bug in alsa use.

[dengxf@…]

function SetParameters? in audiooutputalsa.cpp, there is a wrong usage of alsa api. snd_pcm_hw_params_get_buffer_size or snd_pcm_hw_params_get_period_size should be called after snd_pcm_hw_params. if it is called before snd_pcm_hw_params, they maybe failed. for example: call snd_pcm_hw_params_set_rate_near with 12000, when call snd_pcm_hw_params_get_buffer_size, it will failed.

here is a patch: --- audiooutputalsa.cpp.orig 2010-04-01 20:09:31.000000000 +0800 +++ audiooutputalsa.cpp 2010-04-01 20:09:59.000000000 +0800 @@ -421,16 +421,6 @@

return err;

}

• if ((err = snd_pcm_hw_params_get_buffer_size(params, &buffer_size)) < 0)
• {
• Error(QString("Unable to get buffer size for playback: %1")
• .arg(snd_strerror(err)));
• return err;
• } else {
• VERBOSE(VB_AUDIO, QString("get_buffer_size returned %1").arg(buffer_size));
• }
• soundcard_buffer_size = buffer_size * audio_bytes_per_sample;

-

/* set the period time */ if ((err = snd_pcm_hw_params_set_period_time_near(

handle, params, &period_time, &dir)) < 0)

@@ -442,20 +432,30 @@

VERBOSE(VB_AUDIO, QString("set_period_time_near returned %1").arg(period_time));

}

• if ((err = snd_pcm_hw_params_get_period_size(params, &period_size,
• &dir)) < 0) {
• Error(QString("Unable to get period size for playback: %1")

+ /* write the parameters to device */ + if ((err = snd_pcm_hw_params(handle, params)) < 0) { + Error(QString("Unable to set hw params for playback: %1") + .arg(snd_strerror(err))); + return err; + } + + if ((err = snd_pcm_hw_params_get_buffer_size(params, &buffer_size)) < 0) + { + Error(QString("Unable to get buffer size for playback: %1")

.arg(snd_strerror(err)));

return err;

} else {

• VERBOSE(VB_AUDIO, QString("get_period_size returned %1").arg(period_size));

+ VERBOSE(VB_AUDIO, QString("get_buffer_size returned %1").arg(buffer_size));

}

+ soundcard_buffer_size = buffer_size * audio_bytes_per_sample;

• /* write the parameters to device */
• if ((err = snd_pcm_hw_params(handle, params)) < 0) {
• Error(QString("Unable to set hw params for playback: %1")

+ if ((err = snd_pcm_hw_params_get_period_size(params, &period_size, + &dir)) < 0) { + Error(QString("Unable to get period size for playback: %1")

.arg(snd_strerror(err)));

return err;

+ } else { + VERBOSE(VB_AUDIO, QString("get_period_size returned %1").arg(period_size));

}

/* get the current swparams */

[tarek-spam@…]

patch

[tarek-spam@…]

I've attached a patch file because the above was mangled

[JYA]

Fixed since merge of hd-audio branch

[JYA]

Some more information following questions on IRC. The ALSA code this patch was modifying doesn't exist anymore. Most of the code in ALSA was fully rewritten.

The patch attached in the ticket wasn't used.