toolchain/50051: config(1) can no longer deselect filesystems properly

[dholland%netbsd.org@localhost]

>Number:         50051
>Category:       toolchain
>Synopsis:       config(1) can no longer deselect filesystems properly
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    toolchain-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Jul 16 08:30:00 +0000 2015
>Originator:     David A. Holland
>Release:        NetBSD 7.99.20 (20150716)
>Organization:
>Environment:
System: NetBSD homeworld.netbsd.org 6.1_STABLE NetBSD 6.1_STABLE (NBMAIL) #0: Sun Dec 7 15:42:53 UTC 2014 spz%franklin.NetBSD.org@localhost:/home/netbsd/6/amd64/obj/sys/arch/amd64/compile/NBMAIL amd64
Architecture: x86_64
Machine: amd64
>Description:

Commenting out "file-system FFS" does not produce the same
configuration as writing "file-system FFS" then "no file-system FFS".

In particular, in the latter case 'ufs' is still selected by config
and some (but not all) of sys/ufs/ufs/*.c is built; this then causes
link failure. (The link failure is itself a bug, but this config issue
is substantially more important.)

The problem seems to be that 'no file-system' is no longer a complete
inverse operation. With sufficient -d flags (the -d flag is
undocumented, which is also a bug), observe:

   nbconfig -d -d -d -d GENERIC
     :
   GENERIC:150: debug: fs selected `FFS'
   GENERIC:150: debug: attr selected `uvm'
   GENERIC:150: debug: attr selected `machdep'
   GENERIC:150: debug: attr selected `kern'
   GENERIC:150: debug: attr selected `vfs'
   GENERIC:150: debug: attr selected `ufs'
   GENERIC:150: debug: attr selected `uvm'
   GENERIC:150: debug: attr selected `machdep'
   GENERIC:150: debug: attr selected `kern'
   GENERIC:150: debug: attr selected `vfs'
   GENERIC:150: debug: attr selected `ffs'
   GENERIC:151: debug: deselecting fs `FFS'
   GENERIC:151: debug: opt `FFS' deselected
   GENERIC:151: debug: opt `ffs' deselected
     :

Note that these are not inverses and in particular ufs is left behind.
(All those other things are left behind too but they're going to be
getting included anyway so they aren't noticeable...)

It is not clear when this bug was introduced; last fall's config
changes seem the most likely culprit. The lfs/ufs split, finished in
June 2013, is an absolute upper bound because at the time I was very
careful about being able to build kernels that had no ufs*.o files in
them, or even any ufs_* symbols.

If the problem doesn't affect -7, it almost certainly implicates last
fall's config changes. However, I'm still checking this as I don't
have a -7 tools built right now.

>How-To-Repeat:

To see this in its full glory, comment out FFS, MFS, and EXT2FS from
the amd64 GENERIC, run config, and do 'grep ufs Makefile' in the build
dir.

Then repeat with MFS and EXT2FS still commented out and instead of
commenting out FFS, add 'no file-system FFS' right after the
'file-system FFS' line. Run config, repeat the grep, watch four files
from sys/ufs/ufs appear. (Then build the resulting config and watch it
fail on ufs_truncate.)

>Fix:

Not sure.