[NETLINK]: Generic netlink receive queue processor

Introduces netlink_run_queue() to handle the receive queue of
a netlink socket in a generic way. Processes as much as there
was in the queue upon entry and invokes a callback function
for each netlink message found. The callback function may
refuse a message by returning a negative error code but setting
the error pointer to 0 in which case netlink_run_queue() will
return with a qlen != 0.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/netlink.h

@@ -183,6 +183,12 @@ struct nla_policy {
 	u16		minlen;
 };
 
+extern void		netlink_run_queue(struct sock *sk, unsigned int *qlen,
+					  int (*cb)(struct sk_buff *,
+						    struct nlmsghdr *, int *));
+extern void		netlink_queue_skip(struct nlmsghdr *nlh,
+					   struct sk_buff *skb);
+
 extern int		nla_validate(struct nlattr *head, int len, int maxtype,
 				     struct nla_policy *policy);
 extern int		nla_parse(struct nlattr *tb[], int maxtype,

net/netlink/af_netlink.c

@@ -58,6 +58,7 @@
 
 #include <net/sock.h>
 #include <net/scm.h>
+#include <net/netlink.h>
 
 #define Nprintk(a...)
 #define NLGRPSZ(x)	(ALIGN(x, sizeof(unsigned long) * 8) / 8)
@@ -1411,6 +1412,94 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err)
 	netlink_unicast(in_skb->sk, skb, NETLINK_CB(in_skb).pid, MSG_DONTWAIT);
 }
 
+static int netlink_rcv_skb(struct sk_buff *skb, int (*cb)(struct sk_buff *,
+						     struct nlmsghdr *, int *))
+{
+	unsigned int total_len;
+	struct nlmsghdr *nlh;
+	int err;
+
+	while (skb->len >= nlmsg_total_size(0)) {
+		nlh = (struct nlmsghdr *) skb->data;
+
+		if (skb->len < nlh->nlmsg_len)
+			return 0;
+
+		total_len = min(NLMSG_ALIGN(nlh->nlmsg_len), skb->len);
+
+		if (cb(skb, nlh, &err) < 0) {
+			/* Not an error, but we have to interrupt processing
+			 * here. Note: that in this case we do not pull
+			 * message from skb, it will be processed later.
+			 */
+			if (err == 0)
+				return -1;
+			netlink_ack(skb, nlh, err);
+		} else if (nlh->nlmsg_flags & NLM_F_ACK)
+			netlink_ack(skb, nlh, 0);
+
+		skb_pull(skb, total_len);
+	}
+
+	return 0;
+}
+
+/**
+ * nelink_run_queue - Process netlink receive queue.
+ * @sk: Netlink socket containing the queue
+ * @qlen: Place to store queue length upon entry
+ * @cb: Callback function invoked for each netlink message found
+ *
+ * Processes as much as there was in the queue upon entry and invokes
+ * a callback function for each netlink message found. The callback
+ * function may refuse a message by returning a negative error code
+ * but setting the error pointer to 0 in which case this function
+ * returns with a qlen != 0.
+ *
+ * qlen must be initialized to 0 before the initial entry, afterwards
+ * the function may be called repeatedly until qlen reaches 0.
+ */
+void netlink_run_queue(struct sock *sk, unsigned int *qlen,
+		       int (*cb)(struct sk_buff *, struct nlmsghdr *, int *))
+{
+	struct sk_buff *skb;
+
+	if (!*qlen || *qlen > skb_queue_len(&sk->sk_receive_queue))
+		*qlen = skb_queue_len(&sk->sk_receive_queue);
+
+	for (; *qlen; (*qlen)--) {
+		skb = skb_dequeue(&sk->sk_receive_queue);
+		if (netlink_rcv_skb(skb, cb)) {
+			if (skb->len)
+				skb_queue_head(&sk->sk_receive_queue, skb);
+			else {
+				kfree_skb(skb);
+				(*qlen)--;
+			}
+			break;
+		}
+
+		kfree_skb(skb);
+	}
+}
+
+/**
+ * netlink_queue_skip - Skip netlink message while processing queue.
+ * @nlh: Netlink message to be skipped
+ * @skb: Socket buffer containing the netlink messages.
+ *
+ * Pulls the given netlink message off the socket buffer so the next
+ * call to netlink_queue_run() will not reconsider the message.
+ */
+void netlink_queue_skip(struct nlmsghdr *nlh, struct sk_buff *skb)
+{
+	int msglen = NLMSG_ALIGN(nlh->nlmsg_len);
+
+	if (msglen > skb->len)
+		msglen = skb->len;
+
+	skb_pull(skb, msglen);
+}
 
 #ifdef CONFIG_PROC_FS
 struct nl_seq_iter {
@@ -1659,6 +1748,8 @@ static int __init netlink_proto_init(void)
 core_initcall(netlink_proto_init);
 
 EXPORT_SYMBOL(netlink_ack);
+EXPORT_SYMBOL(netlink_run_queue);
+EXPORT_SYMBOL(netlink_queue_skip);
 EXPORT_SYMBOL(netlink_broadcast);
 EXPORT_SYMBOL(netlink_dump_start);
 EXPORT_SYMBOL(netlink_kernel_create);