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    Subject[34-longterm 148/247] arp_notify: unconditionally send gratuitous ARP for NETDEV_NOTIFY_PEERS.
    Date
    From: Ian Campbell <Ian.Campbell@citrix.com>

    -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    If you see a problem with using this for longterm, please comment.
    -------------------

    commit d11327ad6695db8117c78d70611e71102ceec2ac upstream.

    NETDEV_NOTIFY_PEER is an explicit request by the driver to send a link
    notification while NETDEV_UP/NETDEV_CHANGEADDR generate link
    notifications as a sort of side effect.

    In the later cases the sysctl option is present because link
    notification events can have undesired effects e.g. if the link is
    flapping. I don't think this applies in the case of an explicit
    request from a driver.

    This patch makes NETDEV_NOTIFY_PEER unconditional, if preferred we
    could add a new sysctl for this case which defaults to on.

    This change causes Xen post-migration ARP notifications (which cause
    switches to relearn their MAC tables etc) to be sent by default.

    Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
    ---
    net/ipv4/devinet.c | 30 ++++++++++++++++++++----------
    1 files changed, 20 insertions(+), 10 deletions(-)

    diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
    index c12777f..e85d771 100644
    --- a/net/ipv4/devinet.c
    +++ b/net/ipv4/devinet.c
    @@ -1029,6 +1029,21 @@ static inline bool inetdev_valid_mtu(unsigned mtu)
    return mtu >= 68;
    }

    +static void inetdev_send_gratuitous_arp(struct net_device *dev,
    + struct in_device *in_dev)
    +
    +{
    + struct in_ifaddr *ifa = in_dev->ifa_list;
    +
    + if (!ifa)
    + return;
    +
    + arp_send(ARPOP_REQUEST, ETH_P_ARP,
    + ifa->ifa_address, dev,
    + ifa->ifa_address, NULL,
    + dev->dev_addr, NULL);
    +}
    +
    /* Called only under RTNL semaphore */

    static int inetdev_event(struct notifier_block *this, unsigned long event,
    @@ -1081,18 +1096,13 @@ static int inetdev_event(struct notifier_block *this, unsigned long event,
    }
    ip_mc_up(in_dev);
    /* fall through */
    - case NETDEV_NOTIFY_PEERS:
    case NETDEV_CHANGEADDR:
    + if (!IN_DEV_ARP_NOTIFY(in_dev))
    + break;
    + /* fall through */
    + case NETDEV_NOTIFY_PEERS:
    /* Send gratuitous ARP to notify of link change */
    - if (IN_DEV_ARP_NOTIFY(in_dev)) {
    - struct in_ifaddr *ifa = in_dev->ifa_list;
    -
    - if (ifa)
    - arp_send(ARPOP_REQUEST, ETH_P_ARP,
    - ifa->ifa_address, dev,
    - ifa->ifa_address, NULL,
    - dev->dev_addr, NULL);
    - }
    + inetdev_send_gratuitous_arp(dev, in_dev);
    break;
    case NETDEV_DOWN:
    ip_mc_down(in_dev);
    --
    1.7.4.4


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