RE: [Patch net-next v2] sock_map: dump socket map id via diag

[John Fastabend <john.fastabend@gmail.com>]

Cong Wang wrote:
> From: Cong Wang <cong.wang@bytedance.com>
> 
> Currently there is no way to know which sockmap a socket has been added
> to from outside, especially for that a socket can be added to multiple
> sockmap's. We could dump this via socket diag, as shown below.
> 
> Sample output:
> 
>   # ./iproute2/misc/ss -tnaie --sockmap
>   ESTAB  0      344329     127.0.0.1:1234     127.0.0.1:40912 ino:21098 sk:5 cgroup:/user.slice/user-0.slice/session-c1.scope <-> sockmap: 1
> 
>   # bpftool map
>   1: sockmap  flags 0x0
>   	key 4B  value 4B  max_entries 2  memlock 4096B
> 	pids echo-sockmap(549)
>   4: array  name pid_iter.rodata  flags 0x480
> 	key 4B  value 4B  max_entries 1  memlock 4096B
> 	btf_id 10  frozen
> 	pids bpftool(624)
> 
> In the future, we could dump other sockmap related stats too, hence I
> make it a nested attribute.
> 
> Cc: John Fastabend <john.fastabend@gmail.com>
> Cc: Jakub Sitnicki <jakub@cloudflare.com>
> Signed-off-by: Cong Wang <cong.wang@bytedance.com>
> ---
> v2: rename enum's with more generic names
>     sock_map_idiag_dump -> sock_map_diag_dump()
>     make sock_map_diag_dump() return number of maps
> 
>  include/linux/bpf.h            |  1 +
>  include/uapi/linux/inet_diag.h |  1 +
>  include/uapi/linux/sock_diag.h |  8 ++++++
>  include/uapi/linux/unix_diag.h |  1 +
>  net/core/sock_map.c            | 51 ++++++++++++++++++++++++++++++++++
>  net/ipv4/inet_diag.c           |  5 ++++
>  net/unix/diag.c                |  6 ++++
>  7 files changed, 73 insertions(+)
> 

[...]

> +int sock_map_diag_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)) {

wont this be the common case because we call this for any sk from
inet_diag_msg_attrs_fill(sk, ...)? Probably drop the unlikely?

> +		rcu_read_unlock();
> +		return 0;
> +	}