virtio-rng: trigger timer only when guest requests for entropy

This patch triggers timer only when guest requests for
entropy. As soon as first request from guest for entropy
comes we set the timer. Timer bumps up the quota value
when it gets triggered.

Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Message-Id: <1436962608-9961-2-git-send-email-pagupta@redhat.com>

[Re-worded patch subject, removed extra whitespace -- Amit]

Signed-off-by: Amit Shah <amit.shah@redhat.com>

hw/virtio/virtio-rng.c

@@ -77,6 +77,12 @@ static void virtio_rng_process(VirtIORNG *vrng)
         return;
     }
 
+    if (vrng->activate_timer) {
+        timer_mod(vrng->rate_limit_timer,
+                  qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) + vrng->conf.period_ms);
+        vrng->activate_timer = false;
+    }
+
     if (vrng->quota_remaining < 0) {
         quota = 0;
     } else {
@@ -138,8 +144,7 @@ static void check_rate_limit(void *opaque)
 
     vrng->quota_remaining = vrng->conf.max_bytes;
     virtio_rng_process(vrng);
-    timer_mod(vrng->rate_limit_timer,
-                   qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) + vrng->conf.period_ms);
+    vrng->activate_timer = true;
 }
 
 static void virtio_rng_device_realize(DeviceState *dev, Error **errp)
@@ -195,13 +200,9 @@ static void virtio_rng_device_realize(DeviceState *dev, Error **errp)
 
     vrng->vq = virtio_add_queue(vdev, 8, handle_input);
     vrng->quota_remaining = vrng->conf.max_bytes;
-
     vrng->rate_limit_timer = timer_new_ms(QEMU_CLOCK_VIRTUAL,
                                                check_rate_limit, vrng);
-
-    timer_mod(vrng->rate_limit_timer,
-                   qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) + vrng->conf.period_ms);
-
+    vrng->activate_timer = true;
     register_savevm(dev, "virtio-rng", -1, 1, virtio_rng_save,
                     virtio_rng_load, vrng);
 }

include/hw/virtio/virtio-rng.h

@@ -44,6 +44,7 @@ typedef struct VirtIORNG {
      */
     QEMUTimer *rate_limit_timer;
     int64_t quota_remaining;
+    bool activate_timer;
 } VirtIORNG;
 
 #endif