Re: [PATCH net 1/2] net: advertise 'netns local' property via netlink

[Jakub Kicinski <kuba@kernel.org>]

On Thu,  6 Feb 2025 17:50:26 +0100 Nicolas Dichtel wrote:
> Since the below commit, there is no way to see if the netns_local property
> is set on a device. Let's add a netlink attribute to advertise it.

I think the motivation for the change may be worth elaborating on.
It's a bit unclear to me what user space would care about this
information, a bit of a "story" on how you hit the issue could
be useful perhaps? The uAPI is new but the stable tag indicates
regression..

> @@ -2041,6 +2042,7 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
>  		       netif_running(dev) ? READ_ONCE(dev->operstate) :
>  					    IF_OPER_DOWN) ||
>  	    nla_put_u8(skb, IFLA_LINKMODE, READ_ONCE(dev->link_mode)) ||
> +	    nla_put_u8(skb, IFLA_NETNS_LOCAL, dev->netns_local) ||

Maybe nla_put_flag() ? Or do you really care about false being there?
The 3 bytes wasted on padding always makes me question when people pick
NLA_u8.

>  	    nla_put_u32(skb, IFLA_MTU, READ_ONCE(dev->mtu)) ||
>  	    nla_put_u32(skb, IFLA_MIN_MTU, READ_ONCE(dev->min_mtu)) ||
>  	    nla_put_u32(skb, IFLA_MAX_MTU, READ_ONCE(dev->max_mtu)) ||