Re: [PATCH 2/2] ALSA: pcm: auto-fill buffer with silence when draining playback

[Takashi Iwai <tiwai@suse.de>]

On Thu, 13 Apr 2023 13:10:34 +0200,
Oswald Buddenhagen wrote:
> 
> On Thu, Apr 13, 2023 at 12:28:34PM +0200, Takashi Iwai wrote:
> > On Thu, 13 Apr 2023 12:16:04 +0200, Oswald Buddenhagen wrote:
> >> On Thu, Apr 13, 2023 at 07:42:06AM +0200, Takashi Iwai wrote:
> >> > Also, we may skip the
> >> > workaround for applications accessing directly via mmap as default.
> >> > no, because one may easily miss that more than one period is
> >> required.
> >> also, i think that forgetting it entirely is an easy mistake to make,
> >> even if it's harder with mmap than with write.
> > 
> > I don't agree with that point -- if application wants the access only
> > via mmap (without any write actions via alsa-lib functions), the
> > buffer and data management relies fully on the application itself.
> > Manipulating the data *silently* is no good action for such
> > applications.
> 
> > For them, the drain simply means to stop at the certain point.
> > 
> i don't think that's true. if an app wants to control things finely,
> it would just use start/stop and manage the timing itself. draining
> otoh is a convenient fire-and-forget operation. that makes it easy to
> miss the finer details, which is why i'm so insistent that it should
> just work out of the box.

Sure, but that's still no excuse to ignore the possibility blindly.

> if you exclude mmapped devices in kernel, you exclude plughw with
> emulated write(), so you'd have to add yet more code to compensate for
> that.

No, I wrote "if application wants the access only via mmap (without
any write actions via alsa-lib functions)".  So if application writes
via plugin write(), we should apply the workaround, too.

> and doing it all in user space is yet more code. for all i can
> tell, it's really just layers of complexity to solve a non-problem.

I don't get it: we're talking about the sw_params call in alsa-lib's
drain function, and how can it be *so* complex...?


Takashi