Re: [RFC PATCH bpf-next 6/8] bpf: Add cookie in sk_reuseport_md.

From:   Martin KaFai Lau <redacted>
Date:   Wed, 18 Nov 2020 16:11:54 -0800

On Tue, Nov 17, 2020 at 06:40:21PM +0900, Kuniyuki Iwashima wrote:

quoted

We will call sock_reuseport.prog for socket migration in the next commit,
so the eBPF program has to know which listener is closing in order to
select the new listener.

Currently, we can get a unique ID for each listener in the userspace by
calling bpf_map_lookup_elem() for BPF_MAP_TYPE_REUSEPORT_SOCKARRAY map.
This patch exposes the ID to the eBPF program.

Reviewed-by: Benjamin Herrenschmidt <redacted>
Signed-off-by: Kuniyuki Iwashima <redacted>
---
 include/linux/bpf.h            | 1 +
 include/uapi/linux/bpf.h       | 1 +
 net/core/filter.c              | 8 ++++++++
 tools/include/uapi/linux/bpf.h | 1 +
 4 files changed, 11 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 581b2a2e78eb..c0646eceffa2 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h

@@ -1897,6 +1897,7 @@ struct sk_reuseport_kern {
 	u32 hash;
 	u32 reuseport_id;
 	bool bind_inany;
+	u64 cookie;
 };
 bool bpf_tcp_sock_is_valid_access(int off, int size, enum bpf_access_type type,
 				  struct bpf_insn_access_aux *info);

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 162999b12790..3fcddb032838 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h

@@ -4403,6 +4403,7 @@ struct sk_reuseport_md {
 	__u32 ip_protocol;	/* IP protocol. e.g. IPPROTO_TCP, IPPROTO_UDP */
 	__u32 bind_inany;	/* Is sock bound to an INANY address? */
 	__u32 hash;		/* A hash of the packet 4 tuples */
+	__u64 cookie;		/* ID of the listener in map */

Instead of only adding the cookie of a sk, lets make the sk pointer available:

	__bpf_md_ptr(struct bpf_sock *, sk);

and then use the BPF_FUNC_get_socket_cookie to get the cookie.

Other fields of the sk can also be directly accessed too once
the sk pointer is available.

Oh, I did not know BPF_FUNC_get_socket_cookie.
I will add the sk pointer and use the helper function in the next spin!
Thank you.