From mboxrd@z Thu Jan  1 00:00:00 1970
From: Takashi Iwai <tiwai@suse.de>
Subject: Re: [PATCH - alsa-lib 1/1] Change card/pid get
	functions to return -ENOSYS if the kernel is too old
Date: Mon, 06 Jun 2016 16:01:21 +0200
Message-ID: <s5hr3camn66.wl-tiwai@suse.de>
References: <1459532030-6387-1-git-send-email-agoode@google.com>
 <20160401211558.GA20661@mail.zuhause>
 <s5hpou5a0g0.wl-tiwai@suse.de>
 <CAOf41NmK6V1MMUrQ=UwO=nttYuk3a5b63jH5VTBxeJM9px1yow@mail.gmail.com>
 <20160407201041.GB26683@mail.zuhause>
 <s5hpou0mm87.wl-tiwai@suse.de> <5707AA7C.5030804@perex.cz>
 <s5hegagmekc.wl-tiwai@suse.de>
 <CAOf41N=vdhUu+y08JZLs7c=DL_LYx4wQgxxnMkWw-eQCUT-etw@mail.gmail.com>
 <20160408175633.GA14123@mail.zuhause>
 <CAOf41Nn-vtZp+po5=_5CwejXh+5Q7LyAXeZav82+T3jf1tBJ7A@mail.gmail.com>
 <CAOf41Nk+_j_AXd9PXOKd6HV3Tv7G+Nsf35+9p0NNrOEwGyN1SQ@mail.gmail.com>
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 (mx2.suse.de [195.135.220.15])
 by alsa0.perex.cz (Postfix) with ESMTP id B741B265759
 for <alsa-devel@alsa-project.org>; Mon,  6 Jun 2016 16:01:22 +0200 (CEST)
In-Reply-To: <CAOf41Nk+_j_AXd9PXOKd6HV3Tv7G+Nsf35+9p0NNrOEwGyN1SQ@mail.gmail.com>
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: Adam Goode <agoode@google.com>
Cc: alsa-devel@alsa-project.org, Martin Koegler <martin.koegler@chello.at>
List-Id: alsa-devel@alsa-project.org

On Mon, 06 Jun 2016 15:57:33 +0200,
Adam Goode wrote:
> 
> On Fri, Apr 8, 2016 at 3:53 PM, Adam Goode <agoode@google.com> wrote:
> 
> > On Fri, Apr 8, 2016 at 1:56 PM, Martin Koegler <martin.koegler@chello.at>
> > wrote:
> >
> >> On Fri, Apr 08, 2016 at 11:21:57AM -0400, Adam Goode wrote:
> >> > So there are 2 alternatives I can think of:
> >> >
> >> > option 1: introduce snd_seq_client_info_get_pid_2() and leave the
> >> existing
> >> > function alone. This new function can return a new constant,
> >> > SND_SEQ_CLIENT_INFO_PID_UNKNOWN for missing kernel support. Same for
> >> card.
> >> > option 2: introduce snd_seq_client_info_pid_known() that returns a bool
> >> if
> >> > there is kernel support. Same for card.
> >>
> >> I wouldn't implement option 1. Using that methode for API changes will
> >> result in lots of rarely used functions.
> >>
> >> Chrome will probable need that information to enable a fallback-code - if
> >> a application has no fallback code,
> >> it has no need for different returncodes. In a few years, most
> >> distributions will likely ship kernel including that functions,
> >> so there is no need to for fallback-code and the kernel support check any
> >> more.
> >>
> >> Why not a snd_seq_client_info_get_capatibilites() returing bit flags:
> >> .._CAP_CARD_NUMBER | .._CAP_PID ?
> >>
> >>
> > This approach is fine by me as well, though it does introduce more
> > constants and bitwise logic.
> >
> >
> Since returning to this problem after a while, I've realized that we don't
> need any changes at all to alsa-lib. This test is equivalent to what is
> needed:
> 
> snd_seq_get_client_info(seq, info); // get our client's info
> bool client_pid_supported = snd_seq_client_info_get_pid(info) != -1; // do
> we know our own PID?

Ah, yes, it works.  I thought of another, e.g. checking /dev/sequencer
version ioctl, but yours works more nicely.

> It might be helpful to put this into the documentation, but otherwise I
> think this is fine.

A patch is always welcome :)


thanks,

Takashi