linux-kernel - Re: [PATCH -mm 4/5][AIO] - AIO completion signal notification

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Date:	Wed, 29 Nov 2006 13:50:12 +0000
From:	Christoph Hellwig <hch@...radead.org>
To:	S?bastien Dugu? <sebastien.dugue@...l.net>
Cc:	Christoph Hellwig <hch@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-aio <linux-aio@...ck.org>, Andrew Morton <akpm@...l.org>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Zach Brown <zach.brown@...cle.com>,
	Badari Pulavarty <pbadari@...ibm.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Jean Pierre Dion <jean-pierre.dion@...l.net>
Subject: Re: [PATCH -mm 4/5][AIO] - AIO completion signal notification

On Wed, Nov 29, 2006 at 02:08:01PM +0100, S?bastien Dugu? wrote:
> On Wed, 29 Nov 2006 10:51:50 +0000, Christoph Hellwig <hch@...radead.org> wrote:
> 
> > I'm a little bit unhappy about the usage of the notify flag.  The usage
> > seems correct but very confusing:
> 
>   Well, I followed the logic from posix-timers.c, but it may be a poor
> choice ;-)
> 
>   For a start, the SIGEV_* flags are quite confusing (for me at least).
> SIGEV_SIGNAL is defined as 0, SIGEV_NONE as 1 and SIGEV_THREAD_ID as 4. I
> would rather have seen SIGEV_NONE defined as 0 to avoid all this.
> 
>   I also wish I knew why those SIGEV_* constants were defined that way.

Ah, I missed that.  It explains some of the more wierd bits.  I suspect
we should then use != SIGEV_NONE for the any kind of signal notification
bit and == SIGEV_THREAD_ID for the case where we want to deliver to
a particular thread.

But this means we only get a thread reference for SIGEV_THREAD_ID
here:

> > > +	if (notify->notify == (SIGEV_SIGNAL|SIGEV_THREAD_ID)) {
> > > +		/*
> > > +		 * This reference will be dropped in really_put_req() when
> > > +		 * we're done with the request.
> > > +		 */
> > > +		get_task_struct(target);
> > > +	}

But even use it for SIGEV_SIGNAL without SIGEV_THREAD_ID here:

> > > +	if (notify->notify & SIGEV_THREAD_ID)
> > > +		ret = send_sigqueue(notify->signo, sigq, notify->target);
> > > +	else
> > > +		ret = send_group_sigqueue(notify->signo, sigq, notify->target);

Or do I miss something?
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