Re: [PATCH net-next 2/5] rtnetlink: Add netns_atomic flag in rtnl_link_ops

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Xiao Liang <shaw.leon@gmail.com>
Date: Wed, 23 Oct 2024 10:31:43 +0800
> Currently these two steps are needed to create a net device with
> IFLA_LINK_NETNSID attr:
> 
>  1. create and setup the netdev in the link netns with
>     rtnl_create_link()
>  2. move it to the target netns with dev_change_net_namespace()

IIRC, this is to send the notification in the link netns.


> 
> This has some side effects, including extra ifindex allocation, ifname
> validation and link notifications in link netns.
> 
> Add a netns_atomic flag, that if set to true, devices will be created in
> the target netns directly.
> 
> Signed-off-by: Xiao Liang <shaw.leon@gmail.com>
> ---
>  include/net/rtnetlink.h | 3 +++
>  net/core/rtnetlink.c    | 7 ++++---
>  2 files changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/include/net/rtnetlink.h b/include/net/rtnetlink.h
> index e0d9a8eae6b6..59594cef2272 100644
> --- a/include/net/rtnetlink.h
> +++ b/include/net/rtnetlink.h
> @@ -74,6 +74,8 @@ static inline int rtnl_msg_family(const struct nlmsghdr *nlh)
>   *	@srcu: Used internally
>   *	@kind: Identifier
>   *	@netns_refund: Physical device, move to init_net on netns exit
> + *	@netns_atomic: Device can be created in target netns even when
> + *		       link-netns is different, avoiding netns change.
>   *	@maxtype: Highest device specific netlink attribute number
>   *	@policy: Netlink policy for device specific attribute validation
>   *	@validate: Optional validation function for netlink/changelink parameters
> @@ -115,6 +117,7 @@ struct rtnl_link_ops {
>  	void			(*setup)(struct net_device *dev);
>  
>  	bool			netns_refund;
> +	bool			netns_atomic;
>  	unsigned int		maxtype;
>  	const struct nla_policy	*policy;
>  	int			(*validate)(struct nlattr *tb[],
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index ff8d25acfc00..99250779d8ba 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -3679,8 +3679,9 @@ static int rtnl_newlink_create(struct sk_buff *skb, struct ifinfomsg *ifm,
>  		name_assign_type = NET_NAME_ENUM;
>  	}
>  
> -	dev = rtnl_create_link(link_net ? : tgt_net, ifname,
> -			       name_assign_type, ops, tb, extack);
> +	dev = rtnl_create_link(!link_net || ops->netns_atomic ?
> +			       tgt_net : link_net, ifname, name_assign_type,
> +			       ops, tb, extack);
>  	if (IS_ERR(dev)) {
>  		err = PTR_ERR(dev);
>  		goto out;
> @@ -3700,7 +3701,7 @@ static int rtnl_newlink_create(struct sk_buff *skb, struct ifinfomsg *ifm,
>  	err = rtnl_configure_link(dev, ifm, portid, nlh);
>  	if (err < 0)
>  		goto out_unregister;
> -	if (link_net) {
> +	if (link_net && !ops->netns_atomic) {
>  		err = dev_change_net_namespace(dev, tgt_net, ifname);
>  		if (err < 0)
>  			goto out_unregister;
> -- 
> 2.47.0
>