linux-kernel - Re: [syzbot] [hfs?] WARNING in hfs_write

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Date:   Fri, 21 Jul 2023 11:03:28 +1000 (AEST)
From:   Finn Thain <fthain@...ux-m68k.org>
To:     Dave Chinner <david@...morbit.com>
cc:     Jeff Layton <jlayton@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Viacheslav Dubeyko <slava@...eyko.com>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        syzbot <syzbot+7bb7cd3595533513a9e7@...kaller.appspotmail.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        christian.brauner@...ntu.com,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com,
        ZhangPeng <zhangpeng362@...wei.com>,
        linux-m68k@...ts.linux-m68k.org,
        debian-ports <debian-ports@...ts.debian.org>
Subject: Re: [syzbot] [hfs?] WARNING in hfs_write_inode

On Fri, 21 Jul 2023, Dave Chinner wrote:

> > I suspect that this is one of those catch-22 situations: distros are 
> > going to enable every feature under the sun. That doesn't mean that 
> > anyone is actually _using_ them these days.

I think the value of filesystem code is not just a question of how often 
it gets executed -- it's also about retaining access to the data collected 
in archives, museums, galleries etc. that is inevitably held in old 
formats.

> 
> We need to much more proactive about dropping support for unmaintained 
> filesystems that nobody is ever fixing despite the constant stream of 
> corruption- and deadlock- related bugs reported against them.
> 

IMO, a stream of bug reports is not a reason to remove code (it's a reason 
to revert some commits).

Anyway, that stream of bugs presumably flows from the unstable kernel API, 
which is inherently high-maintenance. It seems that a stable API could be 
more appropriate for any filesystem for which the on-disk format is fixed 
(by old media, by unmaintained FLOSS implementations or abandoned 
proprietary implementations).

Being in userspace, I suppose FUSE could be a stable API though I imagine 
it's not ideal in the sense that migrating kernel code there would be 
difficult. Maybe userspace NFS 4 would be a better fit? (I've no idea, I'm 
out of my depth in /fs...)

Ideally, kernel-to-userspace code migration would be done with automatic 
program transformation -- otherwise it would become another stream of 
bugs.