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Message-ID: <8c096b3ec41b1ea3de69da038064087fd0fa481f.camel@kernel.org>
Date: Mon, 12 Sep 2022 09:49:38 -0400
From: Jeff Layton <jlayton@...nel.org>
To: Florian Weimer <fweimer@...hat.com>
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
On Mon, 2022-09-12 at 15:20 +0200, Florian Weimer wrote:
> * Jeff Layton:
>
> > On Mon, 2022-09-12 at 14:13 +0200, Florian Weimer wrote:
> > > * 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.
> > >
> >
> > 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
> “unsafe shutdowns”, 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.
>
Yeah filesystem integrity is mostly what we're concerned with here.
I think most local filesystems effectively set a flag in the superblock
that is cleared when the it's cleanly unmounted. If that flag is set
when you go to mount then you know there was a crash. We'd probably key
off of that in some way internally.
--
Jeff Layton <jlayton@...nel.org>
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