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Date:   Wed, 23 Feb 2022 10:28:39 -0500 (EST)
From:   Byron Stanoszek <gandalf@winds.org>
To:     Dave Chinner <david@fromorbit.com>
cc:     Jan Kara <jack@suse.cz>, Matthew Wilcox <willy@infradead.org>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        reiserfs-devel@vger.kernel.org
Subject: Re: Is it time to remove reiserfs?
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References: <YhIwUEpymVzmytdp@casper.infradead.org> <20220222100408.cyrdjsv5eun5pzij@quack3.lan> <20220222221614.GC3061737@dread.disaster.area> <3ce45c23-2721-af6e-6cd7-648dc399597@winds.org>
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On Wed, 23 Feb 2022, Byron Stanoszek wrote:
> 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)?

Sorry, I meant to say 5 years here, not 10.

Thanks,
  -Byron