On Sun, 10 Jul 2016 17:12:34 +0200, Takashi Sakamoto wrote: > > 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@xxxxxxxxxxxxxxxxxxxxx > Signed-off-by: Takashi Sakamoto <o-takashi@xxxxxxxxxxxxx> Applied, thanks. Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
