Re: [PATCH][RFC] btrfs: introduce rescue=onlyfs

[Lukas Straub <lukasstraub2@web.de>]

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On Wed,  1 Jul 2020 10:44:38 -0400
Josef Bacik <josef@toxicpanda.com> wrote:

> One of the things that came up consistently in talking with Fedora about
> switching to btrfs as default is that btrfs is particularly vulnerable
> to metadata corruption.  If any of the core global roots are corrupted,
> the fs is unmountable and fsck can't usually do anything for you without
> some special options.
> 
> Qu addressed this sort of with rescue=skipbg, but that's poorly named as
> what it really does is just allow you to operate without an extent root.
> However there are a lot of other roots, and I'd rather not have to do
> 
> mount -o rescue=skipbg,rescue=nocsum,rescue=nofreespacetree,rescue=blah
> 
> Instead take his original idea and modify it so it just works for
> everything.  Turn it into rescue=onlyfs, and then any major root we fail
> to read just gets left empty and we carry on.
> 
> Obviously if the fs roots are screwed then the user is in trouble, but
> otherwise this makes it much easier to pull stuff off the disk without
> needing our special rescue tools.  I tested this with my TEST_DEV that
> had a bunch of data on it by corrupting the csum tree and then reading
> files off the disk.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> ---
> 
> I'm not married to the rescue=onlyfs name, if we can think of something better
> I'm good.

Maybe you could go a step further and automatically switch to rescue mode if something is corrupt. This is easier for the user than having to remember the mount flags.

Regards,
Lukas Straub

> Also rescue=skipbg is currently only sitting in misc-next, which is why I'm
> killing it with this patch, we haven't sent it upstream so we're good to change
> it now before it lands.
> 
>  fs/btrfs/block-group.c |  2 +-
>  fs/btrfs/ctree.h       |  2 +-
>  fs/btrfs/disk-io.c     | 76 ++++++++++++++++++++++--------------------
>  fs/btrfs/inode.c       |  6 +++-
>  fs/btrfs/super.c       | 27 +++++++--------
>  fs/btrfs/volumes.c     |  4 +--
>  6 files changed, 63 insertions(+), 54 deletions(-)
> ...

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