[asterisk-dev] RFC: DAHDI echo canceller configuration change

[Tzafrir Cohen]

On Thu, Jun 19, 2008 at 09:37:01PM +1200, Nic Bellamy wrote:
> Kevin P. Fleming wrote:
> > I'm working in a branch of DAHDI's 'linux' package:
> >
> > http://svn.digium.com/svn/dahdi/linux/team/kpfleming/modular_ec
> >
> > This branch contains modifications to allow one (or many) echo cancelers
> > to be built and loaded at the same time, and then runtime selection made
> > as to which one should be used on which channel(s). All of the existing
> > modules have been converted, and the core code is ready to use them, so
> > what I'm left with is deciding on a configuration method.
> >   
> [...]
> 
> I'm coming in a bit late here, but food for thought perhaps...
> 
> I'd actually done this ages ago for the Zaptel 1.2 branch, but never 
> found the time to update it for trunk in order to submit it. Too busy 
> using it ;-)
> 
> I did it somewhat differently though, in that I added an extra ioctl 
> called ZT_ECHOCANCELV2 that allowed you to specify the echo canceller 
> and other parameters.

Basically the path taken by the dynamic stuff.

> 
> With the corresponding patch to Asterisk, this allows settings the echo 
> canceller type on a per-channel basis in zapata.conf
> 
> The EC modules can be loaded/unloaded at will, as each keeps a use 
> count, however I kept one software EC built-in as a fail safe fall back.
> 
> I found this to be a decent "mechanism vs. policy" compromise - 
> mechanism in the kernel (Zaptel), policy in userspace (Asterisk).

Asterisk is not the only client of Zaptel . Even if the name DAHDI seems 
to imply so.

Specifically, I'm not sure how good it is that any userspace program
with a write access to a zaptel / dahdi device file can force loading
some kernel module . 

Where is it necessary for Asterisk to have write access to
/dev/{zap,dahdi}/ctl ?

-- 
               Tzafrir Cohen
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