linux-kernel - Re: [Y2038] [PATCH 04/20] mount: Add mount warning for impending timestamp expiry

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Message-ID: <CAK8P3a0CADLUeXvsBHNAC8ekLoo0o0uYz2arBqZ=1N+Xp8HNvA@mail.gmail.com>
Date:   Mon, 12 Aug 2019 16:11:38 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Ben Hutchings <ben.hutchings@...ethink.co.uk>
Cc:     Deepa Dinamani <deepa.kernel@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>
Subject: Re: [Y2038] [PATCH 04/20] mount: Add mount warning for impending
 timestamp expiry

On Mon, Aug 12, 2019 at 3:25 PM Ben Hutchings
<ben.hutchings@...ethink.co.uk> wrote:
> On Sat, 2019-08-10 at 13:44 -0700, Deepa Dinamani wrote:
> > On Mon, Aug 5, 2019 at 7:14 AM Ben Hutchings
> > <ben.hutchings@...ethink.co.uk> wrote:
> > > On Mon, 2019-07-29 at 18:49 -0700, Deepa Dinamani wrote:
> > > > The warning reuses the uptime max of 30 years used by the
> > > > setitimeofday().
> > > >
> > > > Note that the warning is only added for new filesystem mounts
> > > > through the mount syscall. Automounts do not have the same warning.
> > > [...]
> > >
> > > Another thing - perhaps this warning should be suppressed for read-only
> > > mounts?
> >
> > Many filesystems support read only mounts only. We do fill in right
> > granularities and limits for these filesystems as well. In keeping
> > with the trend, I have added the warning accordingly. I don't think I
> > have a preference either way. But, not warning for the red only mounts
> > adds another if case. If you have a strong preference, I could add it
> > in.
>
> It seems to me that the warning is needed if there is a possibility of
> data loss (incorrect timestamps, potentially leading to incorrect
> decisions about which files are newer).  This can happen only when a
> filesystem is mounted read-write, or when a filesystem image is
> created.
>
> I think that warning for read-only mounts would be an annoyance to
> users retrieving files from old filesystems.

I agree, the warning is not helpful for read-only mounts. An earlier
plan was to completely disallow writable mounts that might risk an
overflow (in some configurations at least). The warning replaces that
now, and I think it should also just warn for the cases that would
otherwise have been dangerous.

       Arnd