snd_pcm_ops函数的作用.doc,我们从上章知道,用户对设备节点进行操作,最终会调用到/sound/core/pcm_native.c里面的snd_pcm_f_ops[2]所指的函数。 const struct file_operations snd_pcm_f_ops[2] = { { .owner = THIS_MODULE, .write = snd_pcm_write, .aio_write = snd_pc
snd_pcm_f_ops会通过一些处理后最终会调用我们的structsnd_pcm_ops结构体所指的函数,因为/sound/core/pcm_native.c的代码比较繁琐和复杂而且大部分都是不需要进行修改的了,我们这里就不对其进行分析了,我们这次主要分析的对像是structsnd_pcm_ops结构体所指向的函数,这结构体所指的函数与我们的驱动程序息息相关。
一,虚拟机内部声音导出到本地宿主机内 主要是针对qemu虚拟机下的音频如何使用,首先要查看help命令: AI检测代码解析 qemu-system-x86_64 -audio-help 1. 这个命令能告诉我们audio的一些基本的信息和使用方法,以及Qemu支持的驱动 AI检测代码解析 Audio options: QEMU_AUDIO_DAC_FIXED_SETTINGS: boolean, default = 1...
snd_pcm_dev_register snd_register_device_for_dev 创建"pcmC%iD%ip"或者"pcmC%iD%ic"设备节点,它的fops为snd_pcm_f_ops[2] snd_pcm_f_ops[2] ==> snd_pcm_playback_open或者snd_pcm_capture_open ==> snd_pcm_open或者oss的snd_pcm_oss_f_reg.snd_pcm_oss_open,这就对应/dev/dsp了 ==> ...
snd_pcm_f_ops[2] ==> snd_pcm_playback_open或者snd_pcm_capture_open ==> snd_pcm_open或者oss的snd_pcm_oss_f_reg.snd_pcm_oss_open,这就对应/dev/dsp了 ==> snd_pcm_open_file或者oss的snd_pcm_oss_open_file ==> snd_pcm_open_substream ...
snd_pcm_f_ops[2] ==> snd_pcm_playback_open或者snd_pcm_capture_open ==> snd_pcm_open或者oss的snd_pcm_oss_f_reg.snd_pcm_oss_open,这就对应/dev/dsp了 ==> snd_pcm_open_file或者oss的snd_pcm_oss_open_file ==> snd_pcm_open_substream ...
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ctl->ops = &snd_ctl_hw_ops; ctl->private_data = hw; ctl->poll_fd = fd; *handle = ctl; filename等于"/dev/snd/pcmC0D0p" ==> fd = snd_open_device(filename, fmode); ==> return snd_pcm_hw_open_fd(pcmp, name, fd, 0, sync_ptr_ioctl); ...
_snd_pcm_writei会调用pcm->fast_ops->writei进行实际操作。查看aplay.c源码始终没有发现PCM设备中的结构体const snd_pcm_fast_ops_t *fast_ops在哪里初始化,极大可能在snd_pcm_open中进行了相应的操作。snd_pcm_open 具体分析alsa_utils aplay.c 中调用 snd_pcm_open 如下 ... char *pcm_name = "...
filename等于"/dev/snd/pcmC0D0p" ==> fd = snd_open_device(filename, fmode); ==> return snd_pcm_hw_open_fd(pcmp, name, fd, 0, sync_ptr_ioctl); ==> snd_pcm_new(&pcm, SND_PCM_TYPE_HW, name, info.stream, mode); pcm->ops = &snd_pcm_hw_ops; pcm->fast_ops = &snd_...