netdev - Re: [Patch net-next] sock_map: dump socket map id via diag

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Date:   Sun, 19 Feb 2023 12:21:39 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Cong Wang <cong.wang@...edance.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Sitnicki <jakub@...udflare.com>
Subject: Re: [Patch net-next] sock_map: dump socket map id via diag

On Sun, Feb 12, 2023 at 01:35:18PM +0200, Ido Schimmel wrote:
> On Sat, Feb 11, 2023 at 12:19:54PM -0800, Cong Wang wrote:
> > +int sock_map_idiag_dump(struct sock *sk, struct sk_buff *skb, int attrtype)
> > +{
> > +	struct sk_psock_link *link;
> > +	struct nlattr *nla, *attr;
> > +	int nr_links = 0, ret = 0;
> > +	struct sk_psock *psock;
> > +	u32 *ids;
> > +
> > +	rcu_read_lock();
> > +	psock = sk_psock_get(sk);
> > +	if (unlikely(!psock)) {
> > +		rcu_read_unlock();
> > +		return 0;
> > +	}
> > +
> > +	nla = nla_nest_start_noflag(skb, attrtype);
> 
> Since 'INET_DIAG_SOCKMAP' is a new attribute, did you consider using
> nla_nest_start() instead?

Yes, but other INET_DIAG_* attributes are not new, hence why ss.c still
uses parse_rtattr(), I am not sure whether it is okay to change it to
parse_rtattr_nested() just because of this.

> 
> > +	if (!nla) {
> > +		sk_psock_put(sk, psock);
> > +		rcu_read_unlock();
> > +		return -EMSGSIZE;
> > +	}
> > +	spin_lock_bh(&psock->link_lock);
> > +	list_for_each_entry(link, &psock->link, list)
> > +		nr_links++;
> > +
> > +	attr = nla_reserve(skb, SK_DIAG_BPF_SOCKMAP_MAP_ID,
> > +			   sizeof(link->map->id) * nr_links);
> > +	if (!attr) {
> > +		ret = -EMSGSIZE;
> > +		goto unlock;
> > +	}
> > +
> > +	ids = nla_data(attr);
> > +	list_for_each_entry(link, &psock->link, list) {
> > +		*ids = link->map->id;
> > +		ids++;
> > +	}
> 
> No strong preferences, but I think a more "modern" netlink usage would
> be to encode each ID in a separate u32 attribute rather than encoding an
> array of u32 in a single attribute. Example:
> 
> [ INET_DIAG_SOCKMAP ]	// nested
> 	[ SK_DIAG_BPF_SOCKMAP_MAP_ID ] // u32
> 	[ SK_DIAG_BPF_SOCKMAP_MAP_ID ] // u32
> 	...

How do we know how many ID's we have here? Note, INET_DIAG_SOCKMAP in
the future could have other attributes, so can't simply mark the end of
ID's.

> 
> Or:
> 
> [ INET_DIAG_SOCKMAP ]	// nested
> 	[ SK_DIAG_BPF_SOCKMAP_MAP_IDS ] // nested
> 		[ SK_DIAG_BPF_SOCKMAP_MAP_ID ] // u32
> 		[ SK_DIAG_BPF_SOCKMAP_MAP_ID ] // u32
> 		...

Yet one more nested level...

I prefer the current layout.

Thanks.