Re: Persistent module storage [was Linux 2.4 Status / TODO page]

Martin Dalecki
2000-11-06T14:22:28Z

David Woodhouse wrote:
>
> jgarzik@mandrakesoft.com said:
> > * Driver initializes mixer to 100% muted * Userspace app sets desired
> > values to /dev/mixer * Userspace app opens /dev/dsp to play sound
>
> > I don't see where any sound can "escape" in this scenario, and it
> > doesn't require any module data persistence...
>
> * User boots kernel
> * User loads mixer app
> * Sound module is autoloaded, defaults to zero levels. This is fine.
> * User sets 'line in' level to appropriate level to listen to radio
> * User closes mixer app
> * Time passes
> * Sound module is unloaded
> * User continues to happily listen to radio through sound card
> * Time passes
> * User is listening intently to something on the radio
> * Something wants to beep through /dev/audio
> * Sound module is autoloaded again, default to zero levels.
> This time it is _NOT_ fine. User is rightly pissed off :)
>
> It's fine to default to zero levels the first time the sound module is
> loaded after booting. Not on subsequent reloads though.
>
> A long time ago, I made the sb16 driver use the persistent storage facility
> of kerneld to store mixer levels. I was happy with this right up until
> kerneld disappeared :)

It was removed for good reasons.

> I then made a version which read the current mixer levels back from the
> hardware on initialisation, and didn't reset them. That didn't work on all
> sb16 hardware, but it worked for me (tm).
>
> Persistent storage is the best way to do it though. It doesn't have to be
> persistent over reboots, just during the lifetime of the kernel.

No! The best way to do it are just *persistently loaded* modules.
It's THAT simple!