[alsa-devel] [PATCH][RFC][alsa-utils 0/9] alsactl: monitor mode friendly for

[Takashi Sakamoto]

Hi,

A command of 'alsactl' has 'monitor' mode to print events emitted by
observed control nodes. This mode is not friendly for plug-and-play
devices.

A bug is reported that the mode consumes 100% of CPU time when
detecting disconnection of observed sound card[1]. A process of
alsactl doesn't release ALSA control character device at disconnection.
This is quite bad in a view of system.

Furthermore, this mode cannot handle control nodes for newly-detected
sound card.

This patchset is my attempt to improve the mode to handle
disconnection of observed sound card and new detection of sound card.

A rough summary of this patchset:
 - maintains observed control nodes by link-list
 - uses epoll(7) instead of poll(2) to avoid following the list every time
   of poll loop, 
 - control node for disconnected sound card is not observed anymore and
   dropped from the list.
 - the list is rescan and observation is updated when detecting new
   sound card. Linux-specific inotify(7) is used for this purpose.

I'm happy if receiving test reports and indication of new bugs.

[1] [alsa-devel] alsactl monitor spins at 100% cpu after unplugging USB headphones
http://mailman.alsa-project.org/pipermail/alsa-devel/2018-September/140580.html

Takashi Sakamoto (9):
  alsactl: install signal handler
  alsactl: split event loop code to a function
  alsactl: add an iterator of registered instances of sound card
  alsactl: use epoll(7) instead of poll(2)
  alsactl: use link list to maintain source of events
  alsactl: use a list of source for event dispatcher instead of an array
    of source
  alsactl: obsolete array for maintenance of handlers
  alsactl: handle disconnection of sound card
  alsactl: handle detection of new sound card

 alsactl/monitor.c | 403 ++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 356 insertions(+), 47 deletions(-)

-- 
2.19.0