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

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Date:	Sat, 13 Jun 2009 19:18:05 -0700
From:	"Michael Chan" <mchan@...adcom.com>
To:	"James Bottomley" <James.Bottomley@...senPartnership.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 18:33 -0700, James Bottomley wrote:
> 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.

Yeah, the plan is to have a bnx2x_cnic_probe() when we add support for
that.  There will be a separate init_bnx2x_cnic() because the hardware
interface is not exactly the same.

> 
> 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.
> 

This will require some additional infra-structure.  We can look into
this when we support the 10G driver.  Thanks.


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