linux-kernel - Re: [PATCH V4 00/27] C-SKY(csky) Linux Kernel Port

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Message-ID: <20180914160231.GA32161@guoren-Inspiron-7460>
Date:   Sat, 15 Sep 2018 00:02:32 +0800
From:   Guo Ren <ren_guo@...ky.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Jason Cooper <jason@...edaemon.net>,
        DTML <devicetree@...r.kernel.org>,
        andrea.parri@...rulasolutions.com,
        Peter Zijlstra <peterz@...radead.org>,
        c-sky_gcc_upstream@...ky.com, gnu-csky@...tor.com,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        wbx@...ibc-ng.org, Greentime Hu <green.hu@...il.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH V4 00/27] C-SKY(csky) Linux Kernel Port

On Fri, Sep 14, 2018 at 04:46:56PM +0200, Arnd Bergmann wrote:
> On Fri, Sep 14, 2018 at 4:37 PM Guo Ren <ren_guo@...ky.com> wrote:
> > On Wed, Sep 12, 2018 at 04:30:36PM +0200, Arnd Bergmann wrote:
> > > On Wed, Sep 12, 2018 at 3:25 PM Guo Ren <ren_guo@...ky.com> wrote:
> > >
> > > One big question for me is what to do about time_t. Deepa and I are
> > > in the process of finalizing the system call ABI for 32-bit architectures
> > > with 64-bit time_t, but we are not done yet and it won't be complete
> > > for 4.20. If you target 4.21, that could be a chance to make csky the
> > > first architecture to only need the 64-bit time_t interface, with the
> > > corresponding user space changes.
> > y2038 is very important and csky32 has the issue. But 4.21 is too late for
> > us, we really want to get into kernel.org as soon as possible.
> > We could remove 32-bit time_t in future.
> 
> Not really: the way we deal with user-visible APIs in the kernel, it's
> practically impossible to remove something that was working before,
> since there may always be users relying on it. This is why it is so
> important that we get the ABI right at the first try.
> 
> We can always add new ABIs later, and that's what we're doing with
> all the other 32-bit architectures as well: each system call that takes a
> 32-bit time_t argument also needs to get the corresponding 64-bit
> replacement, and then we have to keep them both around.
> 
> However, once the 64-bit syscalls are there, you don't need to
> use them, so if you merge the glibc port after both csky and
> the time64 syscalls are merged upstream, you can choose
> to only support the time64 syscalls rather than making it a compile
> time decision in each application. If you merge the glibc port
> before migrating to 64-bit syscalls, glibc will also have to support
> both indefinitely for compatibility with existing binaries.
> 
> One level below that, you can of course choose to build
> a distro with only 64-bit time_t regardless of whether there
> is still support for 32-bit time_t in kernel and glibc or not.
Do you mean I could merge kernel port into linux-4.19 or linux-4.20.
But let glibc merged after linux-4.21 and csky glibc only support
time64 syscalls ?

Best Regards
 Guo Ren