Dmix plugin does not update state when sound card is removed.

[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 ...

[perexg]

Thank you for the analysis. Fix is in the above commit.