Re: [PATCH] Revert "asm-generic: Remove unneeded __ARCH_WANT_SYS_LLSEEK macro"

From: Arnd Bergmann <arnd@arndb.de>
To: Christoph Hellwig <hch@infradead.org>
Cc: Rich Felker <dalias@libc.org>,
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Subject: Re: [PATCH] Revert "asm-generic: Remove unneeded __ARCH_WANT_SYS_LLSEEK macro"
Date: Sat, 31 Aug 2019 15:44:15 +0200	[thread overview]
Message-ID: <CAK8P3a2xDT1FC-vA3S55_TYt_g+wZHHg4cCGLdWd=Sk7Hmg-bA@mail.gmail.com> (raw)
In-Reply-To: <20190831083849.GA24644@infradead.org>

On Sat, Aug 31, 2019 at 10:39 AM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Fri, Aug 30, 2019 at 09:54:43PM +0200, Arnd Bergmann wrote:
> > > -#if !defined(CONFIG_64BIT) || defined(CONFIG_COMPAT)
> > > +#ifdef __ARCH_WANT_SYS_LLSEEK
> > >  SYSCALL_DEFINE5(llseek, unsigned int, fd, unsigned long, offset_high,
> > >                 unsigned long, offset_low, loff_t __user *, result,
> > >                 unsigned int, whence)
> >
> > However, only reverting the patch will now break all newly added
> > 32-bit architectures that don't define __ARCH_WANT_SYS_LLSEEK:
> > at least nds32 and riscv32 come to mind, not sure if there is another.
> >
> > I think the easiest way however would be to combine the two checks
> > above and make it
> >
> > #if !defined(CONFIG_64BIT) || defined(CONFIG_COMPAT) ||
> > defined(__ARCH_WANT_SYS_LLSEEK)
> >
> > and then only set __ARCH_WANT_SYS_LLSEEK for powerpc.
>
> I'd much rather introduce a CONFIG_SYS_LLSEEK Kconfig symbol, selected
> by CONFIG_64BIT and CONFIG_COMPAT by default, plus manually by powerpc.

The reason we currently use  __ARCH_WANT_SYS_* for all the other conditional
system calls is that these macros can be put into the uapi file for use by
include/uapi/asm/unistd.h, which is not possible with CONFIG_*
symbols.

This is not a problem for llseek, but it would be slightly inconsistent.

Nitesh is trying to convert include/uapi/asm/unistd.h into syscall.tbl format,
after that is done, we can probably change all the __ARCH_WANT_SYS_*
into config symbols.

       Arnd