Re: [libvirt] [PATCHv5] virtio-rng: Add rate limiting options for virtio-RNG
On Thu, Mar 07, 2013 at 02:09:50PM +0100, Peter Krempa wrote:
Qemu's implementation of virtio RNG supports rate limiting of
the
entropy used. This patch exposes the option to tune this functionality.
This patch is based on qemu commit 904d6f588063fb5ad2b61998acdf1e73fb4
The rate limiting is exported in the XML as:
<devices>
...
<rng model='virtio'>
<rate period='1234'>4321</rate>
I find it wierd that we're mixing use of attributes with text
content here. I'd expect one style, or the other
eg
<rate period="1234" bytes="4321"/>
or
<rate>
<period>1234</period>
<bytes>5432</bytes>
</rate>
I prefer the style using attributes myself.
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 2509193..e19b5c0 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -1721,6 +1721,8 @@ enum virDomainRNGBackend {
struct _virDomainRNGDef {
int model;
int backend;
+ unsigned int rate; /* bits per period */
Why are we using bits instead of bytes ? Do we really need to
be able to control this rate with a granularity of bits? It seems
overkill to me
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 201fac1..c0f8dd2 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -4255,6 +4255,15 @@ qemuBuildRNGDeviceArgs(virCommandPtr cmd,
virBufferAsprintf(&buf, "virtio-rng-pci,rng=%s", dev->info.alias);
+ if (dev->rate > 0) {
+ /* qemu uses bytes */
+ virBufferAsprintf(&buf, ",max-bytes=%u", dev->rate / 8);
I expect we need to use VIR_DIV_UP here ? Though we can avoid
it if we just store bytes ourselves.
Daniel
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