netdev - Re: [PATCH 2/2] ipvlan: always allow the broadcast MAC address

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Date:	Fri, 27 Mar 2015 17:52:16 -0700
From:	Mahesh Bandewar <maheshb@...gle.com>
To:	Dan Williams <dcbw@...hat.com>
Cc:	linux-netdev <netdev@...r.kernel.org>, jbenc@...hat.com
Subject: Re: [PATCH 2/2] ipvlan: always allow the broadcast MAC address

On Thu, Mar 26, 2015 at 3:43 PM, Dan Williams <dcbw@...hat.com> wrote:
> ipvlan currently fails DHCP addressing for two reasons:
>
> 1) DHCP offers are typically unicast back to the device's MAC
> address, and at the IP layer have a destination IP address
> matching the new lease address.  In ipvlan unicast packets
> are checked against existing addresses assigned to the ipvlan
> interface, so clearly this fails hard because the ipvlan
> interface has no IP addresses yet.  Workaround: request
> that the server broadcast replies (-B for dhclient), which
> don't get checked against the IP address list.
>
> 2) Even when that's done, mac_filters only allows the
> broadcast MAC address when the interface has >= 1 IPv4
> addresses, so double-fail, and the incoming DHCP offer
> gets dropped on the floor again.
>
> Instead of doing ugly stuff like watching for outgoing DHCP
> requests and adding the broadcast MAC to mac_filters for
> a period of time, just always allow the broadcast MAC.  This
> lets the ipvlan interface be configured with DHCP in
> Layer2 mode as long as as broadcast replies are used.
>
Guys, stop thinking that we live in IPv4-only world! Think about a
hybrid environment where all your IPvlan slaves are IPv6 only while
your network has IPv4 (with crap-load of broadcast traffic) and IPv6
traffic. In that situation IPvlan demuxer has to forward all that
broadcast-traffic to it's slaves which they don't care at all.

I agree that the current driver falls short of handling DHCPv4 and
needs a fix. But for couple of initial config packets, it's not wise
to loose the performance forever. I don't like this patch.


> Signed-off-by: Dan Williams <dcbw@...hat.com>
> ---
>  drivers/net/ipvlan/ipvlan_main.c | 21 ++++-----------------
>  1 file changed, 4 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/net/ipvlan/ipvlan_main.c b/drivers/net/ipvlan/ipvlan_main.c
> index d34f580..787d7fb 100644
> --- a/drivers/net/ipvlan/ipvlan_main.c
> +++ b/drivers/net/ipvlan/ipvlan_main.c
> @@ -214,17 +214,6 @@ static void ipvlan_change_rx_flags(struct net_device *dev, int change)
>                 dev_set_allmulti(phy_dev, dev->flags & IFF_ALLMULTI? 1 : -1);
>  }
>
> -static void ipvlan_set_broadcast_mac_filter(struct ipvl_dev *ipvlan, bool set)
> -{
> -       struct net_device *dev = ipvlan->dev;
> -       unsigned int hashbit = ipvlan_mac_hash(dev->broadcast);
> -
> -       if (set && !test_bit(hashbit, ipvlan->mac_filters))
> -               __set_bit(hashbit, ipvlan->mac_filters);
> -       else if (!set && test_bit(hashbit, ipvlan->mac_filters))
> -               __clear_bit(hashbit, ipvlan->mac_filters);
> -}
> -
>  static void ipvlan_set_multicast_mac_filter(struct net_device *dev)
>  {
>         struct ipvl_dev *ipvlan = netdev_priv(dev);
> @@ -239,11 +228,11 @@ static void ipvlan_set_multicast_mac_filter(struct net_device *dev)
>                 netdev_for_each_mc_addr(ha, dev)
>                         __set_bit(ipvlan_mac_hash(ha->addr), mc_filters);
>
> +               /* always allow broadcast frames */
> +               __set_bit(ipvlan_mac_hash(dev->broadcast), mc_filters);
> +
>                 bitmap_copy(ipvlan->mac_filters, mc_filters,
>                             IPVLAN_MAC_FILTER_SIZE);
> -
> -               if (ipvlan->ipv4cnt)
> -                       ipvlan_set_broadcast_mac_filter(ipvlan, true);
>         }
>         dev_uc_sync(ipvlan->phy_dev, dev);
>         dev_mc_sync(ipvlan->phy_dev, dev);
> @@ -470,6 +459,7 @@ static int ipvlan_link_new(struct net *src_net, struct net_device *dev,
>         INIT_LIST_HEAD(&ipvlan->addrs);
>         ipvlan->ipv4cnt = 0;
>         ipvlan->ipv6cnt = 0;
> +       __set_bit(ipvlan_mac_hash(dev->broadcast), ipvlan->mac_filters);
>
>         /* TODO Probably put random address here to be presented to the
>          * world but keep using the physical-dev address for the outgoing
> @@ -694,7 +684,6 @@ static int ipvlan_add_addr4(struct ipvl_dev *ipvlan, struct in_addr *ip4_addr)
>         list_add_tail_rcu(&addr->anode, &ipvlan->addrs);
>         ipvlan->ipv4cnt++;
>         ipvlan_ht_addr_add(ipvlan, addr);
> -       ipvlan_set_broadcast_mac_filter(ipvlan, true);
>
>         return 0;
>  }
> @@ -711,8 +700,6 @@ static void ipvlan_del_addr4(struct ipvl_dev *ipvlan, struct in_addr *ip4_addr)
>         list_del_rcu(&addr->anode);
>         ipvlan->ipv4cnt--;
>         WARN_ON(ipvlan->ipv4cnt < 0);
> -       if (!ipvlan->ipv4cnt)
> -           ipvlan_set_broadcast_mac_filter(ipvlan, false);
>         kfree_rcu(addr, rcu);
>
>         return;
> --
> 2.1.0
>
>
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