Date:   Wed, 23 Feb 2022 09:48:26 -0500 (EST)
From:   Byron Stanoszek <gandalf@...ds.org>
To:     Dave Chinner <david@...morbit.com>
cc:     Jan Kara <jack@...e.cz>, Matthew Wilcox <willy@...radead.org>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        reiserfs-devel@...r.kernel.org
Subject: Re: Is it time to remove reiserfs?

On Wed, 23 Feb 2022, Dave Chinner wrote:
> On Tue, Feb 22, 2022 at 11:04:08AM +0100, Jan Kara wrote:
>> Hello!
>>
>> On Sun 20-02-22 12:13:04, Matthew Wilcox wrote:
>>> Keeping reiserfs in the tree has certain costs.  For example, I would
>>> very much like to remove the 'flags' argument to ->write_begin.  We have
>>> the infrastructure in place to handle AOP_FLAG_NOFS differently, but
>>> AOP_FLAG_CONT_EXPAND is still around, used only by reiserfs.
>>>
>>> Looking over the patches to reiserfs over the past couple of years, there
>>> are fixes for a few syzbot reports and treewide changes.  There don't
>>> seem to be any fixes for user-spotted bugs since 2019.  Does reiserfs
>>> still have a large install base that is just very happy with an old
>>> stable filesystem?  Or have all its users migrated to new and exciting
>>> filesystems with active feature development?
>>>
>>> We've removed support for senescent filesystems before (ext, xiafs), so
>>> it's not unprecedented.  But while I have a clear idea of the benefits to
>>> other developers of removing reiserfs, I don't have enough information to
>>> weigh the costs to users.  Maybe they're happy with having 5.15 support
>>> for their reiserfs filesystems and can migrate to another filesystem
>>> before they upgrade their kernel after 5.15.
>>>
>>> Another possibility beyond outright removal would be to trim the kernel
>>> code down to read-only support for reiserfs.  Most of the quirks of
>>> reiserfs have to do with write support, so this could be a useful way
>>> forward.  Again, I don't have a clear picture of how people actually
>>> use reiserfs, so I don't know whether it is useful or not.
>>>
>>> NB: Please don't discuss the personalities involved.  This is purely a
>>> "we have old code using old APIs" discussion.
>>
>> So from my distro experience installed userbase of reiserfs is pretty small
>> and shrinking. We still do build reiserfs in openSUSE / SLES kernels but
>> for enterprise offerings it is unsupported (for like 3-4 years) and the module
>> is not in the default kernel rpm anymore.
>>
>> So clearly the filesystem is on the deprecation path, the question is
>> whether it is far enough to remove it from the kernel completely. Maybe
>> time to start deprecation by printing warnings when reiserfs gets mounted
>> and then if nobody yells for year or two, we'll go ahead and remove it?
>
> Yup, I'd say we should deprecate it and add it to the removal
> schedule. The less poorly tested legacy filesystem code we have to
> maintain the better.
>
> Along those lines, I think we really need to be more aggressive
> about deprecating and removing filesystems that cannot (or will not)
> be made y2038k compliant in the new future. We're getting to close
> to the point where long term distro and/or product development life
> cycles will overlap with y2038k, so we should be thinking of
> deprecating and removing such filesystems before they end up in
> products that will still be in use in 15 years time.
>
> And just so everyone in the discussion is aware: XFS already has a
> deprecation and removal schedule for the non-y2038k-compliant v4
> filesystem format. It's officially deprecated right now, we'll stop
> building kernels with v4 support enabled by default in 2025, and
> we're removing the code that supports the v4 format entirely in
> 2030.

For what it's worth, I have a number of production servers still using
Reiserfs, which I regularly maintain by upgrading to the latest Linux kernel
annually (mostly to apply security patches). I figured this filesystem would
still be available for several more years, since it's not quite y2038k yet.

I originally installed Reiserfs on these systems as early as 2005 due to the
tail-packing feature, which saved space with many small files on older
harddrives. Since then, I witnessed the development of ext4, and then btrfs.
For a long time, these newer filesystems had occasional reports of instabilities
and lost data, and so I shied away from using them. Meanwhile, Reiserfs reached
a level of maturity and no longer had active development on it, except for the
occasional bugfix. I felt this was a filesystem I could trust going forward
(despite its relative slowness), even after popular Linux distributions
eventually dropped it from being installed by default.

I have only recently begun to use XFS on newer installs, only since the XFS
developers added bigtime support for y2038k. But for existing installs, I ask
that we keep Reiserfs supported in the kernel a little longer. Perhaps use the
same deprecation schedule that was picked for XFS v4 (roughly 10 years of
deprecation before eventual removal)?

Thanks,
  -Byron

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