[NET]: Add netlink connector.

Kernel connector - new userspace <-> kernel space easy to use
communication module which implements easy to use bidirectional
message bus using netlink as it's backend.  Connector was created to
eliminate complex skb handling both in send and receive message bus
direction.

Connector driver adds possibility to connect various agents using as
one of it's backends netlink based network.  One must register
callback and identifier. When driver receives special netlink message
with appropriate identifier, appropriate callback will be called.

From the userspace point of view it's quite straightforward:

	socket();
	bind();
	send();
	recv();

But if kernelspace want to use full power of such connections, driver
writer must create special sockets, must know about struct sk_buff
handling...  Connector allows any kernelspace agents to use netlink
based networking for inter-process communication in a significantly
easier way:

int cn_add_callback(struct cb_id *id, char *name, void (*callback) (void *));
void cn_netlink_send(struct cn_msg *msg, u32 __groups, int gfp_mask);

struct cb_id
{
	__u32			idx;
	__u32			val;
};

idx and val are unique identifiers which must be registered in
connector.h for in-kernel usage.  void (*callback) (void *) - is a
callback function which will be called when message with above idx.val
will be received by connector core.

Using connector completely hides low-level transport layer from it's
users.

Connector uses new netlink ability to have many groups in one socket.

[ Incorporating many cleanups and fixes by myself and
  Andrew Morton -DaveM ]

Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 327 insertions, 0 deletions

