Re: [PATCH net-next] rtnetlink: Honour NLM_F_ECHO flag in rtnl_{new, set}link

[Nicolas Dichtel <nicolas.dichtel@6wind.com>]

Le 21/09/2022 à 05:07, Hangbin Liu a écrit :
> Netlink messages are used for communicating between user and kernel space.
> When user space configures the kernel with netlink messages, it can set the
> NLM_F_ECHO flag to request the kernel to send the applied configuration back
> to the caller. This allows user space to retrieve configuration information
> that are filled by the kernel (either because these parameters can only be
> set by the kernel or because user space let the kernel choose a default
> value).
> 
> This patch handles NLM_F_ECHO flag and send link info back after
> rtnl_{new, set}link.
> 
> Suggested-by: Guillaume Nault <gnault@redhat.com>
> Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
> ---

[snip]

> @@ -3336,9 +3381,9 @@ static int rtnl_newlink_create(struct sk_buff *skb, struct ifinfomsg *ifm,
>  		return PTR_ERR(dest_net);
>  
>  	if (tb[IFLA_LINK_NETNSID]) {
> -		int id = nla_get_s32(tb[IFLA_LINK_NETNSID]);
> +		netnsid = nla_get_s32(tb[IFLA_LINK_NETNSID]);
>  
> -		link_net = get_net_ns_by_id(dest_net, id);
> +		link_net = get_net_ns_by_id(dest_net, netnsid);
>  		if (!link_net) {
>  			NL_SET_ERR_MSG(extack, "Unknown network namespace id");
>  			err =  -EINVAL;
> @@ -3382,6 +3427,17 @@ static int rtnl_newlink_create(struct sk_buff *skb, struct ifinfomsg *ifm,
>  		if (err)
>  			goto out_unregister;
>  	}
> +
> +	if (nlmsg_flags & NLM_F_ECHO) {
> +		u32 ext_filter_mask = 0;
> +
> +		if (tb[IFLA_EXT_MASK])
> +			ext_filter_mask = nla_get_u32(tb[IFLA_EXT_MASK]);
> +
> +		rtnl_echo_link_info(dev, NETLINK_CB(skb).portid, nlmsg_seq,
> +				    ext_filter_mask, netnsid);
=> netnsid, ie IFLA_LINK_NETNSID has nothing to do with IFLA_TARGET_NETNSID.
Link netns is used for x-netns interface like vlan for example. The vlan iface
could be in a netns while its lower iface could be in another netns.

The target netns is used when a netlink message is sent in a netns but should
act in another netns.

Regards,
Nicolas