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    Subject[PATCH 3.16 393/410] ip_tunnel: Emit events for post-register MTU changes
    3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Petr Machata <petrm@mellanox.com>

    commit f6cc9c054e77b9a28d4594bcc201697edb21dfd2 upstream.

    For tunnels created with IFLA_MTU, MTU of the netdevice is set by
    rtnl_create_link() (called from rtnl_newlink()) before the device is
    registered. However without IFLA_MTU that's not done.

    rtnl_newlink() proceeds by calling struct rtnl_link_ops.newlink, which
    via ip_tunnel_newlink() calls register_netdevice(), and that emits
    NETDEV_REGISTER. Thus any listeners that inspect the netdevice get the
    MTU of 0.

    After ip_tunnel_newlink() corrects the MTU after registering the
    netdevice, but since there's no event, the listeners don't get to know
    about the MTU until something else happens--such as a NETDEV_UP event.
    That's not ideal.

    So instead of setting the MTU directly, go through dev_set_mtu(), which
    takes care of distributing the necessary NETDEV_PRECHANGEMTU and
    NETDEV_CHANGEMTU events.

    Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
    Signed-off-by: Petr Machata <petrm@mellanox.com>
    Signed-off-by: Ido Schimmel <idosch@mellanox.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    [bwh: Backported to 3.16: Resolve conflict with commit 24fc79798b8d
    "ip_tunnel: Clamp MTU to bounds on new link", referring to commit
    5568cdc368c3 "ip_tunnel: Resolve ipsec merge conflict properly."]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    --- a/net/ipv4/ip_tunnel.c
    +++ b/net/ipv4/ip_tunnel.c
    @@ -405,17 +405,26 @@ static struct ip_tunnel *ip_tunnel_creat
    {
    struct ip_tunnel *nt;
    struct net_device *dev;
    + int mtu;
    + int err;

    BUG_ON(!itn->fb_tunnel_dev);
    dev = __ip_tunnel_create(net, itn->fb_tunnel_dev->rtnl_link_ops, parms);
    if (IS_ERR(dev))
    return ERR_CAST(dev);

    - dev->mtu = ip_tunnel_bind_dev(dev);
    + mtu = ip_tunnel_bind_dev(dev);
    + err = dev_set_mtu(dev, mtu);
    + if (err)
    + goto err_dev_set_mtu;

    nt = netdev_priv(dev);
    ip_tunnel_add(itn, nt);
    return nt;
    +
    +err_dev_set_mtu:
    + unregister_netdevice(dev);
    + return ERR_PTR(err);
    }

    int ip_tunnel_rcv(struct ip_tunnel *tunnel, struct sk_buff *skb,
    @@ -962,7 +971,7 @@ int ip_tunnel_newlink(struct net_device
    nt->parms = *p;
    err = register_netdevice(dev);
    if (err)
    - goto out;
    + goto err_register_netdevice;

    if (dev->type == ARPHRD_ETHER && !tb[IFLA_ADDRESS])
    eth_hw_addr_random(dev);
    @@ -971,15 +980,20 @@ int ip_tunnel_newlink(struct net_device
    if (tb[IFLA_MTU]) {
    unsigned int max = 0xfff8 - dev->hard_header_len - nt->hlen;

    - dev->mtu = clamp(dev->mtu, (unsigned int)ETH_MIN_MTU,
    - (unsigned int)(max - sizeof(struct iphdr)));
    - } else {
    - dev->mtu = mtu;
    + mtu = clamp(dev->mtu, (unsigned int)ETH_MIN_MTU,
    + (unsigned int)(max - sizeof(struct iphdr)));
    }

    + err = dev_set_mtu(dev, mtu);
    + if (err)
    + goto err_dev_set_mtu;
    +
    ip_tunnel_add(itn, nt);
    + return 0;

    -out:
    +err_dev_set_mtu:
    + unregister_netdevice(dev);
    +err_register_netdevice:
    return err;
    }
    EXPORT_SYMBOL_GPL(ip_tunnel_newlink);
    \
     
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