
Message-ID: <a5699aee-0e36-4c4c-96b3-aaa04e6b74ea@gmail.com> (raw)
In-Reply-To: <a41a77e3-95aa-450f-9712-c5681f8a8912@mail.ch>
On 16.12.2023 17:47, thomas wrote:
> I have a btrfs volume damaged (it seems beyond repair..) by writing to
> it via an unstable USB connection which disconnected at a particularly
> bad time it seems.
>
> I found I can still mount said volume in read-only mount using:
>
> |mount -t btrfs -o ro,rescue=ignorebadroots,rescue=ignoredatacsums
> /dev/ice /mnt/point |
>
> Now I would have liked to copy some of the subvolumes from that damaged
> volume over to a new one, but sadly |`btrfs send||`| disallows using
> subvolumes that don't already have a ro=true flag on them, so only
> read-only snapshots are allowed as source.
>
> Can I somehow make |`btrfs send||`| believe that on a read-only mount
> everything is guaranteed to be read-only, even if the subvolume does not
> have that read-only flag? Sadly because I can only mount said damaged
> btrfs volume in read-only mode I can't add the read-only flag to the
> subvolumes I'd like to copy..
>
>
Theoretically even if filesystem is mounted ro, it is possible to
remount it rw on the fly. So one would need to add some mutual exclusion
between "btrfs send" and "mount -o remount,rw". Not sure how difficult
it is or whether it is worth the troubles.
What is the exact reason to use "btrfs send" in this case? Why cannot
you simply archive the content and extract on new filesystem?
next prev parent reply other threads:[~2023-12-16 16:45 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-16 14:47 btrfs send subvolume from read-only mount with missing ro=true flag? thomas
2023-12-16 16:45 ` Andrei Borzenkov [this message]
2023-12-16 22:55 ` thomas
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