linux-kernel - Re: [Y2038] [PATCH 5/9] y2038: introduce CONFIG_64BIT

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Date:   Fri, 08 Dec 2017 18:23:28 +0000
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Deepa Dinamani <deepa.kernel@...il.com>
Cc:     y2038 Mailman List <y2038@...ts.linaro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        John Stultz <john.stultz@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [Y2038] [PATCH 5/9] y2038: introduce CONFIG_64BIT_TIME

On Fri, 2017-12-08 at 09:01 -0800, Deepa Dinamani wrote:
> On Fri, Dec 8, 2017 at 8:53 AM, Ben Hutchings
> > <ben.hutchings@...ethink.co.uk> wrote:
> > On Fri, 2017-11-10 at 14:42 -0800, Deepa Dinamani wrote:
> > > From: Arnd Bergmann <arnd@...db.de>
> > > 
> > > There are a total of 53 system calls (aside from ioctl) that pass a time_t
> > > or derived data structure as an argument, and in order to extend time_t
> > > to 64-bit, we have to replace them with new system calls and keep providing
> > > backwards compatibility.
> > > 
> > > To avoid adding completely new and untested code for this purpose, we
> > > introduce a new CONFIG_64BIT_TIME symbol. Every architecture that supports
> > > new 64 bit time_t syscalls enables this config via ARCH_HAS_64BIT_TIME.
> > > 
> > > After this is done for all architectures, the CONFIG_64BIT_TIME symbol
> > > can be made a user-selected option, to enable users to build a kernel
> > > that only provides y2038-safe system calls by making 32 time_t syscalls
> > > conditionally included based on the above config.
> > 
> > I don't understand why we would want to change the semantics of
> > CONFIG_64BIT_TIME symbol from "enable 64-bit time support" to "disable
> > 32-bit time support".
> > 
> > Why not add two config symbols:
> > 
> > config 32BIT_TIME
> >         def_bool COMPAT || !64BIT
> > 
> > config 64BIT_TIME
> >         def_bool ARCH_HAS_64BIT_TIME
> > 
> > and then make 32BIT_TIME user-configurable later?
> 
> This was already discussed on the review and we have an updated version:
> 
> https://lkml.org/lkml/2017/11/27/938

Sorry, I'll move on to reviewing that.

Ben.

-- 
Ben Hutchings
Software Developer, Codethink Ltd.