[libvirt PATCH v4 4/6] conf: add support for 'blob' in virtio video device

[Jonathon Jongsma]

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 at redhat.com>
---
 docs/formatdomain.rst             |  7 +++++++
 src/conf/domain_conf.c            |  6 ++++++
 src/conf/domain_conf.h            |  1 +
 src/conf/domain_validate.c        | 13 ++++++++++---
 src/conf/schemas/domaincommon.rng |  5 +++++
 5 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index 212104fe1f..cf8a09adec 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -6346,6 +6346,13 @@ A video device.
    :since:`since 1.3.3` ) extends secondary bar and makes it addressable as
    64bit memory.
 
+   :since:`Since 8.7.0` (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 c39602ec75..57177b1544 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -12894,6 +12894,9 @@ virDomainVideoModelDefParseXML(virDomainVideoDef *def,
     else if (rc == 0)
         def->heads = 1;
 
+    if (virXMLPropTristateSwitch(node, "blob", VIR_XML_PROP_NONE, &def->blob) < 0)
+        return -1;
+
     return 0;
 }
 
@@ -24973,6 +24976,9 @@ 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 7d293f1d8a..8ab14d6a3c 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -1789,6 +1789,7 @@ 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 1c78a3d31c..1908d4459e 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 7f6ea1d888..80eb8d9ee9 100644
--- a/src/conf/schemas/domaincommon.rng
+++ b/src/conf/schemas/domaincommon.rng
@@ -4378,6 +4378,11 @@
                 <ref name="virYesNo"/>
               </attribute>
             </optional>
+            <optional>
+              <attribute name="blob">
+                <ref name="virOnOff"/>
+              </attribute>
+            </optional>
             <optional>
               <element name="acceleration">
                 <optional>
-- 
2.37.1