netdev - Re: [PATCH v2 29/29] y2038: add 64-bit time_t syscalls to all 32-bit architectures

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Message-ID: <CALCETrXqM5mhvwreN5y-9K99h1j9rs9MAVK-cNLC54s1fdHA6w@mail.gmail.com>
Date:   Fri, 18 Jan 2019 10:50:27 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     y2038@...ts.linaro.org, Linux API <linux-api@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Matt Turner <mattst88@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Michal Simek <monstr@...str.eu>,
        Paul Burton <paul.burton@...s.com>,
        Helge Deller <deller@....de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        Andrew Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        Max Filippov <jcmvbkbc@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        deepa.kernel@...il.com,
        "Eric W. Biederman" <ebiederm@...ssion.com>, firoz.khan@...aro.org,
        linux-alpha@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-ia64@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        Network Development <netdev@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v2 29/29] y2038: add 64-bit time_t syscalls to all 32-bit architectures

On Fri, Jan 18, 2019 at 8:25 AM Arnd Bergmann <arnd@...db.de> wrote:
>
> This adds 21 new system calls on each ABI that has 32-bit time_t
> today. All of these have the exact same semantics as their existing
> counterparts, and the new ones all have macro names that end in 'time64'
> for clarification.
>
> This gets us to the point of being able to safely use a C library
> that has 64-bit time_t in user space. There are still a couple of
> loose ends to tie up in various areas of the code, but this is the
> big one, and should be entirely uncontroversial at this point.
>
> In particular, there are four system calls (getitimer, setitimer,
> waitid, and getrusage) that don't have a 64-bit counterpart yet,
> but these can all be safely implemented in the C library by wrapping
> around the existing system calls because the 32-bit time_t they
> pass only counts elapsed time, not time since the epoch. They
> will be dealt with later.
>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> The one point that still needs to be agreed on is the actual
> number assignment. Following the earlier patch that added
> the sysv IPC calls with common numbers where possible, I also
> tried the same here, using consistent numbers on all 32-bit
> architectures.
>
> There are a couple of minor issues with this:
>
> - On asm-generic, we now leave the numbers from 295 to 402
>   unassigned, which wastes a small amount of kernel .data
>   segment. Originally I had asm-generic start at 300 and
>   everyone else start at 400 here, which was also not
>   perfect, and we have gone beyond 400 already, so I ended
>   up just using the same numbers as the rest here.
>
> - Once we get to 512, we clash with the x32 numbers (unless
>   we remove x32 support first), and probably have to skip
>   a few more. I also considered using the 512..547 space
>   for 32-bit-only calls (which never clash with x32), but
>   that also seems to add a bit of complexity.

I have a patch that I'll send soon to make x32 use its own table.  As
far as I'm concerned, 547 is *it*.  548 is just a normal number and is
not special.  But let's please not reuse 512..547 for other purposes
on x86 variants -- that way lies even more confusion, IMO.

--Andy