alsa声卡分析alsa-utils调用过程
如何分析tinyplay 播放音频和tinymix的过程?需要相应的工具来支持追查;
一、分析tinyplay和tinymix:
1.1 利用strace工具:
strace -o tinyplay.log tinyplay 1.wav
strace -o tinymixer.log tinymixer "SEC_MI2S_RX Audio Mixer MultiMedia1" 1
利用strace工具获取APP的log,从应用层往下看;
1.2 分析alsa-utils源码:
tiny工具源码在android/external/tinyalsa目录下;
二、tinyplay调用分析(tinyplay.log搜索设备节点“/dev/snd/pcmC0D0p”)
2.1 tinyplay的open过程:
snd_pcm_f_ops[0]是播放音频的file_operations,snd_pcm_f_ops[1]则是录音的file_operations:
- const struct file_operations snd_pcm_f_ops[] = {
- {
- .owner = THIS_MODULE,
- .write = snd_pcm_write,
- .aio_write = snd_pcm_aio_write,
- .open = snd_pcm_playback_open,
- .release = snd_pcm_release,
- .llseek = no_llseek,
- .poll = snd_pcm_playback_poll,
- .unlocked_ioctl = snd_pcm_playback_ioctl,
- .compat_ioctl = snd_pcm_ioctl_compat,
- .mmap = snd_pcm_mmap,
- .fasync = snd_pcm_fasync,
- .get_unmapped_area = snd_pcm_get_unmapped_area,
- },
- {
- .owner = THIS_MODULE,
- .read = snd_pcm_read,
- .aio_read = snd_pcm_aio_read,
- .open = snd_pcm_capture_open,
- .release = snd_pcm_release,
- .llseek = no_llseek,
- .poll = snd_pcm_capture_poll,
- .unlocked_ioctl = snd_pcm_capture_ioctl,
- .compat_ioctl = snd_pcm_ioctl_compat,
- .mmap = snd_pcm_mmap,
- .fasync = snd_pcm_fasync,
- .get_unmapped_area = snd_pcm_get_unmapped_area,
- }
- };
我们从snd_pcm_playback_open函数开始向下分析:
- static int snd_pcm_playback_open(struct inode *inode, struct file *file)
- {
- struct snd_pcm *pcm;
- int err = nonseekable_open(inode, file);
- if (err < )
- return err;
- pcm = snd_lookup_minor_data(iminor(inode),
- SNDRV_DEVICE_TYPE_PCM_PLAYBACK); //取得其私有数据并返回的
- err = snd_pcm_open(file, pcm, SNDRV_PCM_STREAM_PLAYBACK);
- if (pcm)
- snd_card_unref(pcm->card); //减少设备对象的引用计数 snd_card_unref(card);
- return err;
- }
在下面调用了snd_pcm_open函数:
- static int snd_pcm_open(struct file *file, struct snd_pcm *pcm, int stream)
- {
- int err;
- wait_queue_t wait;
- if (pcm == NULL) {
- err = -ENODEV;
- goto __error1;
- }
- err = snd_card_file_add(pcm->card, file);
- if (err < )
- goto __error1;
- if (!try_module_get(pcm->card->module)) {
- err = -EFAULT;
- goto __error2;
- }
- init_waitqueue_entry(&wait, current);
- add_wait_queue(&pcm->open_wait, &wait);
- mutex_lock(&pcm->open_mutex);
- while () {
- err = snd_pcm_open_file(file, pcm, stream); // 将操作该声卡card的应用程序添加到card->files_list
- if (err >= )
- break;
- if (err == -EAGAIN) {
- if (file->f_flags & O_NONBLOCK) {
- err = -EBUSY;
- break;
- }
- } else
- break;
- set_current_state(TASK_INTERRUPTIBLE);
- mutex_unlock(&pcm->open_mutex);
- schedule();
- mutex_lock(&pcm->open_mutex);
- if (pcm->card->shutdown) {
- err = -ENODEV;
- break;
- }
- if (signal_pending(current)) {
- err = -ERESTARTSYS;
- break;
- }
- }
- remove_wait_queue(&pcm->open_wait, &wait);
- mutex_unlock(&pcm->open_mutex);
- if (err < )
- goto __error;
