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 15:23:55 -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 2:55 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> I think I'll respin this with the compat readv/writev case fixed and
> with the bitfield replaced with an "unsigned int" that we just do
> bitops by hand on. Because that code generation makes me feel slightly
> ill.

Ok, how about this version? For some reason I thought the compat
functions for readv/writev were in fs/compat.c, but they are there in
the same fs/read_write.c, so I didn't need to move the helper
functions away.

This just uses a "flags" field, and we currently only have two bits
that we use: FDPUT_FPUT and FDPUT_POS_UNLOCK. The first patch knows
that "fget_light()" writes 0/1 for that, which is the same as the
FDPUT_FPUT bit. I didn't bother to comment on it or clean it up, since
the second patch just removes that whole fget_light() mess.

Comments?

           Linus

View attachment "0001-vfs-atomic-f_pos-accesses-as-per-POSIX.patch" of type "text/x-patch" (8681 bytes)

View attachment "0002-vfs-get-rid-of-old-legacy-f-get-put-_-raw_-_light-in.patch" of type "text/x-patch" (4211 bytes)