linux-kernel - Re: [PATCH V7 03/20] compat: consolidate the compat

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Date:   Mon, 28 Feb 2022 13:51:03 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Guo Ren <guoren@...nel.org>
Cc:     David Laight <David.Laight@...lab.com>,
        "palmer@...belt.com" <palmer@...belt.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "anup@...infault.org" <anup@...infault.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "liush@...winnertech.com" <liush@...winnertech.com>,
        "wefu@...hat.com" <wefu@...hat.com>,
        "drew@...gleboard.org" <drew@...gleboard.org>,
        "wangjunqiang@...as.ac.cn" <wangjunqiang@...as.ac.cn>,
        "hch@....de" <hch@....de>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-csky@...r.kernel.org" <linux-csky@...r.kernel.org>,
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        "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
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        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH V7 03/20] compat: consolidate the compat_flock{,64} definition

On Mon, Feb 28, 2022 at 1:13 PM Guo Ren <guoren@...nel.org> wrote:
> On Mon, Feb 28, 2022 at 8:02 PM David Laight <David.Laight@...lab.com> wrote:
> > From: Guo Ren Sent: 28 February 2022 11:52
> > > On Mon, Feb 28, 2022 at 2:40 PM David Laight <David.Laight@...lab.com> wrote:
> > > > ...
> > > > > +struct compat_flock64 {
> > > > > +     short           l_type;
> > > > > +     short           l_whence;
> > > > > +     compat_loff_t   l_start;
> > > > > +     compat_loff_t   l_len;
> > > > > +     compat_pid_t    l_pid;
> > > > > +#ifdef __ARCH_COMPAT_FLOCK64_PAD
> > > > > +     __ARCH_COMPAT_FLOCK64_PAD
> > > > > +#endif
> > > > > +} __ARCH_COMPAT_FLOCK64_PACK;
> > > > > +
> > > >
> > > > Provided compat_loff_t are correctly defined with __aligned__(4)
> > > See include/asm-generic/compat.h
> > >
> > > typedef s64 compat_loff_t;
> > >
> > > Only:
> > > #ifdef CONFIG_COMPAT_FOR_U64_ALIGNMENT
> > > typedef s64 __attribute__((aligned(4))) compat_s64;
> > >
> > > So how do you think compat_loff_t could be defined with __aligned__(4)?
> >
> > compat_loff_t should be compat_s64 not s64.
> >
> > The same should be done for all 64bit 'compat' types.
> Changing
> typedef s64 compat_loff_t;
> to
> typedef compat_s64 compat_loff_t;
>
> should be another patch and it affects all architectures, I don't
> think we should involve it in this series.

Agreed, your patch (originally from Christoph) looks fine, it correctly
transforms the seven copies of the structure into a shared version.

There is always more that can be improved, but for this series,
I think you have already done enough.

> look at kernel/power/user.c:
> struct compat_resume_swap_area {
>         compat_loff_t offset;
>         u32 dev;
> } __packed;
>
> I thnk keep "typedef s64 compat_loff_t;" is a sensible choice for
> COMPAT support patchset series.

The only references to compat_loff_t that we have in the kernel
could all be simplified by defining compat_loff_t as compat_s64
instead of s64, but it has no impact on correctness here.

Let's make sure you get your series into 5.18, and then David can
follow-up with any further cleanups after that.

         Arnd