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 23:54:56 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
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 03, 2014 at 11:39:02PM +0000, Al Viro wrote:
> On Mon, Mar 03, 2014 at 03:23:55PM -0800, Linus Torvalds wrote:
> 
> > 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?
> 
> do_sendfile() is also there and this one is even more unpleasant ;-/
> We probably can ignore that one (until POSIX learns of its existence),
> thouhg...

OK, other than read/write/readv/writev/lseek we have only sendfile{,64} and
splice; everything else either deals with struct file that is guaranteed to
be not accessible by any syscall (e.g. coredump code) or is not a regular
file.  So the only question is whether we care for syscalls that are
out of scope for POSIX.
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