biotop.py: fix compiler error on newer kernels

man/man8/biotop.8

@@ -65,7 +65,7 @@ Cached process name, if present. This usually (but isn't guaranteed) to identify
 the responsible process for the I/O.
 .TP
 D
-Direction: R == read, W == write.
+Direction: R == read, W == write. This is a simplification.
 .TP
 MAJ
 Major device number.

tools/biotop.py

@@ -68,7 +68,7 @@ def signal_ignore(signal, frame):
 // the key for the output summary
 struct info_t {
  u32 pid;
- int type;
+ int rwflag;
  int major;
  int minor;
  char name[TASK_COMM_LEN];
@@ -128,7 +128,19 @@ def signal_ignore(signal, frame):
  struct info_t info = {};
  info.major = req->rq_disk->major;
  info.minor = req->rq_disk->first_minor;
- info.type = req->cmd_flags & REQ_WRITE;
+/*
+ * 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
+ info.rwflag = !!(req->cmd_flags & REQ_WRITE);
+#else
+ info.rwflag = !!((req->cmd_flags >> REQ_OP_SHIFT) == REQ_OP_WRITE);
+#endif
+
  whop = whobyreq.lookup(&req);
  if (whop == 0) {
  // missed pid who, save stats as pid 0
@@ -199,7 +211,7 @@ def signal_ignore(signal, frame):
  # print line
  avg_ms = (float(v.us) / 1000) / v.io
  print("%-6d %-16s %1s %-3d %-3d %-8s %5s %7s %6.2f" % (k.pid, k.name,
- "W" if k.type else "R", k.major, k.minor, diskname, v.io,
+ "W" if k.rwflag else "R", k.major, k.minor, diskname, v.io,
  v.bytes / 1024, avg_ms))
 
  line += 1