linux-kernel - Re: [RFC PATCH 3/6] fs: provide generic compat_sys

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Date:   Sun, 18 Mar 2018 10:40:22 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Dominik Brodowski <linux@...inikbrodowski.net>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-arch <linux-arch@...r.kernel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        linux-mips <linux-mips@...ux-mips.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        ppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        linux-s390 <linux-s390@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        sparclinux@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Jiri Slaby <jslaby@...e.com>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [RFC PATCH 3/6] fs: provide generic compat_sys_p{read,write}64() implementations

Honestly, I think the patches like this are disgusting:

On Sun, Mar 18, 2018 at 9:10 AM, Dominik Brodowski
<linux@...inikbrodowski.net> wrote:
> +#ifdef __ARCH_WANT_COMPAT_SYS_PREADWRITE64
> +#if defined(__ARCH_WANT_COMPAT_SYS_WITH_PADDING) && \
> +       defined(__ARCH_WANT_LE_COMPAT_SYS)
> +COMPAT_SYSCALL_DEFINE6(pread64, unsigned int, fd, char __user *, ubuf,
> +                      u32, count, u32, padding, u32, poslo, u32, poshi)
> +#elif defined(__ARCH_WANT_COMPAT_SYS_WITH_PADDING) && \
> +       !defined(__ARCH_WANT_LE_COMPAT_SYS)
> +COMPAT_SYSCALL_DEFINE6(pread64, unsigned int, fd, char __user *, ubuf,
> +                      u32, count, u32, padding, u32, poshi, u32, poslo)
> +#elif !defined(__ARCH_WANT_COMPAT_SYS_WITH_PADDING) && \
> +       defined(__ARCH_WANT_LE_COMPAT_SYS)
> +COMPAT_SYSCALL_DEFINE5(pread64, unsigned int, fd, char __user *, ubuf,
> +                      u32, count, u32, poslo, u32, poshi)
> +#else /* no padding, big endian */
> +COMPAT_SYSCALL_DEFINE5(pread64, unsigned int, fd, char __user *, ubuf,
> +                      u32, count, u32, poshi, u32, poslo)
> +#endif
> +{
> +#ifdef CONFIG_S390
> +       if ((compat_ssize_t) count < 0)
> +               return -EINVAL;
> +#endif /* CONFIG_S390 */

and we should just keep code like this entirely architecture-dependent.

It doesn't save all that many lines:

 19 files changed, 97 insertions(+), 106 deletions(-)

and the lines it adds are an unreadable mess compared to the lines it removes.

So please keep the high/low/padding stuff in the arch wrapper, and
just make them use "do_pwrite64()" and friends instead (or
"kern_pwrite64()", or whatever we ended up using as the kernel naming
for in-kernel system call wrappers).

                Linus