Merge branch 'net-store-netdevs-in-an-xarray'

Jakub Kicinski says:

====================
net: store netdevs in an xarray

One of more annoying developer experience gaps we have in netlink
is iterating over netdevs. It's painful. Add an xarray to make
it trivial.

v1: https://lore.kernel.org/all/20230722014237.4078962-1-kuba@kernel.org/
====================

Link: https://lore.kernel.org/r/20230726185530.2247698-1-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/netdevice.h

@@ -3016,6 +3016,9 @@ extern rwlock_t				dev_base_lock;		/* Device list lock */
 			if (netdev_master_upper_dev_get_rcu(slave) == (bond))
 #define net_device_entry(lh)	list_entry(lh, struct net_device, dev_list)
 
+#define for_each_netdev_dump(net, d, ifindex)				\
+	xa_for_each_start(&(net)->dev_by_index, (ifindex), (d), (ifindex))
+
 static inline struct net_device *next_net_device(struct net_device *dev)
 {
 	struct list_head *lh;

include/net/net_namespace.h

@@ -42,6 +42,7 @@
 #include <linux/idr.h>
 #include <linux/skbuff.h>
 #include <linux/notifier.h>
+#include <linux/xarray.h>
 
 struct user_namespace;
 struct proc_dir_entry;
@@ -69,7 +70,7 @@ struct net {
 	atomic_t		dev_unreg_count;
 
 	unsigned int		dev_base_seq;	/* protected by rtnl_mutex */
-	int			ifindex;
+	u32			ifindex;
 
 	spinlock_t		nsid_lock;
 	atomic_t		fnhe_genid;
@@ -110,6 +111,7 @@ struct net {
 
 	struct hlist_head 	*dev_name_head;
 	struct hlist_head	*dev_index_head;
+	struct xarray		dev_by_index;
 	struct raw_notifier_head	netdev_chain;
 
 	/* Note that @hash_mix can be read millions times per second,

net/core/dev.c

@@ -388,6 +388,8 @@ static void list_netdevice(struct net_device *dev)
 	hlist_add_head_rcu(&dev->index_hlist,
 			   dev_index_hash(net, dev->ifindex));
 	write_unlock(&dev_base_lock);
+	/* We reserved the ifindex, this can't fail */
+	WARN_ON(xa_store(&net->dev_by_index, dev->ifindex, dev, GFP_KERNEL));
 
 	dev_base_seq_inc(net);
 }
@@ -397,8 +399,12 @@ static void list_netdevice(struct net_device *dev)
  */
 static void unlist_netdevice(struct net_device *dev, bool lock)
 {
+	struct net *net = dev_net(dev);
+
 	ASSERT_RTNL();
 
+	xa_erase(&net->dev_by_index, dev->ifindex);
+
 	/* Unlink dev from the device chain */
 	if (lock)
 		write_lock(&dev_base_lock);
@@ -9565,23 +9571,35 @@ int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
 }
 
 /**
- *	dev_new_index	-	allocate an ifindex
+ * dev_index_reserve() - allocate an ifindex in a namespace
  * @net: the applicable net namespace
+ * @ifindex: requested ifindex, pass %0 to get one allocated
+ *
+ * Allocate a ifindex for a new device. Caller must either use the ifindex
+ * to store the device (via list_netdevice()) or call dev_index_release()
+ * to give the index up.
  *
- *	Returns a suitable unique value for a new device interface
- *	number.  The caller must hold the rtnl semaphore or the
- *	dev_base_lock to be sure it remains unique.
+ * Return: a suitable unique value for a new device interface number or -errno.
  */
-static int dev_new_index(struct net *net)
+static int dev_index_reserve(struct net *net, u32 ifindex)
 {
-	int ifindex = net->ifindex;
+	int err;
 
