brcompat: Refactor infrastructure for communication with ovs-brcompatd.

In an upcoming change, brcompat will need to receive bulk data from
ovs-brcompatd.  The existing brcompat infrastructure for receiving data
only supports returning an error code, so this commit adds the ability to
receive an arbitrary sk_buff and updates the existing users to handle it.

datapath/brcompat.c

@@ -40,10 +40,11 @@ static DEFINE_MUTEX(brc_serial);
 /* Userspace communication. */
 static DEFINE_SPINLOCK(brc_lock);    /* Ensure atomic access to these vars. */
 static DECLARE_COMPLETION(brc_done); /* Userspace signaled operation done? */
-static int brc_err;		     /* Error code from userspace. */
+static struct sk_buff *brc_reply;    /* Reply from userspace. */
 static u32 brc_seq;		     /* Sequence number for current op. */
 
-static int brc_send_command(const char *bridge, const char *port, int op);
+static struct sk_buff *brc_send_command(struct sk_buff *, struct nlattr **attrs);
+static int brc_send_simple_command(struct sk_buff *);
 
 static int
 get_dp_ifindices(int *indices, int num)
@@ -75,16 +76,55 @@ get_port_ifindices(struct datapath *dp, int *ifindices, int num)
 	rcu_read_unlock();
 }
 
+static struct sk_buff *
+brc_make_request(int op, const char *bridge, const char *port)
+{
+	struct sk_buff *skb = genlmsg_new(NLMSG_GOODSIZE, GFP_KERNEL);
+	if (!skb)
+		goto error;
+
+	genlmsg_put(skb, 0, 0, &brc_genl_family, 0, op);
+	NLA_PUT_STRING(skb, BRC_GENL_A_DP_NAME, bridge);
+	if (port)
+		NLA_PUT_STRING(skb, BRC_GENL_A_PORT_NAME, port);
+	return skb;
+
+nla_put_failure:
+	kfree_skb(skb);
+error:
+	return NULL;
+}
+
+static int brc_send_simple_command(struct sk_buff *request)
+{
+	struct nlattr *attrs[BRC_GENL_A_MAX + 1];
+	struct sk_buff *reply;
+	int error;
+
+	reply = brc_send_command(request, attrs);
+	if (IS_ERR(reply))
+		return PTR_ERR(reply);
+
+	error = nla_get_u32(attrs[BRC_GENL_A_ERR_CODE]);
+	kfree_skb(reply);
+	return -error;
+}
+
 static int brc_add_del_bridge(char __user *uname, int add)
 {
+	struct sk_buff *request;
 	char name[IFNAMSIZ];
 
 	if (copy_from_user(name, uname, IFNAMSIZ))
 		return -EFAULT;
 
 	name[IFNAMSIZ - 1] = 0;
-	return brc_send_command(name, NULL,
+	request = brc_make_request(add ? BRC_GENL_C_DP_ADD : BRC_GENL_C_DP_DEL,
-				add ? BRC_GENL_C_DP_ADD : BRC_GENL_C_DP_DEL);
+				   name, NULL);
+	if (!request)
+		return -ENOMEM;
+
+	return brc_send_simple_command(request);
 }
 
 static int brc_get_bridges(int __user *uindices, int n)
@@ -154,8 +194,8 @@ brc_ioctl_deviceless_stub(struct net *net, unsigned int cmd, void __user *uarg)
 static int
 brc_add_del_port(struct net_device *dev, int port_ifindex, int add)
 {
+	struct sk_buff *request;
 	struct net_device *port;
-	char dev_name[IFNAMSIZ], port_name[IFNAMSIZ];
 	int err;
 
 	port = __dev_get_by_index(&init_net, port_ifindex);
@@ -163,13 +203,14 @@ brc_add_del_port(struct net_device *dev, int port_ifindex, int add)
 		return -EINVAL;
 
