bpf: Add bpf_sk_storage support to bpf_tcp_ca

This patch adds bpf_sk_storage_get() and bpf_sk_storage_delete()
helper to the bpf_tcp_ca's struct_ops. That would allow
bpf-tcp-cc to:
1) share sk private data with other bpf progs.
2) use bpf_sk_storage as a private storage for a bpf-tcp-cc
if the existing icsk_ca_priv is not big enough.

Signed-off-by: Martin KaFai Lau <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Acked-by: Yonghong Song <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

net/ipv4/bpf_tcp_ca.c

···
 #include <linux/btf.h>
 #include <linux/filter.h>
 #include <net/tcp.h>
+#include <net/bpf_sk_storage.h>
 
 static u32 optional_ops[] = {
 	offsetof(struct tcp_congestion_ops, init),
···
 static const struct btf_type *tcp_sock_type;
 static u32 tcp_sock_id, sock_id;
 
+static int btf_sk_storage_get_ids[5];
+static struct bpf_func_proto btf_sk_storage_get_proto __read_mostly;
+
+static int btf_sk_storage_delete_ids[5];
+static struct bpf_func_proto btf_sk_storage_delete_proto __read_mostly;
+
+static void convert_sk_func_proto(struct bpf_func_proto *to, int *to_btf_ids,
+				  const struct bpf_func_proto *from)
+{
+	int i;
+
+	*to = *from;
+	to->btf_id = to_btf_ids;
+	for (i = 0; i < ARRAY_SIZE(to->arg_type); i++) {
+		if (to->arg_type[i] == ARG_PTR_TO_SOCKET) {
+			to->arg_type[i] = ARG_PTR_TO_BTF_ID;
+			to->btf_id[i] = tcp_sock_id;
+		}
+	}
+}
+
 static int bpf_tcp_ca_init(struct btf *btf)
 {
 	s32 type_id;
···
 		return -EINVAL;
 	tcp_sock_id = type_id;
 	tcp_sock_type = btf_type_by_id(btf, tcp_sock_id);
+
+	convert_sk_func_proto(&btf_sk_storage_get_proto,
+			      btf_sk_storage_get_ids,
+			      &bpf_sk_storage_get_proto);
+	convert_sk_func_proto(&btf_sk_storage_delete_proto,
+			      btf_sk_storage_delete_ids,
+			      &bpf_sk_storage_delete_proto);
 
 	return 0;
 }
···
 	switch (func_id) {
 	case BPF_FUNC_tcp_send_ack:
 		return &bpf_tcp_send_ack_proto;
+	case BPF_FUNC_sk_storage_get:
+		return &btf_sk_storage_get_proto;
+	case BPF_FUNC_sk_storage_delete:
+		return &btf_sk_storage_delete_proto;
 	default:
 		return bpf_base_func_proto(func_id);
 	}