[Qemu-devel] [PATCH 2/2 v2] virtio-rng: Serve pending request if any after timer bumps up quota.

[Pankaj Gupta <pagupta@redhat.com>]

We are arming timer when we get first request from guest.
Even if guest pulls all the data we will be serving guest 
only when timer bumps up new quota. When timer expires 
we check if we have a pending request from guest, we 
serve it and rearm the timer else we don't do any thing.

This patch also moves out 'request size' logic out to 
'check_request' function so that can be re-used.

Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
---
 hw/virtio/virtio-rng.c | 36 ++++++++++++++++++++++++------------
 1 file changed, 24 insertions(+), 12 deletions(-)

diff --git a/hw/virtio/virtio-rng.c b/hw/virtio/virtio-rng.c
index 8774a0c..dca5064 100644
--- a/hw/virtio/virtio-rng.c
+++ b/hw/virtio/virtio-rng.c
@@ -37,6 +37,24 @@ static size_t get_request_size(VirtQueue *vq, unsigned quota)
     return in;
 }
 
+static size_t check_request(VirtIORNG *vrng)
+{
+    size_t size;
+    unsigned quota;
+
+    if (vrng->quota_remaining < 0) {
+        quota = 0;
+    } else {
+        quota = MIN((uint64_t)vrng->quota_remaining, (uint64_t)UINT32_MAX);
+    }
+    size = get_request_size(vrng->vq, quota);
+
+    trace_virtio_rng_request(vrng, size, quota);
+
+    size = MIN(vrng->quota_remaining, size);
+    return size;
+}
+
 static void virtio_rng_process(VirtIORNG *vrng);
 
 /* Send data from a char device over to the guest */
@@ -72,7 +90,6 @@ static void chr_read(void *opaque, const void *buf, size_t size)
 static void virtio_rng_process(VirtIORNG *vrng)
 {
     size_t size;
-    unsigned quota;
 
     if (!is_guest_ready(vrng)) {
         return;
@@ -83,17 +100,8 @@ static void virtio_rng_process(VirtIORNG *vrng)
                    qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) + vrng->conf.period_ms);
 	vrng->activate_timer = false;
     }
+    size = check_request(vrng);
 
-    if (vrng->quota_remaining < 0) {
-        quota = 0;
-    } else {
-        quota = MIN((uint64_t)vrng->quota_remaining, (uint64_t)UINT32_MAX);
-    }
-    size = get_request_size(vrng->vq, quota);
-
-    trace_virtio_rng_request(vrng, size, quota);
-
-    size = MIN(vrng->quota_remaining, size);
     if (size) {
         rng_backend_request_entropy(vrng->rng, size, chr_read, vrng);
     }
@@ -142,9 +150,13 @@ static int virtio_rng_load(QEMUFile *f, void *opaque, int version_id)
 static void check_rate_limit(void *opaque)
 {
     VirtIORNG *vrng = opaque;
+    size_t size;
 
     vrng->quota_remaining = vrng->conf.max_bytes;
-    virtio_rng_process(vrng);
+    size = check_request(vrng);
+    if (size > 0) {
+        virtio_rng_process(vrng);
+    }
     vrng->activate_timer = true;
 }
 
-- 
1.9.3