common/tracer: fix decoding when jaeger tracing is disabled

We aren't currently using jaeger tracing on Windows. The issue is
that Windows hosts (or any other host that doesn't use jaeger)
are experiencing message decoding failures after a recent change [1].

This change updates the tracer encoding so that messages from
non-jaeger hosts may be decoded by services that use jaeger.

[1] https://github.com/ceph/ceph/pull/47457

Signed-off-by: Lucian Petrut <lpetrut@cloudbasesolutions.com>
This commit rebrings 3701ffa6733b001d4278a0b68395c5efe2382f25 which
got reverted due to an implicit dependency with other revert. Please
see https://github.com/ceph/ceph/pull/52114#issuecomment-1950288188.

Conflicts:
	src/common/tracer.h
	  formatting conflict with 7179ac0037320480f089e1a9e291cdc37282d250

diff --git a/src/common/tracer.h b/src/common/tracer.h
index b039d304a79a8e45b66486945cdf315deabb3c51..ee0b744075454b8a6d594535f9781ed79ae45be6 100644 (file)
--- a/src/common/tracer.h
+++ b/src/common/tracer.h
@@ -152,9 +152,20 @@ struct Tracer {
   jspan_ptr add_span(std::string_view span_name, const jspan_context& parent_ctx) { return {}; }
 };
 
-inline void encode(const jspan_context& span, bufferlist& bl, uint64_t f=0) {}
-inline void decode(jspan_context& span_ctx, ceph::buffer::list::const_iterator& bl) {}
+inline void encode(const jspan_context& span_ctx, bufferlist& bl, uint64_t f = 0) {
+  ENCODE_START(1, 1, bl);
+  // jaeger is missing, set "is_valid" to false.
+  bool is_valid = false;
+  encode(is_valid, bl);
+  ENCODE_FINISH(bl);
+}
 
+inline void decode(jspan_context& span_ctx, bufferlist::const_iterator& bl) {
+  DECODE_START(254, bl);
+  // jaeger is missing, consume the buffer but do not decode it.
+  DECODE_FINISH(bl);
 }
 
+} // namespace tracing
+
 #endif // !HAVE_JAEGER