CONFIG_* used by user-space to figure out whether a feature is on/off

Konrad Rzeszutek Wilk
2013-07-15T15:40:56Z

Hey Linus,

I am hoping you can help me draw an understanding and a line in sand whether:
a) Tools should not depend on /proc/config.gz to figure out whether
a kernel has some CONFIG_X=y feature.

b) If they are OK to do so, what do we do when certain CONFIG_X options
get reworked/removed. Would they be considered regressions? Aka
is this similar to 'you shall not break user-space'?

Irrespective of that, do you have any ideas of how a user-space program (say GRUB)
can figure out whether the configuration stanze it generates is supported by
the kernel. If you don't want to answer this question - since this might
open a can of worms you prefer not to deal with - that is absolutly OK.

Folks have been tossing ideas such as:
- Let the user deal with it and if it does not boot - oh well.
- readelf or objdump.
- use /boot/config-<kernel>-<version> as most (all?) distros stick that in
there.

Thanks!