[driver-discuss] Is it possible for two drivers to depend on each other?

[Freeman.Liu at Sun.COM]

Thanks for all your help.

BRs
  --Freeman

Bart Smaalders wrote:

> Freeman.Liu at sun.com wrote:
>
>> Bart Smaalders wrote:
>>
>>> LiuFeng wrote:
>>>
>>>> Good day, everyone!
>>>>
>>>> I have a question here.
>>>> I have two drivers, say A and B, that cooperate to provide a 
>>>> specific funcationality. A can call a routine provided by B and 
>>>> passes in a callback as a parameter so that B can use that to call 
>>>> into A. From this point of view, they behavior like module. Such 
>>>> calls could be issued even before the drivers create minor nodes. 
>>>> Yet I can only create one-way dependency, say A depends on B. The 
>>>> issues is: it's possible that A could be unloaded, which is very 
>>>> possible with debug kernel, when B call into A. And the system will 
>>>> panic.
>>>>
>>>
>>> Before handing out a function pointer for callback, you need
>>> to make sure your module cannot be unloaded until the callback
>>> is explicitly disabled....
>>
>>
>> Yes, could you explain more about how to make it sure ?
>
>
> http://developers.sun.com/solaris/developer/support/driver/faqs.html#QA3.28 
>
>
> 3.28  Under certain conditions on the Solaris OS, a device driver 
> cannot be unloaded. What are those conditions?
>
>     * If a driver has no detach routine (nodev is specified in the 
> driver's dev_ops(9S) for its detach routine).
>     * If EBUSY is returned from the driver's _fini() routine.
>     * If the driver has a positive number of references to it.
>     * If the driver has a bus_ops structure specified in its dev_ops 
> structure, and it has children attached to it (therefore it is a nexus 
> driver).
>     * If the driver has no dev_ops at all!
>
>
> So if your detach routine returns DDI_FAILURE rather than
> DDI_SUCCESS, you can prevent your module from unloading...
>
> For an example see:
>
> http://cvs.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/io/devpool.c#pool_detach 
>
>
>
> - Bart
>