net: igmp: Reduce Unsolicited report interval to 1s when using IGMPv3
If an IGMP join packet is lost you will not receive data sent to the multicast group so if no data arrives from that multicast group in a period of time after the IGMP join a second IGMP join will be sent. The delay between joins is the "IGMP Unsolicited Report Interval". Previously this value was hard coded to be chosen randomly between 0-10s. This can be too long for some use-cases, such as IPTV as it can cause channel change to be slow in the presence of packet loss. The value 10s has come from IGMPv2 RFC2236, which was reduced to 1s in IGMPv3 RFC3376. This patch makes the kernel use the 1s value from the later RFC if we are operating in IGMPv3 mode. IGMPv2 behaviour is unaffected. Tested with Wireshark and a simple program to join a (non-existent) multicast group. The distribution of timings for the second join differ based upon setting /proc/sys/net/ipv4/conf/eth0/force_igmp_version. Signed-off-by: NWilliam Manley <william.manley@youview.com> Acked-by: NHannes Frederic Sowa <hannes@stressinduktion.org> Acked-by: NBenjamin LaHaise <bcrl@kvack.org> Signed-off-by: NDavid S. Miller <davem@davemloft.net>
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