From mboxrd@z Thu Jan  1 00:00:00 1970
From: Takashi Iwai <tiwai@suse.de>
Subject: Re: [PATCH] ALSA: control: confirm to return all
	identical information in 'activate' event data
Date: Mon, 09 Feb 2015 17:18:49 +0100
Message-ID: <s5h8ug7rrbq.wl-tiwai@suse.de>
References: <1423494126-24054-1-git-send-email-o-takashi@sakamocchi.jp>
 <s5hsiefrtni.wl-tiwai@suse.de> <54D8D9CB.5080709@sakamocchi.jp>
 <s5hh9uvrs2c.wl-tiwai@suse.de>
Mime-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka")
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <alsa-devel-bounces@alsa-project.org>
Received: from mx2.suse.de (cantor2.suse.de [195.135.220.15])
 by alsa0.perex.cz (Postfix) with ESMTP id 927B0260506
 for <alsa-devel@alsa-project.org>; Mon,  9 Feb 2015 17:18:52 +0100 (CET)
In-Reply-To: <s5hh9uvrs2c.wl-tiwai@suse.de>
List-Unsubscribe: <http://mailman.alsa-project.org/mailman/options/alsa-devel>,
 <mailto:alsa-devel-request@alsa-project.org?subject=unsubscribe>
List-Archive: <http://mailman.alsa-project.org/pipermail/alsa-devel/>
List-Post: <mailto:alsa-devel@alsa-project.org>
List-Help: <mailto:alsa-devel-request@alsa-project.org?subject=help>
List-Subscribe: <http://mailman.alsa-project.org/mailman/listinfo/alsa-devel>,
 <mailto:alsa-devel-request@alsa-project.org?subject=subscribe>
Errors-To: alsa-devel-bounces@alsa-project.org
Sender: alsa-devel-bounces@alsa-project.org
To: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Cc: alsa-devel@alsa-project.org, clemens@ladisch.de
List-Id: alsa-devel@alsa-project.org

At Mon, 09 Feb 2015 17:02:51 +0100,
Takashi Iwai wrote:
> 
> At Tue, 10 Feb 2015 01:01:15 +0900,
> Takashi Sakamoto wrote:
> > 
> > On Feb 10 2015 00:28, Takashi Iwai wrote:
> > > At Tue, 10 Feb 2015 00:02:06 +0900,
> > > Takashi Sakamoto wrote:
> > >>
> > >> When event originator doesn't set numerical ID in identical information,
> > >> the event data includes no numerical ID, thus userspace applications
> > >> cannot identify the control just by unique ID in event data.
> > >>
> > >> This commit fix this bug so as the event data includes all of identical
> > >> information.
> > >>
> > >> Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
> > >
> > > You can't overwrite id pointer in this case.  It's a caller's object.
> > 
> > Exactly. I missed it...
> > 
> > > One way to fix would be to copy the id instance.  Another way would be
> > > to change up/down_write() with _read(), and include snd_ctl_notify()
> > > call with kctl->id inside the semaphore lock.
> > >
> > > The former would be less changes but consume the stack significantly.
> > 
> > If any sub-effects are allowed, we can use caller's data via the 
> > pointer, like:
> > memcpy(id, &kctl->id, sizeof(struct snd_ctl_elem_id);
> > Then:
> > snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_INFO, id);
> 
> That's what I suggested as the first example.

... and I think this is a better way in the end.  Simpler, better.
The stack usage is very likely acceptable.


Takashi