adding fwmark for decaped packets

Summary: adding option (disabled by default) to set fwmark on decapped packets.

Reviewed By: avasylev

Differential Revision: D99727012

fbshipit-source-id: c7a1735f69ac954ede865d5088a00ba51b4bf4a9

Author: Pavel Dubovitsky

katran/decap/tc_bpf/tc_decap.bpf.c

@@ -111,6 +111,9 @@ __attribute__((__always_inline__)) static inline int process_packet(
       if (action >= 0) {
         return action;
       }
+#ifdef ENABLE_DECAP_MARK
+      set_decap_skb_mark(skb);
+#endif
     }
   }
   return TC_ACT_UNSPEC;

katran/decap/tc_bpf/tc_decap_kern_helpers.h

@@ -29,6 +29,17 @@
 #include "katran/lib/linux_includes/bpf.h"
 #include "katran/lib/linux_includes/bpf_helpers.h"
 
+#ifndef TC_DECAP_SKB_MARK
+#define TC_DECAP_SKB_MARK 0xDEC
+#endif
+
+#ifdef ENABLE_DECAP_MARK
+__attribute__((__always_inline__)) static inline void set_decap_skb_mark(
+    struct __sk_buff* skb) {
+  skb->mark = TC_DECAP_SKB_MARK;
+}
+#endif
+
 __attribute__((__always_inline__)) static inline bool tc_decap_v6(
     struct __sk_buff* skb,
     void** data,