linux-kernel - Re: -git tree build failure #2: drivers/net/cnic.c:2520: error: implicit declaration of function ‘__symbol

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Message-Id: <1244943216.5323.86.camel@mulgrave.site>
Date:	Sat, 13 Jun 2009 20:33:36 -0500
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Michael Chan <mchan@...adcom.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	linux-scsi <linux-scsi@...r.kernel.org>
Subject: Re: -git tree build failure #2: drivers/net/cnic.c:2520: error:
 implicit declaration of function
 ‘__symbol_get’

On Sat, 2009-06-13 at 17:43 -0700, Michael Chan wrote:
> On Sat, 2009-06-13 at 13:42 -0700, James Bottomley wrote:
> > On Sat, 2009-06-13 at 13:11 -0700, Linus Torvalds wrote:
> > > 
> > > 
> > > That makes no sense. 
> > > 
> > > Look at the first #include in the file - it already includes 
> > > <linux/module.h>.
> > > 
> > > Why do we need to do it twice?
> > 
> > We don't ... it's the wrong fix.  The actual problem is that
> > __symbol_get() is only defined for the modular case.  What it looks to
> > be doing is a reflection call on bnx2_cnic_probe().  I'm not sure why
> > it's doing this ... other than perhaps cnic wants to avoid an explicit
> > bnx2 dependency?  I actually think it's incorrect, since the netdev code
> > before it just checked bnx2 is present, so I see no harm in an explicit
> > call, so this should fix it.
> > 
> > If it had a good reason for the reflective call, then symbol_get()
> > without the __ should be used.
> > 
> > Michael Chan, could you confirm?
> > 
> Thanks James and Ingo.  We don't want to have a symbol dependency on
> bnx2 because this driver eventually will support the 10G bnx2x driver as
> well.  So we want the driver to support either or both NIC drivers
> without both drivers loaded.  Please use the patch below.

Um, but that's not going to work very well.  When you have your 10G
driver, they'll both have to export the symbol name bnx2_cnic_probe
which the kernel isn't going to like.  You can differentiate the symbols
and add a multiple symbol lookup in init_bnx2_cnic(), but that's getting
ugly.

What about doing something more standard, like bus matching?  That's how
the SCSI upper layer drivers work:  we export a virtual SCSI bus and
they bind to it if a supporting device appears.  You could do something
similar exporting a virtual cnic bus from your network drivers and get
the cnic driver to bind to it.

James


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