[libvirt] [PATCH 3/4] virtio-rng: Add rate limiting options for virtio-RNG

[Eric Blake]

On 02/25/2013 03:31 PM, Peter Krempa wrote:
> Qemu's implementation of virtio RNG supports rate limiting of the
> entropy used. This patch exposes the option to tune this fucntionality.

s/fucntionality/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>
>     <backend model='random'/>
>   </rng>
>   ...
> ---
> 
> Notes:
>     This series would benefit from the per-driver XML parsing checks to verify
>     that rate > 8bits, otherwise it will be rounded down to 0 bytes. I will
>     follow up with that change as soon as the per-driver callbacks get in.
> 
>     Version 3:
>     - State the time unit in docs
>     Version 2:
>     - Qemu uses bytes/period, adapt the value according to that
> 
>  docs/formatdomain.html.in                              | 10 ++++++++++
>  docs/schemas/domaincommon.rng                          | 18 +++++++++++++++++-
>  src/conf/domain_conf.c                                 | 17 +++++++++++++++++
>  src/conf/domain_conf.h                                 |  2 ++
>  src/qemu/qemu_command.c                                |  9 +++++++++
>  .../qemuxml2argv-virtio-rng-random.args                |  2 +-
>  .../qemuxml2argv-virtio-rng-random.xml                 |  1 +
>  7 files changed, 57 insertions(+), 2 deletions(-)
> 
> diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
> index 2a60f61..220884c 100644
> --- a/docs/formatdomain.html.in
> +++ b/docs/formatdomain.html.in
> @@ -4294,6 +4294,7 @@ qemu-kvm -net nic,model=? /dev/null
>    ...
>    <devices>
>      <rng model='virtio'>
> +      <rate period="2000">1234</rate>
>        <backend model='random'>/dev/random</backend>
>        <!-- OR -->
>        <backend model='egd' type='udp'>
> @@ -4316,6 +4317,15 @@ qemu-kvm -net nic,model=? /dev/null
>            <li>'virtio' — supported by qemu and virtio-rng kernel module</li>
>          </ul>
>        </dd>
> +      <dt><code>rate</code></dt>
> +      <dd>
> +        <p>
> +          The rate element allows to limit the rate that the entropy can be

grammar doesn't quite flow here; see below

> +          read from the source. The value is in bits that the device is allowed
> +          to read in the selected period. The period is represented in miliseconds.

s/miliseconds/milliseconds/

> +          The default period is 1000ms or 1 second.

I'm still not sure we accurately covered things.  Maybe:

The optional <code>rate</code> element allows limiting the rate at which
entropy can be consumed from the source.  An optional
<code>period</code> attribute specifies the duration of a period in
milliseconds; if omitted, the period is taken as 1000 milliseconds (1
second).  The element contents specify how many bits are permitted per
period.  Drivers may enforce a minimum rate, and may round the rate down
to a minimum granularity.

> +++ b/src/conf/domain_conf.h
> @@ -1736,6 +1736,8 @@ enum virDomainRNGBackend {
>  struct _virDomainRNGDef {
>      int model;
>      int backend;
> +    unsigned int rate;
> +    unsigned int period;

Comments here would help:

unsigned int rate; /* bits per period */
unsigned int period; /* milliseconds */

> +++ b/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.args
> @@ -1 +1 @@
> -LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test /usr/bin/qemu -S -M pc -m 214 -smp 1 -nographic -nodefaults -monitor unix:/tmp/test-monitor,server,nowait -no-acpi -boot c -usb -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3 -object rng-random,id=rng0,filename=/test/phile -device virtio-rng-pci,rng=rng0,bus=pci.0,addr=0x4
> +LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test /usr/bin/qemu -S -M pc -m 214 -smp 1 -nographic -nodefaults -monitor unix:/tmp/test-monitor,server,nowait -no-acpi -boot c -usb -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3 -object rng-random,id=rng0,filename=/test/phile -device virtio-rng-pci,rng=rng0,max-bytes=100,period=1234,bus=pci.0,addr=0x4

This is a long line; please split it with a backslash-newline to fit in
80 columns.

> diff --git a/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.xml b/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.xml
> index ab1f38c..26ddd38 100644
> --- a/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.xml
> +++ b/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.xml
> @@ -17,6 +17,7 @@
>      <controller type='usb' index='0'/>
>      <memballoon model='virtio'/>
>      <rng model='virtio'>
> +      <rate period='1234'>800</rate>
>        <backend model='random'>/test/phile</backend>
>      </rng>
>    </devices>
> 

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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