linux-kernel - Re: RFC: reject unknown open flags

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Message-ID: <ec12e823-5c32-3269-039a-1b97ab3d4819@cs.ucla.edu>
Date:   Thu, 30 Mar 2017 12:02:04 -0700
From:   Paul Eggert <eggert@...ucla.edu>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Linux API <linux-api@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        libc-alpha <libc-alpha@...rceware.org>
Subject: Re: RFC: reject unknown open flags

On 03/30/2017 11:19 AM, Linus Torvalds wrote:
> like "dd" growing an atomic flag and setting it on stdout),

'dd' typically assumes that if a flag O_FOO is not #defined by 
<fcntl.h>, then 'dd' can "#define O_FOO 0" and the rest of dd's code can 
assume O_FOO works "well enough" on older systems. I hope this 
backward-compatibility hack will suffice for O_ATOMIC too.

> I'm assuming you'd also possible want to be able to use F_SETFL to set
> O_ATOMIC after the fact

Just for fun, one thread can set O_ATOMIC at the same time another 
thread is doing a 'write'....