Re: [PATCH v1 bpf-next 09/11] bpf: Support bpf_get_socket_cookie_sock() for BPF_PROG_TYPE_SK_REUSEPORT.

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 makes the sk pointer available in sk_reuseport_md so that we can
get the ID by BPF_FUNC_get_socket_cookie() in the eBPF program.

Link: https://lore.kernel.org/netdev/20201119001154.kapwihc2plp4f7zc@kafai-mbp.dhcp.thefacebook.com/ (local)
Suggested-by: Martin KaFai Lau <redacted>
Signed-off-by: Kuniyuki Iwashima <redacted>
---
 include/uapi/linux/bpf.h       |  8 ++++++++
 net/core/filter.c              | 12 +++++++++++-
 tools/include/uapi/linux/bpf.h |  8 ++++++++
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index efe342bf3dbc..3e9b8bd42b4e 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h

@@ -1650,6 +1650,13 @@ union bpf_attr {
  * 		A 8-byte long non-decreasing number on success, or 0 if the
  * 		socket field is missing inside *skb*.
  *
+ * u64 bpf_get_socket_cookie(struct bpf_sock *sk)
+ * 	Description
+ * 		Equivalent to bpf_get_socket_cookie() helper that accepts
+ * 		*skb*, but gets socket from **struct bpf_sock** context.
+ * 	Return
+ * 		A 8-byte long non-decreasing number.
+ *
  * u64 bpf_get_socket_cookie(struct bpf_sock_addr *ctx)
  * 	Description
  * 		Equivalent to bpf_get_socket_cookie() helper that accepts

@@ -4420,6 +4427,7 @@ struct sk_reuseport_md {
 	__u32 bind_inany;	/* Is sock bound to an INANY address? */
 	__u32 hash;		/* A hash of the packet 4 tuples */
 	__u8 migration;		/* Migration type */
+	__bpf_md_ptr(struct bpf_sock *, sk); /* current listening socket */
 };
 
 #define BPF_TAG_SIZE	8

diff --git a/net/core/filter.c b/net/core/filter.c
index 0a0634787bb4..1059d31847ef 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c

@@ -4628,7 +4628,7 @@ static const struct bpf_func_proto bpf_get_socket_cookie_sock_proto = {
 	.func		= bpf_get_socket_cookie_sock,
 	.gpl_only	= false,
 	.ret_type	= RET_INTEGER,
-	.arg1_type	= ARG_PTR_TO_CTX,
+	.arg1_type	= ARG_PTR_TO_SOCKET,