 	/* Save name of dev and port because there's a race between the
-	 * rtnl_unlock() and the brc_send_command(). */
+	 * rtnl_unlock() and the brc_send_simple_command(). */
-	strcpy(dev_name, dev->name);
+	request = brc_make_request(add ? BRC_GENL_C_PORT_ADD : BRC_GENL_C_PORT_DEL,
-	strcpy(port_name, port->name);
+				   dev->name, port->name);
+	if (!request)
+		return -ENOMEM;
 
 	rtnl_unlock();
-	err = brc_send_command(dev_name, port_name,
+	err = brc_send_simple_command(request);
-			       add ? BRC_GENL_C_PORT_ADD : BRC_GENL_C_PORT_DEL);
 	rtnl_lock();
 
 	return err;
@@ -330,12 +371,22 @@ brc_genl_dp_result(struct sk_buff *skb, struct genl_info *info)
 	if (!info->attrs[BRC_GENL_A_ERR_CODE])
 		return -EINVAL;
 
+	skb = skb_clone(skb, GFP_KERNEL);
+	if (!skb)
+		return -ENOMEM;
+
 	spin_lock_irqsave(&brc_lock, flags);
 	if (brc_seq == info->snd_seq) {
-		brc_err = nla_get_u32(info->attrs[BRC_GENL_A_ERR_CODE]);
+		brc_seq++;
+
+		if (brc_reply)
+			kfree_skb(brc_reply);
+		brc_reply = skb;
+
 		complete(&brc_done);
 		err = 0;
 	} else {
+		kfree_skb(skb);
 		err = -ESTALE;
 	}
 	spin_unlock_irqrestore(&brc_lock, flags);
@@ -359,11 +410,10 @@ static struct genl_ops brc_genl_ops_set_proc = {
 	.dumpit = NULL
 };
 
-static int brc_send_command(const char *bridge, const char *port, int op)
+static struct sk_buff *brc_send_command(struct sk_buff *request, struct nlattr **attrs)
 {
 	unsigned long int flags;
-	struct sk_buff *skb;
+	struct sk_buff *reply;
-	void *data;
 	int error;
 
 	mutex_lock(&brc_serial);
@@ -371,41 +421,41 @@ static int brc_send_command(const char *bridge, const char *port, int op)
 	/* Increment sequence number first, so that we ignore any replies
 	 * to stale requests. */
 	spin_lock_irqsave(&brc_lock, flags);
-	brc_seq++;
+	nlmsg_hdr(request)->nlmsg_seq = ++brc_seq;
 	INIT_COMPLETION(brc_done);
 	spin_unlock_irqrestore(&brc_lock, flags);
 
-	/* Compose message. */
+	nlmsg_end(request, nlmsg_hdr(request));
-	skb = genlmsg_new(NLMSG_GOODSIZE, GFP_KERNEL);
-	error = -ENOMEM;
-	if (skb == NULL)
-		goto exit_unlock;
-	data = genlmsg_put(skb, 0, brc_seq, &brc_genl_family, 0, op);
-
-	NLA_PUT_STRING(skb, BRC_GENL_A_DP_NAME, bridge);
-	if (port)
-		NLA_PUT_STRING(skb, BRC_GENL_A_PORT_NAME, port);
-
-	genlmsg_end(skb, data);
 
 	/* Send message. */
-	error = genlmsg_multicast(skb, 0, brc_mc_group.id, GFP_KERNEL);
+	error = genlmsg_multicast(request, 0, brc_mc_group.id, GFP_KERNEL);
 	if (error < 0)
-		goto exit_unlock;
+		goto error;
 
 	/* Wait for reply. */
 	error = -ETIMEDOUT;
 	if (!wait_for_completion_timeout(&brc_done, BRC_TIMEOUT))
-		goto exit_unlock;
+		goto error;
 
-	error = -brc_err;
+	/* Grab reply. */
-	goto exit_unlock;
+	spin_lock_irqsave(&brc_lock, flags);
+	reply = brc_reply;
+	brc_reply = NULL;
+	spin_unlock_irqrestore(&brc_lock, flags);
 
-nla_put_failure:
-	kfree_skb(skb);
-exit_unlock:
 	mutex_unlock(&brc_serial);
-	return error;
+
+	/* Re-parse message.  Can't fail, since it parsed correctly once
+	 * already. */
+	error = nlmsg_parse(nlmsg_hdr(reply), GENL_HDRLEN,
+			    attrs, BRC_GENL_A_MAX, brc_genl_policy);
+	WARN_ON(error);
+
+	return reply;
+
+error:
+	mutex_unlock(&brc_serial);
+	return ERR_PTR(error);
 }
 
 int brc_add_dp(struct datapath *dp)