alsa-project/alsa-lib issue #137 was opened from MHoyer12345678:
Playing sound using snd_pcm_writei in a dmix setup might result in an infinite loop when sound card is removed.
**Setup:**
- dmix setup - pcm dmix device opened non blocking - snd_pcm_writei used with poll (POLLERR is not evaluated)
**Trigger:** - usb sound card is removed (e.g. by "echo 0 > /sys/bus/usb/x-x/authorized")
**Observation:** - snd_pcm_writei returns -EAGAIN on each call - snd_pcm_state report state RUNNING
**Expected:** - snd_pcm_writei returns -ENODEV (as happening in case a pure hw configuration is used without dmix plugin) - snd_pcm_state report state DISCONNECTED (as happening in case a pure hw configuration is used without dmix plugin)
**Root Cause:** - snd_pcm_writei calls snd_pcm_write_areas - snd_pcm_write_areas requests state of dmix pcm device (state = __snd_pcm_state(pcm);) - dmix implementation of snd_pcm_state requests state from slave hw device (state = snd_pcm_state(dmix->spcm);) - hw implementation of snd_pcm_state executes an ioctl (query_status -> sync_ptr1) - the ioctl call fails with -ENODEV (after the device has been removed) - pcm_hw returns -ENODEV as state - dmix implementation of snd_pcm_state ends in default section of the switch block - this leads to the unchanged dmix->state returned - this way, the -ENODEV from the slave device is finally ignored in dmix plugin
**Potential Fix:** - Add the following three lines to snd_pcm_hw_state in pcm_hw.c after query_status_data
``` //disconnected HW is reported via a failed IOCTL return -ENODEV if (err == -ENODEV) return SND_PCM_STATE_DISCONNECTED; ``` - The fix takes -ENODEV as trigger to return state DISCONNECTED
Hope this helps ...
Issue URL : https://github.com/alsa-project/alsa-lib/issues/137 Repository URL: https://github.com/alsa-project/alsa-lib