netdev - Re: [PATCH net-next v1 2/2] bridge: export multicast database via netlink

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Date:	Sat, 01 Dec 2012 11:56:18 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Thomas Graf <tgraf@...g.ch>
Cc:	netdev@...r.kernel.org, bridge@...ts.linux-foundation.org,
	Herbert Xu <herbert@...dor.hengli.com.au>,
	Stephen Hemminger <shemminger@...tta.com>,
	"David S. Miller" <davem@...emloft.net>,
	Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH net-next v1 2/2] bridge: export multicast database via
 netlink

On Fri, 2012-11-30 at 15:27 +0000, Thomas Graf wrote:
> On 11/30/12 at 11:00pm, Cong Wang wrote:
> > I don't understand this. nla_put_flag() is used to put a flag (only one
> > bit set) into a netlink message, so why should we use it to put
> > p->port_no here? And why port_no 0 matters here?
> 
> nla_put_flag() will simply add a netlink attribute with no payload,
> i.e. just the header. Assuming that port_no == 0 is invalid the
> port_no can be used as attribute id as both are 16bit integers.
> 
> It will look like this:
> 
> MDBA_ROUTERS = {
>   {
>     .nla_len = 4,
>     .nla_type = <port_no_1>,
>   },
>   {
>     .nla_len = 4,
>     .nla_type = <port_no_2>,
>   }
>   [...]
> }
> 
> If you ever need to extend this you can just add payload to the
> per port attribute and nothing will break.

Never mind, I will use port->dev->ifindex instead of port->port_no. This
will also make the user-space easier.

> 
> > So I should use net->dev_base_seq + mdb->seq ?
> 
> No you can't, mdb->seq is not stable throughout a dump. What you
> can do is save mdb->seq in cb->args[] and in case you continue
> dumping from the same mdb in the next call to your dump function
> you check if it changed and bump cb->seq if it did to trigger an
> interrupt.

Ok, will do.

Thanks!

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