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net/tipc/group.c
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Merge branch 'tipc-comm-groups'
Jon Maloy says:
====================
tipc: Introduce Communcation Group feature
With this commit series we introduce a 'Group Communication' feature in
order to resolve the datagram and multicast flow control problem. This
new feature makes it possible for a user to instantiate multiple private
virtual brokerless message buses by just creating and joining member
sockets.
The main features are as follows:
---------------------------------
- Sockets can join a group via a new setsockopt() call TIPC_GROUP_JOIN.
If it is the first socket of the group this implies creation of the
group. This call takes four parameters: 'type' serves as group
identifier, 'instance' serves as member identifier, and 'scope'
indicates the visibility of the group (node/cluster/zone). Finally,
'flags' indicates different options for the socket joining the group.
For the time being, there are only two such flags: 1) 'LOOPBACK'
indicates if the creator of the socket wants to receive a copy of
broadcast or multicast messages it sends to the group, 2) EVENTS
indicates if it wants to receive membership (JOINED/LEFT) events for
the other members of the group.
- Groups are closed, i.e., sockets which have not joined a group will
not be able to send messages to or receive messages from members of
the group, and vice versa. A socket can only be member of one group
at a time.
- There are four transmission modes.
1: Unicast. The sender transmits a message using the port identity
(node:port tuple) of the receiving socket.
2: Anycast. The sender transmits a message using a port name (type:
instance:scope) of one of the receiving sockets. If more than
one member socket matches the given address a destination is
selected according to a round-robin algorithm, but also considering
the destination load (advertised window size) as an additional
criteria.
3: Multicast. The sender transmits a message using a port name
(type:instance:scope) of one or more of the receiving sockets.
All sockets in the group matching the given address will receive
a copy of the message.
4: Broadcast. The sender transmits a message using the primtive
send(). All members of the group, irrespective of their member
identity (instance) number receive a copy of the message.
- TIPC broadcast is used for carrying messages in mode 3 or 4 when
this is deemed more efficient, i.e., depending on number of actual
destinations.
- All transmission modes are flow controlled, so that messages never
are dropped or rejected, just like we are used to from connection
oriented communication. A special algorithm guarantees that this is
true even for multipoint-to-point communication, i.e., at occasions
where many source sockets may decide to send simultaneously towards
the same destination socket.
- Sequence order is always guaranteed, even between the different
transmission modes.
- Member join/leave events are received in all other member sockets
in guaranteed order. I.e., a 'JOINED' (an empty message with the OOB
bit set) will always be received before the first data message from
a new member, and a 'LEAVE' (like 'JOINED', but with EOR bit set) will
always arrive after the last data message from a leaving member.
-----
v2: Reordered variable declarations in descending length order, as per
feedback from David Miller. This was done as far as permitted by the
the initialization order.
====================
Signed-off-by: 
David S. Miller <davem@davemloft.net>