Bug#431724: Situation regarding mISDN

[Simon Richter]

Hi,

Tzafrir Cohen wrote:

>> Basically we need to get a list 
>> of all ISDN adapters (I guess the files in upstream's kernel package are 
>> going to be helpful there), and ask whether they want to use them with 
>> mISDN or I4L, then set up udev rules for that. 

> When exactly will this be done? modules are loaded at boot.

At install time.

> Note that qozap, zaphfc and vzaphfc from zaptel-modules also combat with 
> misdn in the fight to be the default for the device IDs.

Okay, so it may be a good idea to have some sort of framework where 
these could be integrated as well.

I think it would be a common configuration to have multiple HFC based 
cards in one box and run the TE side with zaphfc and the NT side with 
mISDN (that way, you get a zaptel timer for MoH and Meetme).

>> 4. Work with/against upstream to get a real init system working, which 
>> means teaching the kernel to defer loading the l1-3 drivers (this will, 
>> guess what, change the kernel<->userspace API/ABI again, but we can 
>> probably catch that in libmISDN). That was originally my plan for the 
>> CCCamp, but I was sick in bed during that time.

> What do you mean here?

The kernel immediately instantiates a device stack when the hardware 
module is loaded. This needs to be deferred until the device is actually 
used for the first time, because there is no hard dependency from the 
hardware modules to the l1-3 modules (they do not need any modules), and 
the stack setup even succeeds if these modules are not loaded, but we 
end up with a few NULL pointers in kernelspace that are dereferenced on 
behalf of asterisk later.

> Do you mean that every non-blacklisted module will get the hardware
> before your module?

That is undefined, but pretty likely, given that we have to load 5 
modules while i4l only loads two or three AFAIK. Some testing without 
the additional dependencies showed that it was a matter of luck 
actually, mISDN won 1/3 of the times, i4l 2/3; I expect that to shift in 
favour of I4L.

    Simon