passing 'config' file data to a kernel loadable module ??

[John Baldwin]

On 12/30/14 4:13 PM, Robert Bonomi wrote:
> 
> I'm hacking on an existing screen-saver module, and would like to set options
> in the config file that are passed to the compiler when the module is built.
> 
> I can't find a decent description of the gory details of HOW 'config' works.
> Chapter 2 of the SMM, "Building 4.4BSD Kernels with Config" has falsehoods --
>   to wit: the example on page 10, under the 'options' keyword, given as
>        'options -DFUNNY,-DHAHA'
>   causes 'config' to abort with a fatal error.
> Apparently an 'option' must be defined 'somewhere else', before config
> recognizes it. <wry grin>

Yes, in sys/conf/options*.

> I've got an 'ugly' method -- "makeoptions CONF_CLFAGS+=-D{{NAME}}" -- that 
> works for compiling the '.o' that gets linked into the kernel executable,
> BUT that make variable is not passed to the (separate!!) compile stage for
> building a.ko module.   Yes, the source-code is compiled _twice_, with the
> resulting .o file in two separate locations, and the options passed to the
> compiler are *NOT* identical in both instances -- they're 'close', but not
> 'exactly the same'.  Is there a good reason why they're different?

You can use DEBUG with makeoptions as a similar hack.  I think that
might also work for modules?

> Is there an 'approved' way for getting a supplemental 'definition' from the
> kernel config file passed to the compile of a loadable module?
> 
> Is there a 'less ugly' way than what I described above, to  get such a 
> definition passed to compilation of a module that will be linked into the
> kernel?
> 
> Ideally, is there a single means/method that will accomplish both tasks?
> 
> Wish-list: something that does _not_ require modifying other files in the
> 'magic data' that config uses?

That is not currently doable. :(

> Peripherally related thereunto, is there a cookbook or other example of 
> making a 'port' for a kernel module, and what all needs to be in it?

Do you need to have these settings be compile options vs loader tunables
/ sysctls?  The latter are preferred if at all possible.

-- 
John Baldwin