netdev - Re: NETPOLL=y , NETDEVICES=n compile error ( Re: 2.6.23-rc1-mm1 )

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Date:	Thu, 2 Aug 2007 17:10:27 +0530 (IST)
From:	Satyam Sharma <satyam@...radead.org>
To:	Sam Ravnborg <sam@...nborg.org>
cc:	Matt Mackall <mpm@...enic.com>, Jarek Poplawski <jarkao2@...pl>,
	Gabriel C <nix.or.die@...glemail.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netdev@...r.kernel.org, jason.wessel@...driver.com,
	amitkale@...syssoft.com, zippel@...ux-m68k.org, jengelh@....de
Subject: Re: NETPOLL=y , NETDEVICES=n compile error ( Re: 2.6.23-rc1-mm1 )

[ Read through the thread, looked at Kconfig files,
  did some tests. Adding Kconfig experts to Cc: list. ]

> On Thu, 2 Aug 2007, Sam Ravnborg wrote:
> 
> > > > 
> > > > ...
> > > > endif # NETDEVICES
> > > > 
> > > > config NETPOLL
> > > >         depends on NETDEVICES
> > > >         def_bool NETCONSOLE
> > > > 
> > > > config NETPOLL_TRAP
> > > >         bool "Netpoll traffic trapping"
> > > >         default n
> > > >         depends on NETPOLL
> > > > 
> > > > config NET_POLL_CONTROLLER
> > > >         def_bool NETPOLL
> > > >         depends on NETPOLL

Gargh, what we're seeing here is a whole bunch of bugs, I think. First
I thought this must be one of those randconfig-producing-wrong-configs
issues, but surprisingly, running "make oldconfig" on this .config on
a fresh 2.6.23-rc1-mm1 tree didn't change anything in the .config.

Kconfig bug #1:
===============

Which means, although:

*****
menuconfig BAZ

if BAZ

config BAR

endif
*****

is widely believed (by most folks, I've heard this on several threads,
and as written in the comment in drivers/net/Kconfig) to be equivalent to:

*****
menuconfig BAZ

if BAZ
endif

config BAR
	depends on BAZ
*****

this is *not* enforced by "make oldconfig"! And hence, the NETPOLL &&
!NETDEVICES situation we're seeing here.

[ We could also categorize this as a bug in Kconfig's "if", fwiw. ]

Kconfig bug #2:
===============

config FOO
	def_bool BAR

is supposed to ensure that FOO == BAR (as Matt mentioned earlier).

However, even this is *not* enforced by "make oldconfig". And hence,
the NETPOLL && !NET_POLL_CONTROLLER situation we're seeing here.

In fact, I believe it's possible to even pass a NETCONSOLE but
!NETPOLL kind of .config through "make oldconfig" but it still won't
catch it, and build breakages *will* occur.

[ We could also categorize this as a bug in Kconfig's "def_bool", fwiw. ]

Possibly, we could also decide to just blame "randconfig" for the whole
issue, and forget about these, because I think it's highly unlikely
(though not impossible) for people with "real" .configs to hit the
problems we saw above.

KGDBOE bug #1:
==============

config KGDBOE in lib/Kconfig.kgdb must also "depend on" NETDEVICES,
and select NET_POLL_CONTROLLER also.

KGDBOE bug #2:
==============

config KGDBOE_NOMODULE is a sad, sad option, and must be killed. The
"if !KGDBOE_NOMODULE" in KGDBOE must be removed, and it must lose its
dependency on "m".

Satyam
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