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From:   Florian Weimer <fweimer@redhat.com>
To:     Jeff Layton <jlayton@kernel.org>
Cc:     "J. Bruce Fields" <bfields@fieldses.org>,
        Theodore Ts'o <tytso@mit.edu>, Jan Kara <jack@suse.cz>,
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Subject: Re: [man-pages RFC PATCH v4] statx, inode: document the new
 STATX_INO_VERSION field
References: <166259786233.30452.5417306132987966849@noble.neil.brown.name>
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        <20220908182252.GA18939@fieldses.org>
        <44efe219dbf511492b21a653905448d43d0f3363.camel@kernel.org>
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        <125df688dbebaf06478b0911e76e228e910b04b3.camel@kernel.org>
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Date:   Mon, 12 Sep 2022 15:20:46 +0200
In-Reply-To: <7c71050e139a479e08ab7cf95e9e47da19a30687.camel@kernel.org> (Jeff
        Layton's message of "Mon, 12 Sep 2022 08:55:04 -0400")
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* Jeff Layton:

> On Mon, 2022-09-12 at 14:13 +0200, Florian Weimer wrote:
>> * Jeff Layton:
>>=20
>> > To do this we'd need 2 64-bit fields in the on-disk and in-memory=20
>> > superblocks for ext4, xfs and btrfs. On the first mount after a crash,
>> > the filesystem would need to bump s_version_max by the significant
>> > increment (2^40 bits or whatever). On a "clean" mount, it wouldn't need
>> > to do that.
>> >=20
>> > Would there be a way to ensure that the new s_version_max value has ma=
de
>> > it to disk? Bumping it by a large value and hoping for the best might =
be
>> > ok for most cases, but there are always outliers, so it might be
>> > worthwhile to make an i_version increment wait on that if necessary.=20
>>=20
>> How common are unclean shutdowns in practice?  Do ex64/XFS/btrfs keep
>> counters in the superblocks for journal replays that can be read easily?
>>=20
>> Several useful i_version applications could be negatively impacted by
>> frequent i_version invalidation.
>>=20
>
> One would hope "not very often", but Oopses _are_ something that happens
> occasionally, even in very stable environments, and it would be best if
> what we're building can cope with them.

I was wondering if such unclean shutdown events are associated with SSD
=E2=80=9Cunsafe shutdowns=E2=80=9D, as identified by the SMART counter.  I =
think those
aren't necessarily restricted to oopses or various forms of powerless
(maybe depending on file system/devicemapper configuration)?

I admit it's possible that the file system is shut down cleanly before
the kernel requests the power-off state from the firmware, but the
underlying SSD is not.

Thanks,
Florian