[NETLINK]: Add notification message sending interface

Adds nlmsg_notify() implementing proper notification logic. The
message is multicasted to all listeners in the group. The
applications the requests orignates from can request a unicast
back report in which case said socket will be excluded from the
multicast to avoid duplicated notifications.

nlmsg_multicast() is extended to take allocation flags to
allow notification in atomic contexts.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 34 insertions, 2 deletions

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 0f36ddc0b72d..a80e4456e204 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1549,6 +1549,38 @@ void netlink_queue_skip(struct nlmsghdr *nlh, struct sk_buff *skb)
         skb_pull(skb, msglen);
 }
 
+/**
+ * nlmsg_notify - send a notification netlink message
+ * @sk: netlink socket to use
+ * @skb: notification message
+ * @pid: destination netlink pid for reports or 0
+ * @group: destination multicast group or 0
+ * @report: 1 to report back, 0 to disable
+ * @flags: allocation flags
+ */
+int nlmsg_notify(struct sock *sk, struct sk_buff *skb, u32 pid,
+                 unsigned int group, int report, gfp_t flags)
+{
+        int err = 0;
+
+        if (group) {
+                int exclude_pid = 0;
+
+                if (report) {
+                        atomic_inc(&skb->users);
+                        exclude_pid = pid;
+                }
+
+                /* errors reported via destination sk->sk_err */
+                nlmsg_multicast(sk, skb, exclude_pid, group, flags);
+        }
+
+        if (report)
+                err = nlmsg_unicast(sk, skb, pid);
+
+        return err;
+}
+
 #ifdef CONFIG_PROC_FS
 struct nl_seq_iter {
         int link;
@@ -1802,4 +1834,4 @@ EXPORT_SYMBOL(netlink_set_err);
 EXPORT_SYMBOL(netlink_set_nonroot);
 EXPORT_SYMBOL(netlink_unicast);
 EXPORT_SYMBOL(netlink_unregister_notifier);
-
+EXPORT_SYMBOL(nlmsg_notify);
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index 75bb47a898dd..d32599116c56 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -510,7 +510,7 @@ static int genl_ctrl_event(int event, void *data)
                 if (IS_ERR(msg))
                         return PTR_ERR(msg);
 
-                genlmsg_multicast(msg, 0, GENL_ID_CTRL);
+                genlmsg_multicast(msg, 0, GENL_ID_CTRL, GFP_KERNEL);
                 break;
         }