- return err;
- __error:
- module_put(pcm->card->module);
- __error2:
- snd_card_file_remove(pcm->card, file);
- __error1:
- return err;
- }
再从snd_pcm_open_file继续向下看:
- static int snd_pcm_open_file(struct file *file,
- struct snd_pcm *pcm,
- int stream)
- {
- struct snd_pcm_file *pcm_file;
- struct snd_pcm_substream *substream;
- int err;
- err = snd_pcm_open_substream(pcm, stream, file, &substream); //打开substream结构体
- if (err < )
- return err;
- pcm_file = kzalloc(sizeof(*pcm_file), GFP_KERNEL);
- if (pcm_file == NULL) {
- snd_pcm_release_substream(substream);
- return -ENOMEM;
- }
- pcm_file->substream = substream;
- if (substream->ref_count == ) {
- substream->file = pcm_file;
- substream->pcm_release = pcm_release_private;
- }
- file->private_data = pcm_file;
- return ;
- }
- int snd_pcm_open_substream(struct snd_pcm *pcm, int stream,
- struct file *file,
- struct snd_pcm_substream **rsubstream)
- {
- struct snd_pcm_substream *substream;
- int err;
- err = snd_pcm_attach_substream(pcm, stream, file, &substream);
- if (err < )
- return err;
- if (substream->ref_count > ) {
- *rsubstream = substream;
- return ;
- }
- err = snd_pcm_hw_constraints_init(substream); //初始化substream结构体
- if (err < ) {
- snd_printd("snd_pcm_hw_constraints_init failed\n");
- goto error;
- }
- if ((err = substream->ops->open(substream)) < )
- goto error;
- substream->hw_opened = ;
- err = snd_pcm_hw_constraints_complete(substream);
- if (err < ) {
- snd_printd("snd_pcm_hw_constraints_complete failed\n");
- goto error;
- }
- *rsubstream = substream;
- return ;
- error:
- snd_pcm_release_substream(substream);
- return err;
- }
snd_pcm_open_substream
在snd_pcm_open_substream函数中:
- if ((err = substream->ops->open(substream)) < ) // substream->ops : snd_pcm_ops结构体
- goto error;
依次调用cpu_dai, dma, codec_dai, machine(三大模块)的open或startup函数;
msm_mi2s_snd_startup函数:
- struct snd_soc_pcm_runtime *rtd = substream->private_data;
- struct snd_soc_card *card = rtd->card;
- struct snd_soc_dai *cpu_dai = rtd->cpu_dai;
- struct snd_soc_codec *codec = rtd->codec;
设置snd_soc_pcm_runtime的cpu、codec等模块;然后在snd_soc_pcm_runtime函数中对codec函数进行相应的设置,之后通过音频数据流通道播放出声音;
调用过程如下图:
2.2 tinyplay的ioctl过程:
同样也是snd_pcm_f_ops[0]结构体的file_operations:
- {
- .owner = THIS_MODULE,
- .write = snd_pcm_write,
- .aio_write = snd_pcm_aio_write,
- .open = snd_pcm_playback_open,
- .release = snd_pcm_release,
- .llseek = no_llseek,
- .poll = snd_pcm_playback_poll,
- .unlocked_ioctl = snd_pcm_playback_ioctl,
- .compat_ioctl = snd_pcm_ioctl_compat,
- .mmap = snd_pcm_mmap,
- .fasync = snd_pcm_fasync,
- .get_unmapped_area = snd_pcm_get_unmapped_area,
- },
从snd_pcm_playback_ioctl函数向下看:
- static long snd_pcm_playback_ioctl(struct file *file, unsigned int cmd,
- unsigned long arg)
- {
- struct snd_pcm_file *pcm_file;
- pcm_file = file->private_data; //获取相应的私有数据
