linux-kernel - Re: [GIT PULL] Btrfs

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Message-ID: <CAMuHMdXMDmF4YqMWdGB8LxWsV7wr0koS47xak-isb5KAX-1sNQ@mail.gmail.com>
Date:	Fri, 13 Sep 2013 14:36:15 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Josh Boyer <jwboyer@...oraproject.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Chris Mason <chris.mason@...ionio.com>,
	Mark Fasheh <mfasheh@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-btrfs <linux-btrfs@...r.kernel.org>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	Linux-Arch <linux-arch@...r.kernel.org>
Subject: Re: [GIT PULL] Btrfs

On Fri, Sep 13, 2013 at 2:15 PM, Russell King <rmk@....linux.org.uk> wrote:
> On Fri, Sep 13, 2013 at 07:53:21AM -0400, Josh Boyer wrote:
>> I'm not an ARM expert, so I don't know if ARM should use the
>> asm-generic implementations, or just use __get_user/__put_user in all
>> cases.  I've CC'd rmk.
>
> Why do we have uaccess-unaligned.h ?  Normally, these kinds of things
> are spawned by architectures which have problems with unaligned accesses,
> ARM being one of them, but afaik we've never need this.
>
> With the kernel-side trapping of unaligned accesses on older hardware,
> we've always dealt with the normal accessor faulting.
>
> From what I can tell in the git history, these unaligned put_user and
> get_user have existed all the way back to the dawn of git use.
>
> Can someone enlighten me why we have them?

You removed the answer when trimming the quoted part:

| "Btrfs is the first user of __put_user_unaligned() outside the compat code,

 __put_user_unaligned() is used in fs/compat.c, presumably because
alignment restrictions may differ between 32- and 64-bit versions of the
same CPU family.

No one seems to actully use __get_user_unaligned().

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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