netdev - Re: [PATCH] Add support for netconsole driver used on bridge device with VIF attached

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Date:	Mon, 29 Apr 2013 13:42:25 +0300
From:	Yuval Shaia <yuval.shaia@...cle.com>
To:	Ian Campbell <Ian.Campbell@...rix.com>
Cc:	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	bridge@...ts.linux-foundation.org,
	Stephen Hemminger <shemminger@...tta.com>
Subject: Re: [PATCH] Add support for netconsole driver used on bridge
 device with VIF attached

On Tue, 2013-01-29 at 10:29 +0000, Ian Campbell wrote:
> On Tue, 2013-01-29 at 08:54 +0000, Yuval Shaia wrote:
> > > Please can you explain the exact code path which results in this new
> > > hook being called.
> > > 
> > init_netconsole() in netconsole.c -> alloc_param_target() -> netpoll_setup() 
> > in netpoll.c -> __netpoll_setup() which check if ndo_poll_controller() 
> > operation is supported.
> 
> Are you sure this is being called for the VIF interface? In your
> configuration I'd expect it to be called on the bridge not the vif, or
> at least for calling on the VIF to not impact whether netpool was
> enabled for the bridge or not.
> 
> I think the underlying issue which you are seeing is that
> br_netpoll_setup() requires that all members of the bridge support
> netpoll before allowing netpoll to be enabled on the bridge itself. 
> 
> This seems like an odd restriction in the bridge driver since in
> principal only the port over which the netpoll traffic will be going
> will need netpoll, but perhaps the bridge can't tell which port that is
> or is going to be? I think it is worth discussing this with the bridge
> maintainers (who I have CC'd, threads starts at
> http://marc.info/?l=linux-netdev&m=135878868112700&w=2)
> 
> Hopefully the bridge isn't flooding/broadcasting netpoll to all ports,
> at least in the case where DST IP and MAC have been specified. That
> would be rather inefficient, especially when most ports go to virtual
> machines.
> 
> So before I ack this patch I'd like to hear back from the bridge
> maintainers about whether the current behaviour in the bridge is
> intended and whether it could be fixed in some better way than adding
> netpoll to netback.
Ian,
Can you suggest how to continue from here? as i don't see any comment on
that issue up to now.
Yuval
> 
> AFAICT the only reason to actually support netpoll in netback would be
> if you wanted host logs to go to a listener running in a domain on the
> same host, which sounds like a mad idea to me! If someone actually has a
> real need for that use case and can test that it works I'd be happy to
> reconsider this patch on that basis (assuming the necessary #ifdefs are
> added as mentioned before).
> 
> > > BTW looking at the patch as it is any use of this hook should be wrapped
> > > in CONFIG_NET_POLL_CONTROLLER.
> > > 
> > > Ian.
> > > 
> > 
> > 
> 
> 



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