Subject: Re: how facilitate custom driver development: the cdevsw/conf.c problem
To: None <tech-kern@NetBSD.ORG>
From: Chris Torek <torek@BSDI.COM>
List: current-users
Date: 09/07/1997 18:59:51
>...  [I realize that most of arch/foo/foo/conf.c could be generated,
>but I don't think we are ready for that yet]

Hm... did I ever describe the config code in BSD/OS that does this?

Here are a few lines from my sparc/conf/ioconf.c.sparc file, for
an example:

	 * Template ioconf.c for sparc.

	#include <sys/param.h>
	#include <sys/conf.h>
	#include <sys/device.h>
	#include <sys/vnode.h>


	extern struct devsw cnsw, cttysw, mmsw, swapsw, logsw, devfdsw;
	extern struct devsw ptssw, ptcsw;
	extern struct devsw mssw, fbsw, kbdsw, openpromsw;


	 * The table here is derived from Sun's /dev/MAKEDEV.  I am not sure
	 * what all of these are, but if we stick to Sun's numbering, we should
	 * be pretty well off.
	struct devsw *devsw[] = {
		&cnsw,			/* 0 = virtual console */
		NULL,			/* 1 = "oct" tty */
		&cttysw,		/* 2 = controlling terminal */
		%DEVSW(pty, &ptssw),	/* 20 = pseudo-tty slave */
		%DEVSW(pty, &ptcsw),	/* 21 = pseudo-tty master */
		%DEVSW(fd),		/* 54 = floppy */
		%DEVSW(cgthree),	/* 55 = /dev/cgthree */

There are four %-keywords that are decoded here:

	%CONFIG		emits the configuration (cfdata, locators, etc.).

	%DECLSW		emits "extern struct devsw XXsw" for all
			configured devices.

	%DEVSW(x)	emits &xxsw if device x is configured, else NULL
	%DEVSW(x,y)	emits y if device x is configured, else NULL

	%IFSEL(x,y)	emits y if option x is selected, else NULL
	%IFSEL(x,y,z)	emits y if option x is selected, else z

This is pretty simple yet flexible -- for instance, you can do:

	int dougs_special_weird_mode = %IFSEL(dougsmode,1,0);

which will set `dougs_special_weird_mode' under `options DOUGSMODE'.

Note that y and z may not contain commas (and, in my current
implementation, spaces are dropped too, mainly as a side effect).

There are, of course, a bunch of related changes (no more separate
bdevsw and cdevsw, the devsw array is a table of pointers, and each
driver defines its own XXsw structure).