linux-kernel - Re: [PATCH 01/19] compat ABI: use non-compat openat and open_by_handle

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Date:	Mon, 15 Aug 2016 17:30:28 +0300
From:	Yury Norov <ynorov@...iumnetworks.com>
To:	Andreas Schwab <schwab@...e.de>
CC:	<arnd@...db.de>, <catalin.marinas@....com>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>,
	<linux-arch@...r.kernel.org>, <libc-alpha@...rceware.org>,
	<schwidefsky@...ibm.com>, <heiko.carstens@...ibm.com>,
	<pinskia@...il.com>, <broonie@...nel.org>,
	<joseph@...esourcery.com>,
	<christoph.muellner@...obroma-systems.com>,
	<bamvor.zhangjian@...wei.com>, <szabolcs.nagy@....com>,
	<klimov.linux@...il.com>, <Nathan_Lynch@...tor.com>,
	<agraf@...e.de>, <Prasun.Kapoor@...iumnetworks.com>,
	<kilobyte@...band.pl>, <geert@...ux-m68k.org>,
	<philipp.tomsich@...obroma-systems.com>,
	<manuel.montezelo@...il.com>, <linyongting@...wei.com>,
	<maxim.kuvyrkov@...aro.org>, <davem@...emloft.net>
Subject: Re: [PATCH 01/19] compat ABI: use non-compat openat and
 open_by_handle_at variants

On Mon, Jun 27, 2016 at 09:47:38AM +0200, Andreas Schwab wrote:
> Yury Norov <ynorov@...iumnetworks.com> writes:
> 
> > The only difference is that non-compat version forces O_LARGEFILE,
> > and it should be the default behaviour for all architectures, as
> > we don't support 32-bit off_t. The only exception is tile32, that
> > continues with compat version of syscalls.
> >
> > Signed-off-by: Yury Norov <ynorov@...iumnetworks.com>
> > Acked-by: Arnd Bergmann <arnd@...db.de>
> > Acked-by: Chris Metcalf <cmetcalf@...hip.com> [for tile]
> > ---
> >  arch/tile/kernel/compat.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/arch/tile/kernel/compat.c b/arch/tile/kernel/compat.c
> > index 4912084..489ae19 100644
> > --- a/arch/tile/kernel/compat.c
> > +++ b/arch/tile/kernel/compat.c
> > @@ -94,6 +94,9 @@ COMPAT_SYSCALL_DEFINE5(llseek, unsigned int, fd, unsigned int, offset_high,
> >  #define compat_sys_readahead sys32_readahead
> >  #define sys_llseek compat_sys_llseek
> >  
> > +#define sys_openat		compat_sys_openat
> > +#define sys_open_by_handle_at	compat_sys_open_by_handle_at
> > +
> >  /* Call the assembly trampolines where necessary. */
> >  #define compat_sys_rt_sigreturn _compat_sys_rt_sigreturn
> >  #define sys_clone _sys_clone
> 
> This is a no-op.  Did you mean to add this?  Without that the testsuite
> of tar fails on ILP32.

The change you suggest below is what I originally sent at the end of
December, but that chunk was lost after one of numerous rebases probably.

http://lkml.iu.edu/hypermail/linux/kernel/1512.3/00510.html

IIRC, the only difference between this couple of syscalls and their
compat versions is that non-compat syscalls set O_LARGEFILE depending
on (BITS_PER_LONG != 32). Next patch of this series introduces
ARCH_32BIT_OFF_T config option to force O_LARGEFILE for 64-bit arches,
and all new 32-bit arches, as ARCH_32BIT_OFF_T is enabled for existing
32-bit arches explicitly.

O_LARGEFILE is controlled like this:
        -#define force_o_largefile() (BITS_PER_LONG != 32)
        +#define force_o_largefile() (!IS_ENABLED(CONFIG_ARCH_32BIT_OFF_T))

So if I restore original patch, everything will work. But my question
is: if ARCH_32BIT_OFF_T disables O_LARGEFILE for tile32 anyway, what
for we redirect native syscall handlers to compat ones? They are
looking identical...

If my understanding is correct, we can drop the change in
arch/tile/kernel/compat.c and join this patch with next one in this
series.

Chris, Arnd?

> 
> diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
> index a26415b..4dcc38d 100644
> --- a/include/uapi/asm-generic/unistd.h
> +++ b/include/uapi/asm-generic/unistd.h
> @@ -178,7 +178,7 @@ __SYSCALL(__NR_fchownat, sys_fchownat)
>  #define __NR_fchown 55
>  __SYSCALL(__NR_fchown, sys_fchown)
>  #define __NR_openat 56
> -__SC_COMP(__NR_openat, sys_openat, compat_sys_openat)
> +__SYSCALL(__NR_openat, sys_openat)
>  #define __NR_close 57
>  __SYSCALL(__NR_close, sys_close)
>  #define __NR_vhangup 58
> @@ -676,8 +676,7 @@ __SYSCALL(__NR_fanotify_mark, sys_fanotify_mark)
>  #define __NR_name_to_handle_at         264
>  __SYSCALL(__NR_name_to_handle_at, sys_name_to_handle_at)
>  #define __NR_open_by_handle_at         265
> -__SC_COMP(__NR_open_by_handle_at, sys_open_by_handle_at, \
> -	  compat_sys_open_by_handle_at)
> +__SYSCALL(__NR_open_by_handle_at, sys_open_by_handle_at)
>  #define __NR_clock_adjtime 266
>  __SC_COMP(__NR_clock_adjtime, sys_clock_adjtime, compat_sys_clock_adjtime)
>  #define __NR_syncfs 267
> -- 
> 2.9.0
> 
> 
> Andreas.
> 
> -- 
> Andreas Schwab, SUSE Labs, schwab@...e.de
> GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
> "And now for something completely different."