Merge pull request iovisor#1615 from palmtenor/lua_biosnoop

Port fixes of biosnoop from Python to Lua

tools/biosnoop.lua

@@ -94,11 +94,21 @@ int trace_req_completion(struct pt_regs *ctx, struct request *req)
  req->rq_disk->disk_name);
  }
 
- if (req->cmd_flags & REQ_WRITE) {
- data.rwflag=1;
- } else {
- data.rwflag=0;
- }
+/*
+ * The following deals with a kernel version change (in mainline 4.7, although
+ * it may be backported to earlier kernels) with how block request write flags
+ * are tested. We handle both pre- and post-change versions here. Please avoid
+ * kernel version tests like this as much as possible: they inflate the code,
+ * test, and maintenance burden.
+ */
+#ifdef REQ_WRITE
+ data.rwflag = !!(req->cmd_flags & REQ_WRITE);
+#elif defined(REQ_OP_SHIFT)
+ data.rwflag = !!((req->cmd_flags >> REQ_OP_SHIFT) == REQ_OP_WRITE);
+#else
+ data.rwflag = !!((req->cmd_flags & REQ_OP_MASK) == REQ_OP_WRITE);
+#endif
+
  events.perf_submit(ctx,&data,sizeof(data));
  start.delete(&req);
  infobyreq.delete(&req);