Pass rootId in SDT for shallow copied RCs

Summary:
The shallow copied child RC is often used to make small changes to the RC for a limited scope of the request.

The tracepoint however reports the raw address of the RC as a way to identify the request itself - Therefore we end up reporting different identifiers for what is 'logically' the same request.

This diff adds two additional arguments (the rootIds or pointers to the parent RC) to allow bpf programs to pick up this subtlety.

Reviewed By: yfeldblum

Differential Revision: D22424318

fbshipit-source-id: f669cabca10fa50b8a81fb4b3585d30654207e4c

folly/io/async/Request.cpp

@@ -738,7 +738,9 @@ void exec_set_difference(const TData& data, const TData& other, TExec&& exec) {
       folly,
       request_context_switch_before,
       staticCtx.first.get(),
-      newCtx.get());
+      newCtx.get(),
+      staticCtx.first ? staticCtx.first->getRootId() : 0,
+      newCtx ? newCtx->getRootId() : 0);
 
   if ((newCtx.get() && newCtx->useHazptr()) ||
       (staticCtx.first.get() && staticCtx.first->useHazptr())) {