Re: [PATCH] ALSA: control: confirm to return all identical information in 'activate' event data

[Takashi Iwai <tiwai@suse.de>]

At Tue, 10 Feb 2015 01:01:15 +0900,
Takashi Sakamoto wrote:
> 
> On Feb 10 2015 00:28, Takashi Iwai wrote:
> > At Tue, 10 Feb 2015 00:02:06 +0900,
> > Takashi Sakamoto wrote:
> >>
> >> When event originator doesn't set numerical ID in identical information,
> >> the event data includes no numerical ID, thus userspace applications
> >> cannot identify the control just by unique ID in event data.
> >>
> >> This commit fix this bug so as the event data includes all of identical
> >> information.
> >>
> >> Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
> >
> > You can't overwrite id pointer in this case.  It's a caller's object.
> 
> Exactly. I missed it...
> 
> > One way to fix would be to copy the id instance.  Another way would be
> > to change up/down_write() with _read(), and include snd_ctl_notify()
> > call with kctl->id inside the semaphore lock.
> >
> > The former would be less changes but consume the stack significantly.
> 
> If any sub-effects are allowed, we can use caller's data via the 
> pointer, like:
> memcpy(id, &kctl->id, sizeof(struct snd_ctl_elem_id);
> Then:
> snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_INFO, id);

That's what I suggested as the first example.


Takashi