-	for (;;) {
-		if (++ifindex <= 0)
-			ifindex = 1;
-		if (!__dev_get_by_index(net, ifindex))
-			return net->ifindex = ifindex;
-	}
+	if (!ifindex)
+		err = xa_alloc_cyclic(&net->dev_by_index, &ifindex, NULL,
+				      xa_limit_31b, &net->ifindex, GFP_KERNEL);
+	else
+		err = xa_insert(&net->dev_by_index, ifindex, NULL, GFP_KERNEL);
+	if (err < 0)
+		return err;
+
+	return ifindex;
+}
+
+static void dev_index_release(struct net *net, int ifindex)
+{
+	/* Expect only unused indexes, unlist_netdevice() removes the used */
+	WARN_ON(xa_erase(&net->dev_by_index, ifindex));
 }
 
 /* Delayed registration/unregisteration */
@@ -10051,11 +10069,10 @@ int register_netdevice(struct net_device *dev)
 		goto err_uninit;
 	}
 
-	ret = -EBUSY;
-	if (!dev->ifindex)
-		dev->ifindex = dev_new_index(net);
-	else if (__dev_get_by_index(net, dev->ifindex))
+	ret = dev_index_reserve(net, dev->ifindex);
+	if (ret < 0)
 		goto err_uninit;
+	dev->ifindex = ret;
 
 	/* Transfer changeable features to wanted_features and enable
 	 * software offloads (GSO and GRO).
@@ -10102,7 +10119,7 @@ int register_netdevice(struct net_device *dev)
 	ret = call_netdevice_notifiers(NETDEV_POST_INIT, dev);
 	ret = notifier_to_errno(ret);
 	if (ret)
-		goto err_uninit;
+		goto err_ifindex_release;
 
 	ret = netdev_register_kobject(dev);
 	write_lock(&dev_base_lock);
@@ -10158,6 +10175,8 @@ int register_netdevice(struct net_device *dev)
 
 err_uninit_notify:
 	call_netdevice_notifiers(NETDEV_PRE_UNINIT, dev);
+err_ifindex_release:
+	dev_index_release(net, dev->ifindex);
 err_uninit:
 	if (dev->netdev_ops->ndo_uninit)
 		dev->netdev_ops->ndo_uninit(dev);
@@ -11035,9 +11054,19 @@ int __dev_change_net_namespace(struct net_device *dev, struct net *net,
 	}
 
 	/* Check that new_ifindex isn't used yet. */
-	err = -EBUSY;
-	if (new_ifindex && __dev_get_by_index(net, new_ifindex))
+	if (new_ifindex) {
+		err = dev_index_reserve(net, new_ifindex);
+		if (err < 0)
 			goto out;
+	} else {
+		/* If there is an ifindex conflict assign a new one */
+		err = dev_index_reserve(net, dev->ifindex);
+		if (err == -EBUSY)
+			err = dev_index_reserve(net, 0);
+		if (err < 0)
+			goto out;
+		new_ifindex = err;
+	}
 
 	/*
 	 * And now a mini version of register_netdevice unregister_netdevice.
@@ -11065,13 +11094,6 @@ int __dev_change_net_namespace(struct net_device *dev, struct net *net,
 	rcu_barrier();
 
 	new_nsid = peernet2id_alloc(dev_net(dev), net, GFP_KERNEL);
-	/* If there is an ifindex conflict assign a new one */
-	if (!new_ifindex) {
-		if (__dev_get_by_index(net, dev->ifindex))
-			new_ifindex = dev_new_index(net);
-		else
-			new_ifindex = dev->ifindex;
-	}
 
 	rtmsg_ifinfo_newnet(RTM_DELLINK, dev, ~0U, GFP_KERNEL, &new_nsid,
 			    new_ifindex);
@@ -11249,6 +11271,9 @@ static int __net_init netdev_init(struct net *net)
 	if (net->dev_index_head == NULL)
 		goto err_idx;
 
