global data via module howto

Roman Kurakin rik at
Mon Aug 21 11:00:50 UTC 2006

M. Warner Losh wrote:
> In message: <44E87CCD.30105 at>
>             Roman Kurakin <rik at> writes:
> :     I have the following problem:
> : module A
> :     int x;
> : 
> : module B
> :     extern int x;
> : 
> :     Module A is loaded, module B can't be loaded cause of unknow 'x'.
> : What should I do to make x global?
> Better to make module B depend on module A.  Making it global is
> generally a bad idea.
> in module A:
> In module B:
> MODULE_DEPEND(B, A, 1, 1, 1);
Module dependence is not the goal.
> Warner
> : PS. I am working on porting irda support for USB devices from NetBSD.
> : The current model consists of two layers hw and sw. hw is the usb device
> : driver. sw is some software layer the same for all device and it is a
> : child on top of hw 'bus'. To make this working I need to add
> : DRIVER_MODULE for each 'bus'. To make sw independent from the
> : bus I need to export _driver and _class structures and put DRIVER_MODULE
> : in 'bus' code instead of 'child'.
> Are you sure that you need to do this?  I'm pretty sure that you can
> create a base class irdabus and then derive all the hw modules that
> implement irdabus from than and all the children will automatically
> probe.  No need to export the driver/class structures.
I have a bit reversed case. In common case we have a driver for "bus" 
with many
consumers. And we have children that declares itself via DRIVER_MODULE.
If child could work on several buses it declares itself several times 
one for each
bus. In my case I have several drivers that could be treated as bus 
driver for the
same child:

 |            |           |
ustir       uirda     smth_else
 \            |           /

Imagine, if the network interface was implemented as a child of every 
adapter. This is the same. In common case I'll put DRIVER_MODULE in a child
for each bus and recompile after adding a new one. In this case I do no 
want to
recompile the child for every new "bus" since child do not depend on 
such "bus"
- it is the same for all. So we may call this a pseudo-device with 
unknown list
of buses. I know, I could implement this other way, but I just want to 
play with
newbus a bit and the original NetBSD driver was implemented this way.

> Warner
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