[libvirt PATCH v6 6/8] conf: add support for 'blob' in virtio video device

[Jonathon Jongsma <jjongsma@xxxxxxxxxx>]

Add the ability to enable blob resources for the virtio video device.
This will accelerate the display path due to less or no copying of pixel
data.

Blob resource support can be enabled with e.g.:

    <video>
      <model type='virtio' blob='on'/>
    </video>

Some additional background information about blob resources:
https://lists.freedesktop.org/archives/dri-devel/2020-August/275972.html
https://www.kraxel.org/blog/2021/05/virtio-gpu-qemu-graphics-update/

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2032406

Signed-off-by: Jonathon Jongsma <jjongsma@xxxxxxxxxx>
Reviewed-by: Ján Tomko <jtomko@xxxxxxxxxx>
---
 docs/formatdomain.rst             |  7 +++++++
 src/conf/domain_conf.c            |  5 +++++
 src/conf/domain_conf.h            |  1 +
 src/conf/domain_validate.c        | 13 ++++++++++---
 src/conf/schemas/domaincommon.rng |  5 +++++
 5 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index fbbee99a80..59d83bdf3c 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -6427,6 +6427,13 @@ A video device.
    :since:`since 1.3.3` ) extends secondary bar and makes it addressable as
    64bit memory.
 
+   :since:`Since 8.10.0` (QEMU driver only), devices with type "virtio" have an
+   optional ``blob`` attribute that can be set to "on" or "off". Setting
+   ``blob`` to "on" will enable the use of blob resources in the device. This
+   can accelerate the display path by reducing or eliminating copying of pixel
+   data between the guest and host. Note that blob resource support requires
+   QEMU version 6.1 or newer.
+
    :since:`Since 5.9.0` , the ``model`` element may also have an optional
    ``resolution`` sub-element. The ``resolution`` element has attributes ``x``
    and ``y`` to set the minimum resolution for the video device. This
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index fcc65011b0..a7ee12defe 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -12865,6 +12865,9 @@ virDomainVideoModelDefParseXML(virDomainVideoDef *def,
     if (virXMLPropUIntDefault(node, "heads", 10, VIR_XML_PROP_NONE, &def->heads, 1) < 0)
         return -1;
 
+    if (virXMLPropTristateSwitch(node, "blob", VIR_XML_PROP_NONE, &def->blob) < 0)
+        return -1;
+
     return 0;
 }
 
@@ -25177,6 +25180,8 @@ virDomainVideoDefFormat(virBuffer *buf,
         virBufferAsprintf(buf, " heads='%u'", def->heads);
     if (def->primary)
         virBufferAddLit(buf, " primary='yes'");
+    if (def->blob != VIR_TRISTATE_SWITCH_ABSENT)
+        virBufferAsprintf(buf, " blob='%s'", virTristateSwitchTypeToString(def->blob));
     if (def->accel || def->res) {
         virBufferAddLit(buf, ">\n");
         virBufferAdjustIndent(buf, 2);
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 8890f5a3a5..5bd5c0d5e4 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -1837,6 +1837,7 @@ struct _virDomainVideoDef {
     bool primary;
     virDomainVideoAccelDef *accel;
     virDomainVideoResolutionDef *res;
+    virTristateSwitch blob;
     virDomainVideoDriverDef *driver;
     virDomainDeviceInfo info;
     virDomainVirtioOptions *virtio;
diff --git a/src/conf/domain_validate.c b/src/conf/domain_validate.c
index 5559a71e14..10eeceda74 100644
--- a/src/conf/domain_validate.c
+++ b/src/conf/domain_validate.c
@@ -225,9 +225,16 @@ virDomainVideoDefValidate(const virDomainVideoDef *video,
         }
     }
 
-    if (video->type != VIR_DOMAIN_VIDEO_TYPE_VIRTIO &&
-        (virDomainCheckVirtioOptionsAreAbsent(video->virtio) < 0))
-        return -1;
+    if (video->type != VIR_DOMAIN_VIDEO_TYPE_VIRTIO) {
+        if (virDomainCheckVirtioOptionsAreAbsent(video->virtio) < 0)
+            return -1;
+        if (video->blob != VIR_TRISTATE_SWITCH_ABSENT) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                           _("video type '%s' does not support blob resources"),
+                           virDomainVideoTypeToString(video->type));
+            return -1;
+        }
+    }
 
     return 0;
 }
diff --git a/src/conf/schemas/domaincommon.rng b/src/conf/schemas/domaincommon.rng
index 14044811c0..5661b930f7 100644
--- a/src/conf/schemas/domaincommon.rng
+++ b/src/conf/schemas/domaincommon.rng
@@ -4481,6 +4481,11 @@
                 <ref name="virYesNo"/>
               </attribute>
             </optional>
+            <optional>
+              <attribute name="blob">
+                <ref name="virOnOff"/>
+              </attribute>
+            </optional>
             <optional>
               <element name="acceleration">
                 <optional>
-- 
2.39.0