Description of problem:
Attempting to rmmod something that's not actually built as a module now gives a slightly confusing error:

# rmmod loop
libkmod: kmod_module_get_holders: could not open '/sys/module/loop/holders': No such file or directory
Error: Module loop is in use

Previously rmmod from module-init-tools gave a still vague but better "not found" message:

# rmmod ext2
ERROR: Module ext2 does not exist in /proc/modules

Version-Release number of selected component (if applicable):
kmod-*

How reproducible:
100%

Steps to Reproduce:
1. compile something that can be built as a module as a built-in 
2. rmmod $thing


Actual results:
# rmmod loop
libkmod: kmod_module_get_holders: could not open '/sys/module/loop/holders': No such file or directory
Error: Module loop is in use

Which isn't really true: it's not in use, it's simply built in to vmlinuz so unloading makes no sense.

Expected results:
modprobe does the right thing:

# modprobe -r loop
FATAL: Module loop is builtin.


Additional info:
I know rmmod is the low-level tool and users should be using modprobe -r (or just not messing with this in the first place.. :) but knowledge of modprobe to load and rmmod to unload seems much more widespread among admins and the current behaviour looks at first like a kernel bug (if you didn't realise that there are paths directories missing in /sys/modules/$thing and the module name isn't present in /proc/modules you might think some refcount was broken etc.).