conf: Support for Block Device IO Limits

Introducing a new iolimits element allowing to override certain
properties of a guest block device like the physical and logical
block size.
This can be useful for platforms with 'non-standard' disk formats
like S390 DASD with its 4K block size.

Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>

2 files changed, 35 insertions, 0 deletions

diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index 671ce170e..d8ad54ac8 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -1264,6 +1264,7 @@
       <driver name='qemu' type='raw'/>
       <source dev='/dev/sda'/>
       <geometry cyls='16383' heads='16' secs='63' trans='lba'/>
+      <iolimits logical_block_size='512' physical_block_size='4096'/>
       <target dev='hda' bus='ide'/>
     </disk>
   </devices>
@@ -1632,6 +1633,23 @@
             BIOS-Translation-Modus (none, lba or auto)</dd>
         </dl>
       </dd>
+      <dt><code>iolimits</code></dt>
+      <dd>If present, the <code>iolimits</code> element allows
+        to override any of the block device properties listed below.
+        <span class="since">Since 0.10.2 (QEMU and KVM)</span>
+        <dl>
+          <dt><code>logical_block_size</code></dt>
+          <dd>The logical block size the disk will report to the guest
+            OS. For Linux this would be the value returned by the
+            BLKSSZGET ioctl and describes the smallest units for disk
+            I/O.
+          <dt><code>physical_block_size</code></dt>
+          <dd>The physical block size the disk will report to the guest
+            OS. For Linux this would be the value returned by the
+            BLKPBSZGET ioctl and describes the disk's hardware sector
+            size which can be relevant for the alignment of disk data.
+        </dl>
+      </dd>
     </dl>
 
     <h4><a name="elementsFilesystems">Filesystems</a></h4>
diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index 145caf78d..60cf33e0f 100644
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@@ -886,6 +886,9 @@
       <optional>
         <ref name="geometry"/>
       </optional>
+      <optional>
+        <ref name="diskIoLimits"/>
+      </optional>
     </interleave>
   </define>
   <define name="snapshot">
@@ -1110,6 +1113,20 @@
       </optional>
     </element>
   </define>
+  <define name="diskIoLimits">
+    <element name="iolimits">
+      <optional>
+        <attribute name="logical_block_size">
+          <data type="integer"/>
+        </attribute>
+      </optional>
+      <optional>
+        <attribute name="physical_block_size">
+          <data type="integer"/>
+        </attribute>
+      </optional>
+    </element>
+  </define>
   <!--
       Disk may use a special driver for access.
     -->