linux-kernel - Re: [v4l-dvb-maintainer] bttv build error (CONFIG

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Date:	Wed, 31 Oct 2007 09:23:50 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Trent Piepho <xyzzy@...akeasy.org>
Cc:	lkml <linux-kernel@...r.kernel.org>, v4l-dvb-maintainer@...uxtv.org
Subject: Re: [v4l-dvb-maintainer] bttv build error (CONFIG_NET=n)

On Wed, 31 Oct 2007 04:51:45 -0700 (PDT) Trent Piepho wrote:

> On Tue, 30 Oct 2007, Randy Dunlap wrote:
> > drivers/media/video/bt8xx/bttv-cards.c calls ip_compute_csum().
> > However, when CONFIG_NET=n, that produces:
> >
> > ERROR: "ip_compute_csum" [drivers/media/video/bt8xx/bttv.ko] undefined!
> >
> > Config symbol VIDEO_BT848 can be made to depend on NET, or the
> > osprey_eeprom() function can be built depending on some new config
> > symbol, or bttv could have its own checksum function...
> 
> The real problem here is that ip_compute_csum is part of lib-y, but is also
> exported for modules.  This problem has come up before, for instance your
> patch for csum_partial()
> http://lkml.org/lkml/2007/4/3/209
> 
> Or the problem with kasprintf and the lg module:
> http://lkml.org/lkml/2007/9/24/15
> 
> The general lib-y vs EXPORT_SYMBOL problem:
> http://lkml.org/lkml/2007/9/25/17
> 
> The only reason the net stuff works, is because CONFIG_NET includes igmp.c,
> which can't be compiled as a module.  That means ip_compute_csum() will get
> pulled out of the lib.a file for igmp, and thus be present for the net modules
> that use it too.  If igmp could be turned off, made a module, or stopped using
> ip_compute_csum(), then the users of ip_compute_csum() that do depend on
> CONFIG_NET would have the same problem as bttv does.

Thanks for the analysis and summary.
(I'm still waiting for those lkml.org links to load... timed out)

> It seems a shame to create a new ip checksum function in the bttv driver when
> a perfectly good one already exists and will already be present in just about
> every kernel out there.  Honestly, how common is NET=n and VIDEO_BT848=m
> outside of randconfig?

so just adding "depends on NET" should be OK then?

---
~Randy
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