[ALSA - lib 0001034]: (potential) problems introduced with the " improved stream linking and plugin code cleanups" patch by perex

[bugtrack@alsa-project.org]

A NOTE has been added to this issue.
======================================================================
<https://bugtrack.alsa-project.org/alsa-bug/view.php?id=1034> 
======================================================================
Reported By:                modax
Assigned To:                
======================================================================
Project:                    ALSA - lib
Issue ID:                   1034
Category:                   pcm - digital audio
Reproducibility:            always
Severity:                   major
Priority:                   normal
Status:                     new
======================================================================
Date Submitted:             04-03-2005 17:42 CEST
Last Modified:              04-03-2005 17:53 CEST
======================================================================
Summary:                    (potential) problems introduced with the " improved
stream linking and plugin code cleanups" patch by perex
Description: 
I'm not an alsa developer so I hadn't known anything about alsa internals
up until I started debugging alsa-lib to fix an annoying bug I was having
with alsa 1.0.9rc1 and above. I'm not sure whether my patch/suggestions
are 100% correct or the best way fix to those bugs.

The initial problem I'm refering to is described in bug#1009 note
https://bugtrack.alsa-project.org/alsa-bug/view.php?id=0004275. I narrowed my
search of the regression down to the big patch,
which was submitted to alsa-lib CVS on 2005-01-20 by perex. The patch
cleans up plugin code. Unfortunately, some things have been overlooked by
the author. Firstly, I'll start with my problem and a fix for it.

As I described in note
https://bugtrack.alsa-project.org/alsa-bug/view.php?id=0004275, I had problems
with -Dsurround51 on my
NFORCE board. The root of the problem was a combination of two plugins -
route and hooks - used in surround51 configuration. Later I learned, that
removing one of them helped, but they both wouldn't work. The portion of
code which is to blame for the regression can be seen in
hooks-channel-info-fix.patch (attached). Just compare the original
pcm_hooks.c:snd_pcm_hooks_channel_info() (before "2005-01-20" patch) and
pcm_generic.c:snd_pcm_generic_channel_info(), which was supposed to
replace it. They are completely different functions. Other plugins which
are likely to suffer from the same bug are:
  * pcm_file.c
  * pcm_plug.c

However, most other plugins used
pcm_plugin.c:snd_pcm_plugin_channel_info() before the "2005-01-20" patch.
It shares the same code with snd_pcm_generic_channel_info(). So this issue
raises a few question:
  * Is snd_pcm_generic_channel() as it is now valid? At least pcm_hooks
and likely pcm_file and pcm_plug don't work with it.
  * If it's valid, there is a necessity to create another generic
function, which clones the code previously provided by
snd_pcm_{hooks,file,plug}_channel_info() functions.

The attached patch solves the problem for me, but it is not an universal
solution. The patch should be applied against CVS as of 2005-01-21 or
later.

And now here it comes some other remarks regarding the "2005-01-20"
patch.
  * I guess, snd_pcm_plugin_fast_ops.status = snd_pcm_generic_status in
pcm_plugin.c is incorrect because it makes snd_pcm_plugin_status()
reduntant and these functions don't share the same code.
  * Plugins which haven't been "cleaned up" by the "2005-01-20" patch
include:
    - pcm_meter.c
    - pcm_null.c
    - pcm_share.c
    - pcm_shm.c
    The latter two seem to be kinda different beasts whereas the first two
shouldn't be too difficult to "_generic_"'ize.
======================================================================

----------------------------------------------------------------------
 modax - 04-03-05 17:53 
----------------------------------------------------------------------
I wonder where my alsa/os info has disappered. The bug applies to alsa-lib
1.0.8+cvs20050121 and later. I'm running Debian unstable and Linux kernel
2.6.11.5  with alsa-driver 1.0.9rc2+cvs20050330

Issue History
Date Modified  Username       Field                    Change              
======================================================================
04-03-05 17:42 modax          New Issue                                    
04-03-05 17:42 modax          File Added: hooks-channel-info-fix.diff           
        
04-03-05 17:53 modax          Note Added: 0004312                          
======================================================================




-------------------------------------------------------
SF email is sponsored by - The IT Product Guide
Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now.
http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click