In ALSA control core, when several events occurs for an element, they're
represented bit mask (struct snd_ctl_event.data.elem.mask). Thus userspace
applications can handles these events separately in one I/O operation.
There's an exception; removal event. This is represented by all of bits in
the mask. Therefore, when a removal event occurs for an element, all of
queued events for the element are overwritten.
This works worse for a combination of applications which add/remove control
elements and applications which keep a cache of elements. For example,
let's assume a case that:
1.some elements are added by ioctl(SNDRV_CTL_IOCTL_ELEM_ADD).
2.ALSA control core handles the request and queues 'add' event.
3.applications don't read the event yet.
4.the elements are removed by ioctl(SNDRV_CTL_IOCTL_ELEM_REMOVE)
5.ALSA control core handles the request and queues 'removal' event by
overwriting queued events.
6.applications read the event at last.
7.the applications cannot find removed elements in their cache data.
Especially, when applications use hctl interface of ALSA userspace library,
this situation occurs because the interface is designed to keep element
cache implicitly inner the library. PulseAudio is such an application. When
executing a test program of ALSA library (test/user-ctl-element-set.c),
pulseaudio process aborts due to assertion at calls of
snd_hctl_handle_events().
The rule to represent events is in ALSA kernel/userspace interfaces
(UAPI header) and it's difficult to improve the rule. Therefore,
developers should pay enough attention to the fact that userspace
applications can receive removal events for elements which are not
notified with 'add' event.
For this reason, this commit removes assertion from event handler of ALSA
hctl API.
CC: pulseaudio-discuss@lists.freedesktop.org
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Upon an interrupt, it is necessary to abort the wait loops with the EINTR
error code. Introduce snd_*_abort() functions to handle this case.
Signed-off-by: Jaroslav Kysela <perex@perex.cz>
The case where the element is unavailable (for example gone away since
the event was created) is handled beneath.
See also bug 5471.
https://bugtrack.alsa-project.org/alsa-bug/view.php?id=5471
Signed-off-by: Takashi Iwai <tiwai@suse.de>
In case when kcontrol differs only by device or subdevice numbers, the
find function can give wrong results.
Signed-off-by: Jaroslav Kysela <perex@perex.cz>
This makes it possible to write them to .data.rel.ro or to .rodata if
there is no relocation involved (arrays of character arrays).
Signed-off-by: Diego E. 'Flameeyes' Pettenò <flameeyes@gmail.com>
snd_hctl_wait() currently makes a lot of assumptions that fall outside
the defined API. snd_pcm_wait(), however, follows the API nicely so the
new version is based on that.
Signed-off-by: Pierre Ossman <ossman@cendio.se>
ordinary mixer:
- revised Ordinary Mixer I/O type
- sndo_mixer_open() take PCMs rather than strings to pass
the real relationship
- an initial version of toplevel alisp script
more alisp development:
- renamed a* functions to A* functions (acall -> Acall etc.)
- many improvements (unset*, exfun, Acall pcm_info, Asnderr, Asyserr)
