Module netlink::multicast_groups

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A module for managing Netlink multicast group memberships.

A Netlink socket can subscribe to any number of multicast groups, as defined by the Netlink protocol family that the socket is connected to. There are two modes of specifying the multicast group memberships. Mode 1 is referred to as “legacy” throughout this module because it was replaced by mode 2, referred to as “modern”, in Linux 2.6.14. Mode 1: Specifying nl_groups, a 32 bit bitmask, when binding the the socket. Mode 2: Setting the NETLINK_ADD_MEMBERSHIP or NETLINK_DROP_MEMBERSHIP socket option.

Note that both mode 1 and mode 2 are supported (for backwards compatibility), and the two modes operate over different sets of constants. The “modern” constants correspond to the index of the set-bit in their “legacy” counterpart. For example, consider this sample of NETLINK_ROUTE constants: RTNLGRP_LINK: legacy (1), modern (1), RTNLGRP_NOTIFY: legacy (2), modern (2), RTNLGRP_NEIGH: legacy (4), modern (3), RTNLGRP_TC: legacy (8), modern (4),

The [MulticastGroupMemberships] struct exposed by this module tracks the memberships independently of the mode via which they are set. For example, a NETLINK_ROUTE client could bind to RTMGRP_IPV6_IFADDR (256), to start receiving IPv6 address events, and later set the NETLINK_DROP_MEMBERSHIP socket option to RTNLGRP_IPV6_IFADDR (9), to stop receiving events.

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