Define new enum types for privHelperServer to handle requests to star…

…t/stop FAM

Summary:
## This Diff

Defined two new enum types to start/stop FAM. These types will be used by privHelperClient to serialize into the requests and by the privHelperServer to decide how to process the requests.

## Context
File Access Monitor(FAM) is a tool to monitor file system access, aiming to find out EdenFS crawlers. The tool will be implemented after the toolchain is ready. Before that, we are going to use [this third-party binary](https://github.com/objective-see/FileMonitor).
This diff stack focuses on integrating the binary into Eden package and spawn a process from privHelper because of the required privileged permission.

Reviewed By: ViniGupta08

Differential Revision: D69340299

fbshipit-source-id: 4cc8176162e7099e4263b9619de3d2a44a60a219

eden/fs/privhelper/PrivHelperConn.h

@@ -51,6 +51,8 @@ class PrivHelperConn {
     REQ_MOUNT_NFS = 11,
     REQ_UNMOUNT_NFS = 12,
     REQ_GET_PID = 13,
+    REQ_START_FAM = 14,
+    REQ_STOP_FAM = 15,
   };
 
   // This structure should never change. If fields need to be added to the
@@ -280,6 +282,12 @@ struct formatter<facebook::eden::PrivHelperConn::MsgType>
       case facebook::eden::PrivHelperConn::REQ_GET_PID:
         name = "REQ_GET_PID";
         break;
+      case facebook::eden::PrivHelperConn::REQ_START_FAM:
+        name = "REQ_START_FAM";
+        break;
+      case facebook::eden::PrivHelperConn::REQ_STOP_FAM:
+        name = "REQ_STOP_FAM";
+        break;
       default:
         name = "Unknown PrivHelperConn::MsgType";
     }

eden/fs/privhelper/PrivHelperServer.cpp

@@ -1373,6 +1373,8 @@ UnixSocket::Message PrivHelperServer::processMessage(
       return processSetUseEdenFs(cursor, request);
     case PrivHelperConn::REQ_GET_PID:
       return processGetPid();
+    case PrivHelperConn::REQ_START_FAM:
+    case PrivHelperConn::REQ_STOP_FAM:
     case PrivHelperConn::MSG_TYPE_NONE:
     case PrivHelperConn::RESP_ERROR:
       break;