Re: [PATCH v2 00/10] posix_clocks: Prepare syscalls for 64 bit time_t conversion

From: Arnd Bergmann <arnd@arndb.de>
To: Deepa Dinamani <deepa.kernel@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	John Stultz <john.stultz@linaro.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	y2038 Mailman List <y2038@lists.linaro.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Chris Metcalf <cmetcalf@mellanox.com>,
	cohuck@redhat.com, David Miller <davem@davemloft.net>,
	Helge Deller <deller@gmx.de>,
	devel@driverdev.osuosl.org, gerald.schaefer@de.ibm.com,
	gregkh <gregkh@linuxfoundation.org>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Jan Hoeppner <hoeppner@linux.vnet.ibm.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"James E.J. Bottomley" <jejb@parisc-linux.org>,
	Julian
Subject: Re: [PATCH v2 00/10] posix_clocks: Prepare syscalls for 64 bit time_t conversion
Date: Wed, 29 Nov 2017 22:12:23 +0100	[thread overview]
Message-ID: <CAK8P3a2ho3S3NYp4VL7kOAk-bg3bsUmLaJJVEvNfzPoEue3v3w@mail.gmail.com> (raw)
In-Reply-To: <CABeXuvrtQfSsOipGTnfmONXS45Dqxy4_T7MAcfO4VajoSycW4w@mail.gmail.com>

On Wed, Nov 29, 2017 at 12:17 AM, Deepa Dinamani <deepa.kernel@gmail.com> wrote:
> On Tue, Nov 28, 2017 at 6:17 AM, Arnd Bergmann <arnd@arndb.de> wrote:
>> On Mon, Nov 27, 2017 at 11:29 PM, Deepa Dinamani <deepa.kernel@gmail.com> wrote:
> Right. There are three options:
>
> 1. Use two configs to identify which syscalls need not be supported by
> new architectures.
> In this case it makes sense to say LEGACY_TIME_SYSCALLS and
> COMPAT_32BIT_TIME both need to be disabled for new architectures. And,
> I can reword the config to what you mention below.
>
> 2. Make the LEGACY_TIME_SYSCALLS eliminate non y2038 safe syscalls
> mentioned below only.
> In this case only the native and compat functions of the below
> mentioned syscalls need to be identified by the config. I like this
> option as this clearly identifies which syscalls are deprecated and do
> not have a 64 bit counterpart. Not all architectures need to support
> turning this off.
>
> 3. If we don't need either 1 or 2, then we could stick with what we
> have today in the series as CONFIG_64BIT_TIME will be deleted and they
> only need #ifdef CONFIG_64BIT.
>
> Let me know if anyone prefers something else.

I think I prefer to have both LEGACY_TIME_SYSCALLS to guard
the native deprecated syscalls (disabled on 32-bit architectures after
the conversion, and enabled on 64-bit architectures until
we merge the next one), and COMPAT_32BIT_TIME to guard the
compat versions of both the deprecated and the non-deprecated
syscalls (enabled on all existing 32-bit architectures after the
conversion, and on 64-bit architectures if they provide a compat
mode for the former).

Those two are not symmetric, but I think those are the most
common combinations, and the Kconfig symbol helps document
what they are.

There is one more category for things like io_getevents() and
rt_sigtimedwait that also need two separate compat versions,
one for 32-bit time_t and one for 64-bit time_t, but it seems better
to deal with those case-by-case rather than introducing another
Kconfig symbol.

        Arnd