w1: add list masters w1 command

This patch series introduces and extends several userspace commands
used with netlink protocol.

Touch block command allows to write data and return sampled data to
the userspace.

Extended search and alarm seach commands to return list of slave
devices found during given search.

List masters command allows to send all registered master IDs to the
userspace.

Great thanks to Paul Alfille (owfs) who
tested this implementation and wrote w1-to-network daemon
http://sourceforge.net/projects/w1repeater/ and

Frederik Deweerdt and Randy Dunlap for review.

This patch:

Returns list of registered bus master devices.
Signed-off-by: Evgeniy Polyakov <zbr@ioremap.net>
Cc: Paul Alfille <paul.alfille@gmail.com>
Cc: Frederik Deweerdt <frederik.deweerdt@xprog.eu>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/w1/w1_netlink.c

@@ -128,6 +128,59 @@ static int w1_process_command_slave(struct w1_slave *sl, struct cn_msg *msg,
 	return err;
 }
 
+static int w1_process_command_root(struct cn_msg *msg, struct w1_netlink_msg *mcmd)
+{
+	struct w1_master *m;
+	struct cn_msg *cn;
+	struct w1_netlink_msg *w;
+	u32 *id;
+
+	if (mcmd->type != W1_LIST_MASTERS) {
+		printk(KERN_NOTICE "%s: msg: %x.%x, wrong type: %u, len: %u.\n",
+				__func__, msg->id.idx, msg->id.val, mcmd->type, mcmd->len);
+		return -EPROTO;
+	}
+
+	cn = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!cn)
+		return -ENOMEM;
+
+	cn->id.idx = CN_W1_IDX;
+	cn->id.val = CN_W1_VAL;
+
+	cn->seq = msg->seq;
+	cn->ack = 1;
+	cn->len = sizeof(struct w1_netlink_msg);
+	w = (struct w1_netlink_msg *)(cn + 1);
+
+	w->type = W1_LIST_MASTERS;
+	w->reserved = 0;
+	w->len = 0;
+	id = (u32 *)(w + 1);
+
+	mutex_lock(&w1_mlock);
+	list_for_each_entry(m, &w1_masters, w1_master_entry) {
+		if (cn->len + sizeof(*id) > PAGE_SIZE - sizeof(struct cn_msg)) {
+			cn_netlink_send(cn, 0, GFP_KERNEL);
+			cn->ack++;
+			cn->len = sizeof(struct w1_netlink_msg);
+			w->len = 0;
+			id = (u32 *)(w + 1);
+		}
+
+		*id = m->id;
+		w->len += sizeof(*id);
+		cn->len += sizeof(*id);
+		id++;
+	}
+	cn->ack = 0;
+	cn_netlink_send(cn, 0, GFP_KERNEL);
+	mutex_unlock(&w1_mlock);
+
+	kfree(cn);
+	return 0;
+}
+
 static void w1_cn_callback(void *data)
 {
 	struct cn_msg *msg = data;
@@ -164,6 +217,9 @@ static void w1_cn_callback(void *data)
 			sl = w1_search_slave(&id);
 			if (sl)
 				dev = sl->master;
+		} else {
+			err = w1_process_command_root(msg, m);
+			goto out_cont;
 		}
 
 		if (!dev) {

drivers/w1/w1_netlink.h

@@ -34,6 +34,7 @@ enum w1_netlink_message_types {
 	W1_MASTER_REMOVE,
 	W1_MASTER_CMD,
 	W1_SLAVE_CMD,
+	W1_LIST_MASTERS,
 };
 
 struct w1_netlink_msg