And symbol versioning doesn't even guarantee compatibility. It catches only a small subset of the kinds of changes in the definition of a function that can make it not backward compatible. If the way register_chrdev interprets one of its parameters changes in a non-backward-compatible way, its version suffix won't change -- the parameter still has the same C type.
And there's no way an option like -f on insmod can get around this.
So it is generally not wise to use symbol versioning.
Of course, if you have a base kernel that was compiled with symbol versioning, then you must have all your LKMs compiled likewise, and vice versa. Otherwise, you're guaranteed to get those "unresolved symbol reference" errors.
