linux-ext4 - Re: [man-pages RFC PATCH v4] statx, inode: document the new STATX_INO

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Date:   Mon, 12 Sep 2022 14:13:05 +0200
From:   Florian Weimer <fweimer@...hat.com>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     "J. Bruce Fields" <bfields@...ldses.org>,
        Theodore Ts'o <tytso@....edu>, Jan Kara <jack@...e.cz>,
        NeilBrown <neilb@...e.de>, adilger.kernel@...ger.ca,
        djwong@...nel.org, david@...morbit.com, trondmy@...merspace.com,
        viro@...iv.linux.org.uk, zohar@...ux.ibm.com, xiubli@...hat.com,
        chuck.lever@...cle.com, lczerner@...hat.com, brauner@...nel.org,
        linux-man@...r.kernel.org, linux-api@...r.kernel.org,
        linux-btrfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, ceph-devel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-xfs@...r.kernel.org
Subject: Re: [man-pages RFC PATCH v4] statx, inode: document the new
 STATX_INO_VERSION field

* Jeff Layton:

> To do this we'd need 2 64-bit fields in the on-disk and in-memory 
> 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.
>
> Would there be a way to ensure that the new s_version_max value has made
> 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. 

How common are unclean shutdowns in practice?  Do ex64/XFS/btrfs keep
counters in the superblocks for journal replays that can be read easily?

Several useful i_version applications could be negatively impacted by
frequent i_version invalidation.

Thanks,
Florian