Avoiding global variables in kernel modules
 

HI

I have two modules A and B in the kernel which i am trying to hack by introducing a variable in A which is of type 'extern' (and using EXPORT_SYMBOL) and then calling it in B.

Now the problem is how to introduce that variable in module A. Currently i have made a global variable and it works fine but global variable in kernel is a bad bad thing.

I tried having an 'extern' function in A which have that variable and calling that function in module B, but then again how would module A use my variable unless the variable is available outside the scope of that function and that again means a global variable.

Any idea on this avoiding of global variables in Kernel programming.

thx
cheers

Depends on what exactly you're trying to achieve. I don't know the semantics of your variable, but I assume it's somehow "bound" to one of the modules, so let's say it's semantically bound to module A.

Then, the best way would be to make it local to module A and introduce a public interface for other modules to use that provides "valid" operations on the variable. B would call these functions instead of accessing the variable directly. This way, it's also clear which module depends on the other (B on A).

Why do you think so ? Hint: think about (nested) scopes and data exchange between them.

Indeed, if the variable's purpose is data exchange, there's nothing wrong with a global variable -- but, that's a design decision that can't be generally answered without some semantic knowledge.