diff --git a/Documentation/connector/cn_test.c b/Documentation/connector/cn_test.c
new file mode 100644
index 000000000000..b7de82e9c0e0
--- /dev/null
+++ b/Documentation/connector/cn_test.c
@@ -0,0 +1,194 @@
+/*
+ * 	cn_test.c
+ * 
+ * 2004-2005 Copyright (c) Evgeniy Polyakov <johnpol@2ka.mipt.ru>
+ * All rights reserved.
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/skbuff.h>
+#include <linux/timer.h>
+
+#include "connector.h"
+
+static struct cb_id cn_test_id = { 0x123, 0x456 };
+static char cn_test_name[] = "cn_test";
+static struct sock *nls;
+static struct timer_list cn_test_timer;
+
+void cn_test_callback(void *data)
+{
+	struct cn_msg *msg = (struct cn_msg *)data;
+
+	printk("%s: %lu: idx=%x, val=%x, seq=%u, ack=%u, len=%d: %s.\n",
+	       __func__, jiffies, msg->id.idx, msg->id.val,
+	       msg->seq, msg->ack, msg->len, (char *)msg->data);
+}
+
+static int cn_test_want_notify(void)
+{
+	struct cn_ctl_msg *ctl;
+	struct cn_notify_req *req;
+	struct cn_msg *msg = NULL;
+	int size, size0;
+	struct sk_buff *skb;
+	struct nlmsghdr *nlh;
+	u32 group = 1;
+
+	size0 = sizeof(*msg) + sizeof(*ctl) + 3 * sizeof(*req);
+
+	size = NLMSG_SPACE(size0);
+
+	skb = alloc_skb(size, GFP_ATOMIC);
+	if (!skb) {
+		printk(KERN_ERR "Failed to allocate new skb with size=%u.\n",
+		       size);
+
+		return -ENOMEM;
+	}
+
+	nlh = NLMSG_PUT(skb, 0, 0x123, NLMSG_DONE, size - sizeof(*nlh));
+
+	msg = (struct cn_msg *)NLMSG_DATA(nlh);
+
+	memset(msg, 0, size0);
+
+	msg->id.idx = -1;
+	msg->id.val = -1;
+	msg->seq = 0x123;
+	msg->ack = 0x345;
+	msg->len = size0 - sizeof(*msg);
+
+	ctl = (struct cn_ctl_msg *)(msg + 1);
+
+	ctl->idx_notify_num = 1;
+	ctl->val_notify_num = 2;
+	ctl->group = group;
+	ctl->len = msg->len - sizeof(*ctl);
+
+	req = (struct cn_notify_req *)(ctl + 1);
+
+	/*
+	 * Idx.
+	 */
+	req->first = cn_test_id.idx;
+	req->range = 10;
+
+	/*
+	 * Val 0.
+	 */
+	req++;
+	req->first = cn_test_id.val;
+	req->range = 10;
+
+	/*
+	 * Val 1.
+	 */
+	req++;
+	req->first = cn_test_id.val + 20;
+	req->range = 10;
+
+	NETLINK_CB(skb).dst_groups = ctl->group;
+	//netlink_broadcast(nls, skb, 0, ctl->group, GFP_ATOMIC);
+	netlink_unicast(nls, skb, 0, 0);
+
+	printk(KERN_INFO "Request was sent. Group=0x%x.\n", ctl->group);
+
+	return 0;
+
+nlmsg_failure:
+	printk(KERN_ERR "Failed to send %u.%u\n", msg->seq, msg->ack);
+	kfree_skb(skb);
+	return -EINVAL;
+}
+
+static u32 cn_test_timer_counter;
+static void cn_test_timer_func(unsigned long __data)
+{
+	struct cn_msg *m;
+	char data[32];
+
+	m = kmalloc(sizeof(*m) + sizeof(data), GFP_ATOMIC);
+	if (m) {
+		memset(m, 0, sizeof(*m) + sizeof(data));
+
+		memcpy(&m->id, &cn_test_id, sizeof(m->id));
+		m->seq = cn_test_timer_counter;
+		m->len = sizeof(data);
+
+		m->len =
+		    scnprintf(data, sizeof(data), "counter = %u",
+			      cn_test_timer_counter) + 1;
+
+		memcpy(m + 1, data, m->len);
+
+		cn_netlink_send(m, 0, gfp_any());
+		kfree(m);
+	}
+
+	cn_test_timer_counter++;
+
+	mod_timer(&cn_test_timer, jiffies + HZ);
+}
+
+static int cn_test_init(void)
+{
+	int err;
+
+	err = cn_add_callback(&cn_test_id, cn_test_name, cn_test_callback);
+	if (err)
+		goto err_out;
+	cn_test_id.val++;
+	err = cn_add_callback(&cn_test_id, cn_test_name, cn_test_callback);
+	if (err) {
+		cn_del_callback(&cn_test_id);
+		goto err_out;
+	}
+
+	init_timer(&cn_test_timer);
+	cn_test_timer.function = cn_test_timer_func;
+	cn_test_timer.expires = jiffies + HZ;
+	cn_test_timer.data = 0;
+	add_timer(&cn_test_timer);
+
+	return 0;
+
+      err_out:
+	if (nls && nls->sk_socket)
+		sock_release(nls->sk_socket);
+
+	return err;
+}
+
+static void cn_test_fini(void)
+{
+	del_timer_sync(&cn_test_timer);
+	cn_del_callback(&cn_test_id);
+	cn_test_id.val--;
+	cn_del_callback(&cn_test_id);
+	if (nls && nls->sk_socket)
+		sock_release(nls->sk_socket);
+}
+
+module_init(cn_test_init);
+module_exit(cn_test_fini);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Evgeniy Polyakov <johnpol@2ka.mipt.ru>");
+MODULE_DESCRIPTION("Connector's test module");
diff --git a/Documentation/connector/connector.txt b/Documentation/connector/connector.txt
new file mode 100644
index 000000000000..54a0a14bfbe3
--- /dev/null
+++ b/Documentation/connector/connector.txt
@@ -0,0 +1,133 @@
+/*****************************************/
+Kernel Connector.
+/*****************************************/
+
+Kernel connector - new netlink based userspace <-> kernel space easy
+to use communication module.
+
+Connector driver adds possibility to connect various agents using
