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[libvirt] [PATCHv4] virtio-rng: Add rate limiting options for virtio-RNG



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>
    <backend model='random'/>
  </rng>
  ...
---

Notes:
    Version 4:
    - Reword docs
    - state it is available since 1.0.4 as the tree is frozen and this was actually never acked before
    Version 3:
    - State the time unit in docs
    Version 2:
    - Qemu uses bytes/period, adapt the value according to that

 docs/formatdomain.html.in                              | 13 +++++++++++++
 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, 60 insertions(+), 2 deletions(-)

diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index 1835b39..1c6c73e 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -4280,6 +4280,7 @@ qemu-kvm -net nic,model=? /dev/null
   ...
   &lt;devices&gt;
     &lt;rng model='virtio'&gt;
+      &lt;rate period="2000"&gt;1234&lt;/rate&gt;
       &lt;backend model='random'&gt;/dev/random&lt;/backend&gt;
       &lt;!-- OR --&gt;
       &lt;backend model='egd' type='udp'&gt;
@@ -4302,6 +4303,18 @@ qemu-kvm -net nic,model=? /dev/null
           <li>'virtio' &mdash; supported by qemu and virtio-rng kernel module</li>
         </ul>
       </dd>
+      <dt><code>rate</code></dt>
+      <dd>
+        <p>
+          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.
+        </p>
+      </dd>
       <dt><code>backend</code></dt>
       <dd>
         <p>
diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index e7231cc..172926c 100644
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@@ -3500,7 +3500,12 @@
           <value>virtio</value>
         </choice>
       </attribute>
-      <ref name="rng-backend"/>
+      <interleave>
+        <ref name="rng-backend"/>
+        <optional>
+          <ref name="rng-rate"/>
+        </optional>
+      </interleave>
     </element>
   </define>

@@ -3524,6 +3529,17 @@
     </element>
   </define>

+  <define name="rng-rate">
+    <element name="rate">
+      <optional>
+        <attribute name="period">
+          <ref name="positiveInteger"/>
+        </attribute>
+      </optional>
+      <ref name="positiveInteger"/>
+    </element>
+  </define>
+
   <define name="usbmaster">
     <element name="master">
       <attribute name="startport">
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 995cf0c..f556e4c 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -7399,6 +7399,17 @@ virDomainRNGDefParseXML(const xmlNodePtr node,

     ctxt->node = node;

+    if (virXPathUInt("string(./rate)", ctxt, &def->rate) < -1) {
+        virReportError(VIR_ERR_XML_ERROR, "%s", _("invalid RNG rate value"));
+        goto error;
+    }
+
+    if (def->rate > 0 &&
+        virXPathUInt("string(./rate/@period)", ctxt, &def->period) < -1) {
+        virReportError(VIR_ERR_XML_ERROR, "%s", _("invalid RNG period value"));
+        goto error;
+    }
+
     if ((nbackends = virXPathNodeSet("./backend", ctxt, &backends)) < 0)
         goto error;

@@ -13708,6 +13719,12 @@ virDomainRNGDefFormat(virBufferPtr buf,
     const char *backend = virDomainRNGBackendTypeToString(def->backend);

     virBufferAsprintf(buf, "    <rng model='%s'>\n", model);
+    if (def->rate) {
+        virBufferAddLit(buf, "      <rate");
+        if (def->period)
+            virBufferAsprintf(buf, " period='%u'", def->period);
+        virBufferAsprintf(buf, ">%u</rate>\n", def->rate);
+    }
     virBufferAsprintf(buf, "      <backend model='%s'", backend);

     switch ((enum virDomainRNGBackend) def->backend) {
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 5828ae2..1546f21 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 */
+    unsigned int period; /* milliseconds */

     union {
         char *file; /* file name for 'random' source */
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 1c9bfc9..6fcc093 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);
+        if (dev->period)
+            virBufferAsprintf(&buf, ",period=%u", dev->period);
+        else
+            virBufferAddLit(&buf, ",period=1000");
+    }
+
     if (qemuBuildDeviceAddressStr(&buf, &dev->info, qemuCaps) < 0)
         goto cleanup;

diff --git a/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.args b/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.args
index ad27132..4a0437b 100644
--- a/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.args
+++ b/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.args
@@ -3,4 +3,4 @@ LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test /usr/bin/qemu \
 -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/ph<ile' \
--device virtio-rng-pci,rng=rng0,bus=pci.0,addr=0x4
+-device virtio-rng-pci,rng=rng0,max-bytes=100,period=1234,bus=pci.0,addr=0x4
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.xml b/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.xml
index 0658f4b..3899408 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/ph&lt;ile</backend>
     </rng>
   </devices>
-- 
1.8.1.1


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