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

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Date:   Thu, 25 Aug 2016 17:52:11 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Yury Norov <ynorov@...iumnetworks.com>
Cc:     Andreas Schwab <schwab@...e.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 Monday, August 15, 2016 5:30:28 PM CEST Yury Norov wrote:
> 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...

I've lost context here, but let me try to recall what we had
discussed in the past:

- native 32-bit architectures are handled using CONFIG_ARCH_32BIT_OFF_T
- native 64-bit architectures keep setting the flag.
- compat 32-bit architectures need special cases, but the only one
  that exists is tile, which has to keep not setting O_LARGEFILE
  while new compat architectures (ilp32) should set it.
 
> 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?

The change in arch/tile/kernel/compat.c can either come before the
below change, or in the same patch, but not later.

	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
>