linux-ext4 - Re: [Y2038] [PATCH v5 2/5] vfs: Add checks for filesystem timestamp limits

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Date:   Tue, 25 Apr 2017 23:23:41 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "Theodore Ts'o" <tytso@....edu>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "adilger.kernel@...ger.ca" <adilger.kernel@...ger.ca>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [Y2038] [PATCH v5 2/5] vfs: Add checks for filesystem timestamp limits

On Tue, Apr 25, 2017 at 10:35 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Tue, Apr 25, 2017 at 1:31 PM, Arnd Bergmann <arnd@...db.de> wrote:
>>
>> Would it be ok to have a simple way of removing the time_t definition (e.g.
>> by passing '-DREQUIRE_TIME64' to the compiler, but without the Kconfig
>> option? That way, someone who wants to ship a product can at least
>> find the obvious dependencies on stuff that remains broken.
>
> How would you find them?
>
> People don't necessarily use "time_t". They might use "int" or whatever.

My main approach has been:

* Assume that all of the time_t based interfaces are broken on 32-bit systems
  (some are not, but almost all are)

* For each interface that exposes a time_t to other files, introduce a
  replacement interface that is known to work

* Change users of the old interface over to the new one, one at a time,
  while manually reviewing all other code this interacts with.

Note that the vast majority of all the in-kernel uses of time_t variables
actually use timespec or timeval structures because they require
sub-second resolution, so we already know that they cannot
accidentally get assigned to 'int'. Also, we typically replace them with
ktime_t for efficiency. In case we replace a timespec with timespec64,
we do have to be careful to ensure that no code just treats the
tv_sec member as 'int' or 'long' though.

      Arnd