linux-kernel - Re: Update of file offset on write() etc. is non-atomic with I/O

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Date:	Mon, 3 Mar 2014 15:59:36 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	George Spelvin <linux@...izon.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Update of file offset on write() etc. is non-atomic with I/O

On Mon, Mar 3, 2014 at 3:42 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> On Mon, Mar 03, 2014 at 03:34:43PM -0800, Linus Torvalds wrote:
>>
>> (Side note: I think sparc or something doesn't support it, and may
>> return things in memory. I can't really seem to find it in myself to
>> care)
>
> sparc64 actually does support that.  So does amd64, and, with explicit
> flag, i386.  No other more or less general purpose architecture does.
>
> Not ppc.  Not mips.  Not arm.  I think that some of those are worth
> caring about...

I doubt it's worth caring about. Even when passing things in memory,
the end result isn't that much worse than the fget_light() model that
passes just one of the two fields in memory.

If the ARM/PPC people end up caring, they could add the struct-return
support to gcc. It should be basically just adding the flag for
enabling the calling convention - the core gcc support is obviously
all there, and it's just an issue of whether the calling conventions
allow it or not.

             Linus
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