bpf/flow_dissector: pass input flags to BPF flow dissector program

C flow dissector supports input flags that tell it to customize parsing
by either stopping early or trying to parse as deep as possible. Pass
those flags to the BPF flow dissector so it can make the same
decisions. In the next commits I'll add support for those flags to
our reference bpf_flow.c

v3:
* Export copy of flow dissector flags instead of moving (Alexei Starovoitov)
Acked-by: Petar Penkov <ppenkov@google.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Acked-by: Song Liu <songliubraving@fb.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Petar Penkov <ppenkov@google.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/skbuff.h

@@ -1271,7 +1271,7 @@ static inline int skb_flow_dissector_bpf_prog_detach(const union bpf_attr *attr)
 
 struct bpf_flow_dissector;
 bool bpf_flow_dissect(struct bpf_prog *prog, struct bpf_flow_dissector *ctx,
-		      __be16 proto, int nhoff, int hlen);
+		      __be16 proto, int nhoff, int hlen, unsigned int flags);
 
 bool __skb_flow_dissect(const struct net *net,
 			const struct sk_buff *skb,

include/uapi/linux/bpf.h

@@ -3507,6 +3507,10 @@ enum bpf_task_fd_type {
 	BPF_FD_TYPE_URETPROBE,		/* filename + offset */
 };
 
+#define BPF_FLOW_DISSECTOR_F_PARSE_1ST_FRAG		(1U << 0)
+#define BPF_FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL		(1U << 1)
+#define BPF_FLOW_DISSECTOR_F_STOP_AT_ENCAP		(1U << 2)
+
 struct bpf_flow_keys {
 	__u16	nhoff;
 	__u16	thoff;
@@ -3528,6 +3532,7 @@ struct bpf_flow_keys {
 			__u32	ipv6_dst[4];	/* in6_addr; network order */
 		};
 	};
+	__u32	flags;
 };
 
 struct bpf_func_info {

net/bpf/test_run.c

@@ -419,7 +419,7 @@ int bpf_prog_test_run_flow_dissector(struct bpf_prog *prog,
 	time_start = ktime_get_ns();
 	for (i = 0; i < repeat; i++) {
 		retval = bpf_flow_dissect(prog, &ctx, eth->h_proto, ETH_HLEN,
-					  size);
+					  size, 0);
 
 		if (signal_pending(current)) {
 			preempt_enable();

net/core/flow_dissector.c

@@ -784,7 +784,7 @@ static void __skb_flow_bpf_to_target(const struct bpf_flow_keys *flow_keys,
 }
 
 bool bpf_flow_dissect(struct bpf_prog *prog, struct bpf_flow_dissector *ctx,
-		      __be16 proto, int nhoff, int hlen)
+		      __be16 proto, int nhoff, int hlen, unsigned int flags)
 {
 	struct bpf_flow_keys *flow_keys = ctx->flow_keys;
 	u32 result;
@@ -795,6 +795,14 @@ bool bpf_flow_dissect(struct bpf_prog *prog, struct bpf_flow_dissector *ctx,
 	flow_keys->nhoff = nhoff;
 	flow_keys->thoff = flow_keys->nhoff;
 
+	BUILD_BUG_ON((int)BPF_FLOW_DISSECTOR_F_PARSE_1ST_FRAG !=
+		     (int)FLOW_DISSECTOR_F_PARSE_1ST_FRAG);
+	BUILD_BUG_ON((int)BPF_FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL !=
+		     (int)FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL);
+	BUILD_BUG_ON((int)BPF_FLOW_DISSECTOR_F_STOP_AT_ENCAP !=
+		     (int)FLOW_DISSECTOR_F_STOP_AT_ENCAP);
+	flow_keys->flags = flags;
+
 	preempt_disable();
 	result = BPF_PROG_RUN(prog, ctx);
 	preempt_enable();
@@ -914,7 +922,7 @@ bool __skb_flow_dissect(const struct net *net,
 			}
 
 			ret = bpf_flow_dissect(attached, &ctx, n_proto, nhoff,
-					       hlen);
+					       hlen, flags);
 			__skb_flow_bpf_to_target(&flow_keys, flow_dissector,
 						 target_container);
 			rcu_read_unlock();