hdlc: fix compile problem

On Thu, 08 Jan 2009 02:00:00 +0100
Krzysztof Halasa <khc@pm.waw.pl> wrote:

> Stephen Hemminger <shemminger@vyatta.com> writes:
> 
> > It was introduced (by me) in previous patch. Since that isn't applied yet,
> > I'll go back and fix.
> 
> I can see it now, I must have missed it because of the "synclink"
> subject.
> 
> @@ -106,7 +98,7 @@ static int hdlc_device_event(struct noti
>         if (dev_net(dev) != &init_net)
>                 return NOTIFY_DONE;
>  
> -       if (dev->get_stats != hdlc_get_stats)
> +       if (dev->header_ops != &hdlc_null_ops)
>                 return NOTIFY_DONE; /* not an HDLC device */
> 
> This won't work because hdlc_null_ops may be substituted by
> cisco_header_ops or ppp_header_ops. Current test works for now but is
> wrong, too, at least for wanxl driver (it tries to use its
> get_stats()).
> 
> Perhaps some
> +       if (dev->header_ops->something != &something)
> would do? Alternatively we can return to hdlc_carrier_on|off() and
> hdlc_device_event() won't be needed.
> 
> Essentially, it's a bit hard to check if the device is one of ours if
> we are the middle layer.
> 
> 
> There are two layers here:
> - hardware drivers (10+)
> - protocol drivers (5 - hdlc* files)
> 
> Protocol drivers want to define things like:
> - dev->header_ops (no problem)
> - dev->change_mtu (perhaps)
> - dev->hard_start_xmit
> 
> Hardware drivers need to define the rest of NDO.
> 
> Hmm, not much, only hard_start_xmit() is really problematic. I think
> we need a trampoline: hw driver will define the NDO and set
> hard_start_xmit and possibly change_mtu to (exported by hdlc.c)
> hdlc_xmit (hdlc_change_mtu), and hdlc_start_xmit will just call
> protocol's xmit().
> We could also use it for the test in hdlc_device_event:
> 	if (dev->netdev_ops->start_hard_xmit != hdlc_xmit)
> 
> If we could then get rid of this special xmit() and do all header and
> TX preparations in hard_header(), it would be even better (cleaner)
> though IIRC it requires some changes to Ethernet(?) code.
> 
> 
> The changes have to be applied to the 4 synclink drivers and to most
> .c files in drivers/net/wan simultaneously, perhaps it's more practical
> if I do it?

Alternatively, how about this:



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Stephen Hemminger <shemminger@vyatta.com> writes:

> Alternatively, how about this:
>
> --- a/drivers/net/wan/hdlc.c	2009-01-07 17:04:52.002497019 -0800
> +++ b/drivers/net/wan/hdlc.c	2009-01-07 17:07:02.874497531 -0800
> @@ -40,8 +40,6 @@
>  
>  static const char* version = "HDLC support module revision 1.22";
>  
> -static const struct header_ops hdlc_null_ops;
> -
>  #undef DEBUG_LINK
>  
>  static struct hdlc_proto *first_proto;
> @@ -100,7 +98,7 @@ static int hdlc_device_event(struct noti
>  	if (dev_net(dev) != &init_net)
>  		return NOTIFY_DONE;
>  
> -	if (dev->header_ops != &hdlc_null_ops)
> +	if (dev->priv_flags & IFF_WAN_HDLC)
>  		return NOTIFY_DONE; /* not an HDLC device */
>  
>  	if (event != NETDEV_CHANGE)

"dev->netdev_ops->start_hard_xmit != hdlc_xmit" is a dirty hack.
IFF_WAN_HDLC is much cleaner though it's an additional bit consumed.
Sure, I like it.

From: Krzysztof Halasa <khc@pm.waw.pl>
Date: Thu, 08 Jan 2009 02:26:31 +0100

> "dev->netdev_ops->start_hard_xmit != hdlc_xmit" is a dirty hack.
> IFF_WAN_HDLC is much cleaner though it's an additional bit consumed.
> Sure, I like it.

Ok, Stephen please formally resubmit this final version with
full commit message etc..

Thanks.
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>> The changes have to be applied to the 4 synclink drivers and to most
>> .c files in drivers/net/wan simultaneously, perhaps it's more practical
>> if I do it?

Ok, I will do.