[Qemu-devel] [PATCH] virtio-rng: correct the default limit rate

[Amos Kong]

We have the following comment about the default limit rate:

/* 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.
 */

But the current rate is (INT64_MAX) bytes per (1 << 16) ms, it's 128,000 TB/s

2TB/s is a reasonable rate, so this patch fixes the code, not update the 
document.

* change the default period to 60,000 ms --> 1 mins
* change the default max-bytes to 2^47 bytes --> INT64_MAX >> 16

 INT64_MAX  =  0x 8000 0000 0000 0000 - 1 = 2 ^ 63 - 1
 INT64_MAX >> 16 =  0x 8000 0000 0000 - 1 = 2 ^ 47

Signed-off-by: Amos Kong <address@hidden>
---
 include/hw/virtio/virtio-rng.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/hw/virtio/virtio-rng.h b/include/hw/virtio/virtio-rng.h
index debaa15..d64e804 100644
--- a/include/hw/virtio/virtio-rng.h
+++ b/include/hw/virtio/virtio-rng.h
@@ -53,7 +53,7 @@ typedef struct VirtIORNG {
 */
 #define DEFINE_VIRTIO_RNG_PROPERTIES(_state, _conf_field)                    \
         DEFINE_PROP_UINT64("max-bytes", _state, _conf_field.max_bytes,       \
-                           INT64_MAX),                                       \
-        DEFINE_PROP_UINT32("period", _state, _conf_field.period_ms, 1 << 16)
+                           INT64_MAX >> 16),                                 \
+        DEFINE_PROP_UINT32("period", _state, _conf_field.period_ms, 60000)
 
 #endif
-- 
1.8.3.1