cls_bpf: introduce integrated actions

Often cls_bpf classifier is used with single action drop attached.
Optimize this use case and let cls_bpf return both classid and action.
For backwards compatibility reasons enable this feature under
TCA_BPF_FLAG_ACT_DIRECT flag.

Then more interesting programs like the following are easier to write:
int cls_bpf_prog(struct __sk_buff *skb)
{
  /* classify arp, ip, ipv6 into different traffic classes
   * and drop all other packets
   */
  switch (skb->protocol) {
  case htons(ETH_P_ARP):
    skb->tc_classid = 1;
    break;
  case htons(ETH_P_IP):
    skb->tc_classid = 2;
    break;
  case htons(ETH_P_IPV6):
    skb->tc_classid = 3;
    break;
  default:
    return TC_ACT_SHOT;
  }

  return TC_ACT_OK;
}

Joint work with Daniel Borkmann.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/uapi/linux/pkt_cls.h b/include/uapi/linux/pkt_cls.h
index 4f0d1bc..0a262a8 100644
--- a/include/uapi/linux/pkt_cls.h
+++ b/include/uapi/linux/pkt_cls.h
@@ -373,6 +373,8 @@
 
 /* BPF classifier */
 
+#define TCA_BPF_FLAG_ACT_DIRECT		(1 << 0)
+
 enum {
 	TCA_BPF_UNSPEC,
 	TCA_BPF_ACT,
@@ -382,6 +384,7 @@
 	TCA_BPF_OPS,
 	TCA_BPF_FD,
 	TCA_BPF_NAME,
+	TCA_BPF_FLAGS,
 	__TCA_BPF_MAX,
 };