common/ceph_time: make operator<< for timespan less useless

- not a floating point value, which will revert to scientific notation once
  it gets big.
- behave for negative spans

Signed-off-by: Sage Weil <sage@redhat.com>

src/common/ceph_time.cc

@@ -100,7 +100,20 @@ namespace ceph {
   }
 
   std::ostream& operator<<(std::ostream& m, const timespan& t) {
-    return m << std::chrono::duration<double>(t).count() << "s";
+    int64_t ns = t.count();
+    if (ns < 0) {
+      ns = -ns;
+      m << "-";
+    }
+    m << (ns / 1000000000ll);
+    ns %= 1000000000ll;
+    if (ns) {
+      char oldfill = m.fill();
+      m.fill('0');
+      m << '.' << std::setw(9) << ns;
+      m.fill(oldfill);
+    }
+    return m << "s";
   }
 
   template<typename Clock,