- if ((((cmd >> ) & 0xff) != 'A') && (((cmd >> ) & 0xff) != 'C'))
- return -ENOTTY;
- return snd_pcm_playback_ioctl1(file, pcm_file->substream, cmd,
- (void __user *)arg);
- }
snd_pcm_playback_ioctl1:
- static int snd_pcm_playback_ioctl1(struct file *file,
- struct snd_pcm_substream *substream,
- unsigned int cmd, void __user *arg)
- {
- if (snd_BUG_ON(!substream))
- return -ENXIO;
- if (snd_BUG_ON(substream->stream != SNDRV_PCM_STREAM_PLAYBACK))
- return -EINVAL;
- //根据case不同,对播放进行相应的不同操作
- switch (cmd) {
- case SNDRV_PCM_IOCTL_WRITEI_FRAMES:
- {
- struct snd_xferi xferi;
- struct snd_xferi __user *_xferi = arg;
- struct snd_pcm_runtime *runtime = substream->runtime;
- snd_pcm_sframes_t result;
- if (runtime->status->state == SNDRV_PCM_STATE_OPEN)
- return -EBADFD;
- if (put_user(, &_xferi->result))
- return -EFAULT;
- if (copy_from_user(&xferi, _xferi, sizeof(xferi)))
- return -EFAULT;
- result = snd_pcm_lib_write(substream, xferi.buf, xferi.frames);
- __put_user(result, &_xferi->result);
- return result < ? result : ;
- }
- case SNDRV_PCM_IOCTL_WRITEN_FRAMES:
- {
- struct snd_xfern xfern;
- struct snd_xfern __user *_xfern = arg;
- struct snd_pcm_runtime *runtime = substream->runtime;
- void __user **bufs;
- snd_pcm_sframes_t result;
- if (runtime->status->state == SNDRV_PCM_STATE_OPEN)
- return -EBADFD;
- if (runtime->channels > )
- return -EINVAL;
- if (put_user(, &_xfern->result))
- return -EFAULT;
- if (copy_from_user(&xfern, _xfern, sizeof(xfern)))
- return -EFAULT;
- bufs = memdup_user(xfern.bufs,
- sizeof(void *) * runtime->channels);
- if (IS_ERR(bufs))
- return PTR_ERR(bufs);
- result = snd_pcm_lib_writev(substream, bufs, xfern.frames);
- kfree(bufs);
- __put_user(result, &_xfern->result);
- return result < ? result : ;
- }
- case SNDRV_PCM_IOCTL_REWIND:
- {
- snd_pcm_uframes_t frames;
- snd_pcm_uframes_t __user *_frames = arg;
- snd_pcm_sframes_t result;
- if (get_user(frames, _frames))
- return -EFAULT;
- if (put_user(, _frames))
- return -EFAULT;
- result = snd_pcm_playback_rewind(substream, frames);
- __put_user(result, _frames);
- return result < ? result : ;
- }
- case SNDRV_PCM_IOCTL_FORWARD:
- {
- snd_pcm_uframes_t frames;
- snd_pcm_uframes_t __user *_frames = arg;
- snd_pcm_sframes_t result;
- if (get_user(frames, _frames))
- return -EFAULT;
- if (put_user(, _frames))
- return -EFAULT;
- result = snd_pcm_playback_forward(substream, frames);
- __put_user(result, _frames);
- return result < ? result : ;
- }
- }
- return snd_pcm_common_ioctl1(file, substream, cmd, arg);
- }
从snd_pcm_common_ioctl1继续分析,进入函数的prepare中:
当函数prepare完毕后,就一切准备就绪了,只等一个trigger;而trigger的执行会在上层的alsalib调用write的函数触发;prepare过程可以看下图,具体就不继续分析了:
下一节我们将来分析tinymixer的调用过程;
alsa声卡分析alsa-utils调用过程(二)-tinymixer
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