[CONNECTOR]: Update documentation to match reality.
Updated documentation to reflect 2.6.14 netlink changes
about socket options, multicasting and group number.
Please concider for 2.6.14.
Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/Documentation/connector/connector.txt b/Documentation/connector/connector.txt
index 54a0a14b..57a314b 100644
--- a/Documentation/connector/connector.txt
+++ b/Documentation/connector/connector.txt
@@ -131,3 +131,47 @@
be lost due to memory pressure or process' receiving queue overflowed,
so caller is warned must be prepared. That is why struct cn_msg [main
connector's message header] contains u32 seq and u32 ack fields.
+
+/*****************************************/
+Userspace usage.
+/*****************************************/
+2.6.14 has a new netlink socket implementation, which by default does not
+allow to send data to netlink groups other than 1.
+So, if to use netlink socket (for example using connector)
+with different group number userspace application must subscribe to
+that group. It can be achieved by following pseudocode:
+
+s = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR);
+
+l_local.nl_family = AF_NETLINK;
+l_local.nl_groups = 12345;
+l_local.nl_pid = 0;
+
+if (bind(s, (struct sockaddr *)&l_local, sizeof(struct sockaddr_nl)) == -1) {
+ perror("bind");
+ close(s);
+ return -1;
+}
+
+{
+ int on = l_local.nl_groups;
+ setsockopt(s, 270, 1, &on, sizeof(on));
+}
+
+Where 270 above is SOL_NETLINK, and 1 is a NETLINK_ADD_MEMBERSHIP socket
+option. To drop multicast subscription one should call above socket option
+with NETLINK_DROP_MEMBERSHIP parameter which is defined as 0.
+
+2.6.14 netlink code only allows to select a group which is less or equal to
+the maximum group number, which is used at netlink_kernel_create() time.
+In case of connector it is CN_NETLINK_USERS + 0xf, so if you want to use
+group number 12345, you must increment CN_NETLINK_USERS to that number.
+Additional 0xf numbers are allocated to be used by non-in-kernel users.
+
+Due to this limitation, group 0xffffffff does not work now, so one can
+not use add/remove connector's group notifications, but as far as I know,
+only cn_test.c test module used it.
+
+Some work in netlink area is still being done, so things can be changed in
+2.6.15 timeframe, if it will happen, documentation will be updated for that
+kernel.