+netlink based network.  One must register callback and
+identifier. When driver receives special netlink message with
+appropriate identifier, appropriate callback will be called.
+
+From the userspace point of view it's quite straightforward:
+
+	socket();
+	bind();
+	send();
+	recv();
+
+But if kernelspace want to use full power of such connections, driver
+writer must create special sockets, must know about struct sk_buff
+handling...  Connector allows any kernelspace agents to use netlink
+based networking for inter-process communication in a significantly
+easier way:
+
+int cn_add_callback(struct cb_id *id, char *name, void (*callback) (void *));
+void cn_netlink_send(struct cn_msg *msg, u32 __group, int gfp_mask);
+
+struct cb_id
+{
+	__u32			idx;
+	__u32			val;
+};
+
+idx and val are unique identifiers which must be registered in
+connector.h for in-kernel usage.  void (*callback) (void *) - is a
+callback function which will be called when message with above idx.val
+will be received by connector core.  Argument for that function must
+be dereferenced to struct cn_msg *.
+
+struct cn_msg
+{
+	struct cb_id 		id;
+
+	__u32			seq;
+	__u32			ack;
+
+	__u32			len;		/* Length of the following data */
+	__u8			data[0];
+};
+
+/*****************************************/
+Connector interfaces.
+/*****************************************/
+
+int cn_add_callback(struct cb_id *id, char *name, void (*callback) (void *));
+
+Registers new callback with connector core.
+
+struct cb_id *id 		- unique connector's user identifier.
+			  	  It must be registered in connector.h for legal in-kernel users.
+char *name 			- connector's callback symbolic name.
+void (*callback) (void *)	- connector's callback.
+				  Argument must be dereferenced to struct cn_msg *.
+
+void cn_del_callback(struct cb_id *id);
+
+Unregisters new callback with connector core.
+
+struct cb_id *id 		- unique connector's user identifier.
+
+void cn_netlink_send(struct cn_msg *msg, u32 __groups, int gfp_mask);
+
+Sends message to the specified groups.  It can be safely called from
+any context, but may silently fail under strong memory pressure.
+
+struct cn_msg *			- message header(with attached data).
+u32 __group			- destination group.
+				  If __group is zero, then appropriate group will
+				  be searched through all registered connector users,
+				  and message will be delivered to the group which was
+				  created for user with the same ID as in msg.
+				  If __group is not zero, then message will be delivered
+				  to the specified group.
+int gfp_mask			- GFP mask.
+
+Note: When registering new callback user, connector core assigns
+netlink group to the user which is equal to it's id.idx.
+
+/*****************************************/
+Protocol description.
+/*****************************************/
+
+Current offers transport layer with fixed header.  Recommended
+protocol which uses such header is following:
+
+msg->seq and msg->ack are used to determine message genealogy.  When
+someone sends message it puts there locally unique sequence and random
+acknowledge numbers.  Sequence number may be copied into
+nlmsghdr->nlmsg_seq too.
+
+Sequence number is incremented with each message to be sent.
+
+If we expect reply to our message, then sequence number in received
+message MUST be the same as in original message, and acknowledge
+number MUST be the same + 1.
+
+If we receive message and it's sequence number is not equal to one we
+are expecting, then it is new message.  If we receive message and it's
+sequence number is the same as one we are expecting, but it's
+acknowledge is not equal acknowledge number in original message + 1,
+then it is new message.
+
+Obviously, protocol header contains above id.
+
+connector allows event notification in the following form: kernel
+driver or userspace process can ask connector to notify it when
+selected id's will be turned on or off(registered or unregistered it's
+callback). It is done by sending special command to connector
+driver(it also registers itself with id={-1, -1}).
+
+As example of usage Documentation/connector now contains cn_test.c -
+testing module which uses connector to request notification and to
+send messages.
+
+/*****************************************/
+Reliability.
+/*****************************************/
+
+Netlink itself is not reliable protocol, that means that messages can
+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.