netdev - Re: Fun with if_bridge.h and br

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Date:	Mon, 3 May 2010 13:36:13 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	netdev@...r.kernel.org, arnd@...db.de
Subject: Re: Fun with if_bridge.h and br_private.h

On Mon, 3 May 2010 12:12:56 -0700
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:

> Hello, Stephen,
> 
> I need some help with #include issues surrounding bridge.
> 
> Arnd has been putting together a sparse-based RCU-checking tool
> that can detect pointer access that should have been protected by an
> rcu_dereference() or rcu_assign_pointer().  On of the side-effects of
> his approach is that rcu_dereference() can no longer handle pointers
> to incomplete types, as Arnd's approach uses the address-space feature
> of sparse, which in turn must tag the type pointed to rather than the
> pointer itself.  And this in turn requires rcu_dereference() and friends
> to see the pointed-to type as well as the pointer type.
> 
> One place affected by this is handle_bridge() in net/core/dev.c, which
> invokes rcu_dereference() on skb->dev->br_port, which is of type struct
> net_bridge_port, which is defined in net/bridge/br_private.h.  This is,
> well, private, but is included into a couple places in netfilter and atm,
> so I tried including it into net/core/dev.c.
> 
> This still left me with forward references:
> 
> In file included from net/core/dev.c:104:
> include/linux/if_bridge.h:106: warning: "struct net_bridge_port" declared inside parameter list
> include/linux/if_bridge.h:106: warning: its scope is only this definition or declaration, which is probably not what you want
> net/core/dev.c:2331: error: conflicting types for "br_handle_frame_hook"
> include/linux/if_bridge.h:105: error: previous declaration of "br_handle_frame_hook" was here
> net/core/dev.c:2333: error: conflicting types for "br_handle_frame_hook"
> include/linux/if_bridge.h:105: error: previous declaration of "br_handle_frame_hook" was here
> 
> This happens because net/bridge/br_private.h includes if_bridge.h before
> it defines net_bridge_port.
> 
> Any thoughts on how best to allow handle_bridge() see the definition
> of struct net_bridge_port?
> 

Why not make it a void *, there is no reason to make core code depend
on br_private.h.
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