pass kernel pointers to the sysctl ->proc_handler method v2

From: Christoph Hellwig
Date: Tue Apr 21 2020 - 13:15:46 EST


Hi all,

this series changes the sysctl ->proc_handler methods to take kernel
pointers. This simplifies some of the pointer handling in the methods
(which could probably be further simplified now), and gets rid of the
set_fs address space overrides used by bpf.

Changes since v1:
- drop a patch merged by Greg
- don't copy data out on a write
- fix buffer allocation in bpf