rtnetlink: Pack newlink() params into struct

There are 4 net namespaces involved when creating links:

 - source netns - where the netlink socket resides,
 - target netns - where to put the device being created,
 - link netns - netns associated with the device (backend),
 - peer netns - netns of peer device.

Currently, two nets are passed to newlink() callback - "src_net"
parameter and "dev_net" (implicitly in net_device). They are set as
follows, depending on netlink attributes in the request.

 +------------+-------------------+---------+---------+
 | peer netns | IFLA_LINK_NETNSID | src_net | dev_net |
 +------------+-------------------+---------+---------+
 |            | absent            | source  | target  |
 | absent     +-------------------+---------+---------+
 |            | present           | link    | link    |
 +------------+-------------------+---------+---------+
 |            | absent            | peer    | target  |
 | present    +-------------------+---------+---------+
 |            | present           | peer    | link    |
 +------------+-------------------+---------+---------+

When IFLA_LINK_NETNSID is present, the device is created in link netns
first and then moved to target netns. This has some side effects,
including extra ifindex allocation, ifname validation and link events.
These could be avoided if we create it in target netns from
the beginning.

On the other hand, the meaning of src_net parameter is ambiguous. It
varies depending on how parameters are passed. It is the effective
link (or peer netns) by design, but some drivers ignore it and use
dev_net instead.

To provide more netns context for drivers, this patch packs existing
newlink() parameters, along with the source netns, link netns and peer
netns, into a struct. The old "src_net" is renamed to "net" to avoid
confusion with real source netns, and will be deprecated later. The use
of src_net are converted to params->net trivially.

Signed-off-by: Xiao Liang <shaw.leon@gmail.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250219125039.18024-3-shaw.leon@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 25 insertions, 6 deletions

diff --git a/include/linux/if_macvlan.h b/include/linux/if_macvlan.h
index 523025106a64..0f7281e3e448 100644
--- a/include/linux/if_macvlan.h
+++ b/include/linux/if_macvlan.h
@@ -59,8 +59,10 @@ static inline void macvlan_count_rx(const struct macvlan_dev *vlan,
 
 extern void macvlan_common_setup(struct net_device *dev);
 
-extern int macvlan_common_newlink(struct net *src_net, struct net_device *dev,
-				  struct nlattr *tb[], struct nlattr *data[],
+struct rtnl_newlink_params;
+
+extern int macvlan_common_newlink(struct net_device *dev,
+				  struct rtnl_newlink_params *params,
 				  struct netlink_ext_ack *extack);
 
 extern void macvlan_dellink(struct net_device *dev, struct list_head *head);
diff --git a/include/net/rtnetlink.h b/include/net/rtnetlink.h
index bc0069a8b6ea..563a6a27436c 100644
--- a/include/net/rtnetlink.h
+++ b/include/net/rtnetlink.h
@@ -70,6 +70,25 @@ static inline int rtnl_msg_family(const struct nlmsghdr *nlh)
 }
 
 /**
+ * struct rtnl_newlink_params - parameters of rtnl_link_ops::newlink()
+ *
+ * @net: Netns of interest
+ * @src_net: Source netns of rtnetlink socket
+ * @link_net: Link netns by IFLA_LINK_NETNSID, NULL if not specified
+ * @peer_net: Peer netns
+ * @tb: IFLA_* attributes
+ * @data: IFLA_INFO_DATA attributes
+ */
+struct rtnl_newlink_params {
+	struct net *net;
+	struct net *src_net;
+	struct net *link_net;
+	struct net *peer_net;
+	struct nlattr **tb;
+	struct nlattr **data;
+};
+
+/**
  *	struct rtnl_link_ops - rtnetlink link operations
  *
  *	@list: Used internally, protected by link_ops_mutex and SRCU
@@ -125,10 +144,8 @@ struct rtnl_link_ops {
 					    struct nlattr *data[],
 					    struct netlink_ext_ack *extack);
 
-	int			(*newlink)(struct net *src_net,
-					   struct net_device *dev,
-					   struct nlattr *tb[],
-					   struct nlattr *data[],
+	int			(*newlink)(struct net_device *dev,
+					   struct rtnl_newlink_params *params,
 					   struct netlink_ext_ack *extack);
 	int			(*changelink)(struct net_device *dev,
 					      struct nlattr *tb[],