+	net->ifindex = 1;
+	xa_init_flags(&net->dev_by_index, XA_FLAGS_ALLOC);
+
 	RAW_INIT_NOTIFIER_HEAD(&net->netdev_chain);
 
 	return 0;
@@ -11346,6 +11371,7 @@ static void __net_exit netdev_exit(struct net *net)
 {
 	kfree(net->dev_name_head);
 	kfree(net->dev_index_head);
+	xa_destroy(&net->dev_by_index);
 	if (net != &init_net)
 		WARN_ON_ONCE(!list_empty(&net->dev_base_head));
 }

net/core/netdev-genl.c

@@ -101,43 +101,22 @@ int netdev_nl_dev_get_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
 {
 	struct net *net = sock_net(skb->sk);
 	struct net_device *netdev;
-	int idx = 0, s_idx;
-	int h, s_h;
-	int err;
-
-	s_h = cb->args[0];
-	s_idx = cb->args[1];
+	int err = 0;
 
 	rtnl_lock();
-
-	for (h = s_h; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {
-		struct hlist_head *head;
-
-		idx = 0;
-		head = &net->dev_index_head[h];
-		hlist_for_each_entry(netdev, head, index_hlist) {
-			if (idx < s_idx)
-				goto cont;
+	for_each_netdev_dump(net, netdev, cb->args[0]) {
 		err = netdev_nl_dev_fill(netdev, skb,
 					 NETLINK_CB(cb->skb).portid,
 					 cb->nlh->nlmsg_seq, 0,
 					 NETDEV_CMD_DEV_GET);
 		if (err < 0)
 			break;
-cont:
-			idx++;
 	}
-	}
-
 	rtnl_unlock();
 
 	if (err != -EMSGSIZE)
 		return err;
 
-	cb->args[1] = idx;
-	cb->args[0] = h;
-	cb->seq = net->dev_base_seq;
-
 	return skb->len;
 }
 

net/ethtool/netlink.c

@@ -252,8 +252,7 @@ int ethnl_multicast(struct sk_buff *skb, struct net_device *dev)
  * @ops:        request ops of currently processed message type
  * @req_info:   parsed request header of processed request
  * @reply_data: data needed to compose the reply
- * @pos_hash:   saved iteration position - hashbucket
- * @pos_idx:    saved iteration position - index
+ * @pos_ifindex: saved iteration position - ifindex
  *
  * These parameters are kept in struct netlink_callback as context preserved
  * between iterations. They are initialized by ethnl_default_start() and used
@@ -263,8 +262,7 @@ struct ethnl_dump_ctx {
 	const struct ethnl_request_ops	*ops;
 	struct ethnl_req_info		*req_info;
 	struct ethnl_reply_data		*reply_data;
-	int				pos_hash;
-	int				pos_idx;
+	unsigned long			pos_ifindex;
 };
 
 static const struct ethnl_request_ops *
@@ -490,55 +488,27 @@ static int ethnl_default_dumpit(struct sk_buff *skb,
 {
 	struct ethnl_dump_ctx *ctx = ethnl_dump_context(cb);
 	struct net *net = sock_net(skb->sk);
-	int s_idx = ctx->pos_idx;
-	int h, idx = 0;
+	struct net_device *dev;
 	int ret = 0;
 
 	rtnl_lock();
-	for (h = ctx->pos_hash; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {
-		struct hlist_head *head;
-		struct net_device *dev;
-		unsigned int seq;
-
-		head = &net->dev_index_head[h];
-
-restart_chain:
-		seq = net->dev_base_seq;
-		cb->seq = seq;
-		idx = 0;
-		hlist_for_each_entry(dev, head, index_hlist) {
-			if (idx < s_idx)
-				goto cont;
+	for_each_netdev_dump(net, dev, ctx->pos_ifindex) {
 		dev_hold(dev);
 		rtnl_unlock();
 
