>Number:         36918
>Category:       kern
>Synopsis:       NetBSD 4.0_RC1 __NetBSD_Version__ botch
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Sep 05 14:40:00 +0000 2007
>Originator:     Robert Elz
>Release:        NetBSD 4.0_RC1
>Organization:
	Prince of Songkla University
>Environment:
System: NetBSD jade.coe.psu.ac.th 3.99.15 NetBSD 3.99.15 (GENERIC-1.696-20060125) #8: Wed Jan 25 04:59:39 ICT 2006 kre@jade.coe.psu.ac.th:/usr/obj/current/kernels/JADE_ASUS i386
Architecture: i386
Machine: i386
>Description:
	The value defined (in <sys/param.h>) for __NetBSD_Version__
	is incompatible with the __NetBSD_Prereq__() macro (also in
	param.h)

	IMO this is a release blocking PR.

		(Also note this is a branch specific bug, there is
		no similar problem in -current, nothing here can be
		corrected by any kind of pull up).

>How-To-Repeat:
	Build an LKM (or other similar object).

	In it, do something like

#if __NetBSD_Prereq__(4,0,0)	/* require NB 4.0 or lower */
	/* whatever code */
#endif

	and compile that on a 4.0 RC1 system.   Watch it fail
	(that is, 4.0 RC1 is an "advanced" system over 4.0).

	All that can be done that will work is

#if __NetBSD_Prereq__(4,0,1)	/* require NB 4.0.1 or lower */
	/* whatever code */
#endif

	but that will continue to work with NetBSD 4.0.1 which doesn't
	exist yet (no-one can possibly write code that is guaranteed
	compatible with 4.0.1 - not today).

>Fix:
	There are two possible fixes that are plausible that I can
	see.

	The first is to alter __NetBSD_Prereq__() and give it a 4th
	parameter that would specify the largest value that is OK
	in the final two (used to be MBZ) digits of __NetBSD_Version__.

	That would be, of course, a LKM incompatoble change (an API
	change - and a needed one, as current code cannot be correct)
	which would because of that require a bump of __NetBSD_Version__

	The alternative is simply to bump __NetBSD_Version__ to a value that
	actually works with __NetBSD_Prereq__ - the smallest value that
	fits (which is at least 400000003 - the current value of
	__NetBSD_Version__) is 400000100 - which indicates NetBSD 4.0.1
	(or 4.0.1 RC1 or anything else like that)

	That's what I suggest doing.  Release 4.0.1 instead of 4.0.

	The only real issue is the timing - if it looks fairly certain
	that no more version bumps will be required, then do it now.
	If it seems likely that there might be some other change that
	would require a version bump anyway, wait for that (or until
	it is clear there will be no such event before the release).

Aside:
	It would be good to have a PR category "release" or something
	for bugs specific to release candidates (Beta and RCs) - that is,
	for bugs which occur only in those are aren't in any mainline code.