virtio-rng: add rate limiting support

This adds parameters to virtio-rng-pci to allow rate limiting the entropy a
guest receives.  An example command line:

$ qemu -device virtio-rng-pci,max-bytes=1024,period=1000

Would limit entropy collection to 1Kb/s.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
index a3d4777e8d..f90296d672 100644
--- a/hw/virtio-pci.c
+++ b/hw/virtio-pci.c
@@ -1015,6 +1015,13 @@ static void virtio_rng_initfn(Object *obj)
 
 static Property virtio_rng_properties[] = {
     DEFINE_VIRTIO_COMMON_FEATURES(VirtIOPCIProxy, host_features),
+    /* Set a default rate limit of 2^47 bytes per minute or roughly 2TB/s.  If
+       you have an entropy source capable of generating more entropy than this
+       and you can pass it through via virtio-rng, then hats off to you.  Until
+       then, this is unlimited for all practical purposes.
+    */
+    DEFINE_PROP_UINT64("max-bytes", VirtIOPCIProxy, rng.max_bytes, INT64_MAX),
+    DEFINE_PROP_UINT32("period", VirtIOPCIProxy, rng.period_ms, 1 << 16),
     DEFINE_PROP_END_OF_LIST(),
 };