[alsa-devel] snd_pcm_avail_update returns bogus values with the OSS PCM plugin

10 Jul 2009


      Hi.
For the attached test case snd_pcm_avail_update returns values higher  
than the buffer size when run with the OSS PCM plugin. Output of  
alsa-info.sh is at
http://www.alsa-project.org/db/?f=77a873e55d5d6ca50d67a035a9d6b7e10cca179d .
--- alsa_oss_pcm_avail_bug.c ---
/*
  * Public domain test case to illustrate a bug in the ALSA OSS PCM plugin
  * where snd_pcm_avail_update returns bogus values.
  */
#include <alsa/asoundlib.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
static short buf[803 * 2];
static snd_pcm_t *pcm_handle = NULL;
void close_pcm(void)
{
    if (pcm_handle)
    	snd_pcm_close(pcm_handle);
pcm_handle = NULL;
}
static int set_pcm_parameters(void) {
    snd_pcm_hw_params_t *hwparams;
    snd_pcm_hw_params_alloca(&hwparams);
if (snd_pcm_hw_params_any(pcm_handle, hwparams) < 0) {
    	fprintf(stderr, "snd_pcm_hw_params_any failed.\n");
    	return -1;
    }
if (snd_pcm_hw_params_set_access(pcm_handle, hwparams,
    			SND_PCM_ACCESS_RW_INTERLEAVED) < 0) {
    	fprintf(stderr, "snd_pcm_hw_params_set_access failed.\n");
    	return -1;
    }
if (snd_pcm_hw_params_set_format(pcm_handle, hwparams,
    			SND_PCM_FORMAT_S16) < 0) {
    	fprintf(stderr, "snd_pcm_hw_params_set_format failed.\n");
    	return -1;
    }
{
    	unsigned rate = 48000;
if (snd_pcm_hw_params_set_rate_near(pcm_handle, hwparams,
    				&rate, 0) < 0) {
    		fprintf(stderr, "snd_pcm_hw_params_set_rate_near failed.\n");
    		return -1;
    	}
    }
if (snd_pcm_hw_params_set_channels(pcm_handle, hwparams, 2) < 0) {
    	fprintf(stderr, "snd_pcm_hw_params_set_channels failed.\n");
    	return -1;
    }
{
    	unsigned ulatency = 100000;
if (snd_pcm_hw_params_set_buffer_time_near(pcm_handle,
    				hwparams, &ulatency, 0) < 0) {
    		fprintf(stderr, "snd_pcm_hw_params_set_buffer_time_near failed.\n");
    		return -1;
    	}
    }
if (snd_pcm_hw_params(pcm_handle, hwparams) < 0) {
    	fprintf(stderr, "snd_pcm_hw_params failed.\n");
    	return -1;
    }
{
    	snd_pcm_uframes_t bSize = 0;
if (snd_pcm_hw_params_get_buffer_size(hwparams, &bSize) < 0) {
    		fprintf(stderr, "snd_pcm_hw_params_get_buffer_size failed\n");
    		return -1;
    	}
printf("buffer_size: %u\n", (unsigned int) bSize);
    }
return 0;
}
static void test_loop(int n) {
    while (n--) {
    	snd_pcm_sframes_t sframes = snd_pcm_avail_update(pcm_handle);
    	printf("snd_pcm_avail: %d\n", (int) sframes);
    	printf("writing %d frames\n", (int) sizeof(buf) / 4);
    	sframes = snd_pcm_writei(pcm_handle, buf, sizeof(buf) / 4);
if (sframes != sizeof(buf) / 4) {
    		if (sframes < 0)
    			snd_pcm_prepare(pcm_handle);
printf("snd_pcm_writei returned %d\n", (int) sframes);
    	}
    }
}
int main(int argc, char **argv)
{
    atexit(close_pcm);
if (argc < 2) {
    	printf("usage: %s <ALSA pcm device>\n", argv[0]);
    	return 0;
    }
if (snd_pcm_open(&pcm_handle, argv[1],
    			SND_PCM_STREAM_PLAYBACK, 0) < 0) {
    	fprintf(stderr, "Error opening PCM device %s\n", argv[1]);
    	pcm_handle = NULL;
    	return -1;
    }
if (set_pcm_parameters() < 0)
    	return -1;
memset(buf, 0, sizeof(buf));
test_loop(500);
return 0;
}
--
Sindre Aamås