[$] Making life (even) harder for proprietary modules

The kernel community has never had a smooth relationship with the purveyorsof proprietary kernel modules. Developers tend to strongly dislike thosemodules, which cannot be debugged or fixed by anybody other than theircreator, and many see them as a violation of the kernel's license and theircopyrights on the code. Nonetheless, proprietary modules are tolerated,within bounds. A recent patch from Christoph Hellwig suggests that thosebounds are about to be tightened slightly, in a somewhat surprising way.