netlink stats: Ability to get stats for a single device?

From what I can tell, it's impossible to request stats for a single network device via netlink. When you have thousands of interfaces, this means a lot of wasted effort to get stats for a particular device.

Am I missing something, or do I just need to write up a patch to have netlink pay attention to the ifindex?

Thanks,
Ben

Ben Greear <[email protected]>
Candela Technologies Inc  http://www.candelatech.com

Its already done

rtnl_register(PF_UNSPEC, RTM_GETLINK, rtnl_getlink, rtnl_dump_ifinfo);

From: Ben Greear <[email protected]>
Date: Tue, 26 Oct 2010 12:31:12 -0700

Setting the ->ifi_index or IFLA_IFNAME attribute values appropriately in the getlink request doesn't work?

That should give you back, amonst other things, the rtnl_link_stats for the device in the netlink response.

Yep, it should be easy to change iproute2 to not ask a full dump in ip/ipaddress.c :

if (rtnl_wilddump_request(&rth, preferred_family, RTM_GETLINK) < 0) ...

and instead use rtnl_send() or something like that, if user provided one
specific interface name (or index)

ip link show dev eth0

I'm trying to craft my own netlink message...basically:

   memset(&snl, 0, sizeof(snl));
   snl.nl_family = AF_NETLINK;
   snl.nl_pid    = 0;
   snl.nl_groups = 0;

   memset(&buffer, 0, sizeof(buffer));
   nlh->nlmsg_type = msg_type;
   nlh->nlmsg_flags = NLM_F_MATCH|NLM_F_REQUEST;
   static unsigned int nl_seqno = 1;
   nlh->nlmsg_seq = nl_seqno++;
   nlh->nlmsg_pid = nl_pid;

      nlh->nlmsg_len = NLMSG_LENGTH(sizeof(*ifinfomsg));
      ifinfomsg = (struct ifinfomsg*)(NLMSG_DATA(nlh));
      ifinfomsg->ifi_family = AF_UNSPEC;
      ifinfomsg->ifi_type = IFLA_UNSPEC;
      ifinfomsg->ifi_index = if_index;
      ifinfomsg->ifi_flags = 0;
      ifinfomsg->ifi_change = 0xffffffff;

It's possible that I'm somehow messing this up. But, looking at the static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb) method, I cannot see how it would bail out properly after a single dev has been processed, either.

Thanks,
Ben

Ben Greear <[email protected]>
Candela Technologies Inc  http://www.candelatech.com

dont use F_MATCH : check net/core/rtnetlink.c

vi +1660 net/core/rtnetlink.c

You _dont_ want to call 'dumpit' : so dont use a bit present in NLM_F_DUMP at all:

        if (kind == 2 && nlh->nlmsg_flags&NLM_F_DUMP) {
                struct sock *rtnl;
                rtnl_dumpit_func dumpit;

                dumpit = rtnl_get_dumpit(family, type);
                if (dumpit == NULL)
                        return -EOPNOTSUPP;

                __rtnl_unlock();
                rtnl = net->rtnl;
                err = netlink_dump_start(rtnl, skb, nlh, dumpit, NULL);
                rtnl_lock();
                return err;
        }

You want instead to call the 'doit' handler (one device only)

        doit = rtnl_get_doit(family, type);
        if (doit == NULL)
                return -EOPNOTSUPP;

        return doit(skb, nlh, (void *)&rta_buf[0]);

That was exactly my problem. It works as expected with that NLM_F_MATCH removed.

Thanks!
Ben

Ben Greear <[email protected]>
Candela Technologies Inc  http://www.candelatech.com