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

[Guo Ren]

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@xxxxxxxxx> 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@xxxxxxxxx> 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