 		ret = ethnl_default_dump_one(skb, dev, ctx, cb);
+
+		rtnl_lock();
 		dev_put(dev);
-			if (ret < 0) {
-				if (ret == -EOPNOTSUPP)
-					goto lock_and_cont;
+
+		if (ret < 0 && ret != -EOPNOTSUPP) {
 			if (likely(skb->len))
 				ret = skb->len;
-				goto out;
-			}
-lock_and_cont:
-			rtnl_lock();
-			if (net->dev_base_seq != seq) {
-				s_idx = idx + 1;
-				goto restart_chain;
+			break;
 		}
-cont:
-			idx++;
-		}
-
 	}
 	rtnl_unlock();
 
-out:
-	ctx->pos_hash = h;
-	ctx->pos_idx = idx;
-	nl_dump_check_consistent(cb, nlmsg_hdr(skb));
-
 	return ret;
 }
 
@@ -584,8 +554,7 @@ static int ethnl_default_start(struct netlink_callback *cb)
 	ctx->ops = ops;
 	ctx->req_info = req_info;
 	ctx->reply_data = reply_data;
-	ctx->pos_hash = 0;
-	ctx->pos_idx = 0;
+	ctx->pos_ifindex = 0;
 
 	return 0;
 

net/ethtool/tunnels.c

@@ -212,8 +212,7 @@ int ethnl_tunnel_info_doit(struct sk_buff *skb, struct genl_info *info)
 
 struct ethnl_tunnel_info_dump_ctx {
 	struct ethnl_req_info	req_info;
-	int			pos_hash;
-	int			pos_idx;
+	unsigned long		ifindex;
 };
 
 int ethnl_tunnel_info_start(struct netlink_callback *cb)
@@ -243,34 +242,24 @@ int ethnl_tunnel_info_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
 {
 	struct ethnl_tunnel_info_dump_ctx *ctx = (void *)cb->ctx;
 	struct net *net = sock_net(skb->sk);
-	int s_idx = ctx->pos_idx;
-	int h, idx = 0;
+	struct net_device *dev;
 	int ret = 0;
 	void *ehdr;
 
 	rtnl_lock();
-	cb->seq = net->dev_base_seq;
-	for (h = ctx->pos_hash; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {
-		struct hlist_head *head;
-		struct net_device *dev;
-
-		head = &net->dev_index_head[h];
-		idx = 0;
-		hlist_for_each_entry(dev, head, index_hlist) {
-			if (idx < s_idx)
-				goto cont;
-
+	for_each_netdev_dump(net, dev, ctx->ifindex) {
 		ehdr = ethnl_dump_put(skb, cb,
 				      ETHTOOL_MSG_TUNNEL_INFO_GET_REPLY);
 		if (!ehdr) {
 			ret = -EMSGSIZE;
-				goto out;
+			break;
 		}
 
-			ret = ethnl_fill_reply_header(skb, dev, ETHTOOL_A_TUNNEL_INFO_HEADER);
+		ret = ethnl_fill_reply_header(skb, dev,
+					      ETHTOOL_A_TUNNEL_INFO_HEADER);
 		if (ret < 0) {
 			genlmsg_cancel(skb, ehdr);
-				goto out;
+			break;
 		}
 
 		ctx->req_info.dev = dev;
@@ -279,21 +268,13 @@ int ethnl_tunnel_info_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
 		if (ret < 0) {
 			genlmsg_cancel(skb, ehdr);
 			if (ret == -EOPNOTSUPP)
-					goto cont;
-				goto out;
+				continue;
+			break;
 		}
 		genlmsg_end(skb, ehdr);
-cont:
-			idx++;
 	}
-	}
-out:
 	rtnl_unlock();
 
-	ctx->pos_hash = h;
-	ctx->pos_idx = idx;
-	nl_dump_check_consistent(cb, nlmsg_hdr(skb));
-
 	if (ret == -EMSGSIZE && skb->len)
 		return skb->len;
 	return ret;