[libvirt PATCH v3 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             |  6 ++++++
 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, 28 insertions(+), 3 deletions(-)

diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index 993c65e50b..2161cc7e30 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -6198,6 +6198,12 @@ A video device.
    :since:`since 1.3.3` ) extends secondary bar and makes it addressable as
    64bit memory.
 
+   :since:`Since 8.2.0`, 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.
+
    :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 60c27ddd34..ae86f455bd 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -14154,6 +14154,9 @@ 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;
 }
 
@@ -26075,6 +26078,9 @@ 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 acd0588e9b..afa6db2403 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -1763,6 +1763,7 @@ 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 18eb8d697d..da0ff06570 100644
--- a/src/conf/domain_validate.c
+++ b/src/conf/domain_validate.c
@@ -226,9 +226,16 @@ 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 2544864eb4..16b3fd9c53 100644
--- a/src/conf/schemas/domaincommon.rng
+++ b/src/conf/schemas/domaincommon.rng
@@ -4251,6 +4251,11 @@
                 <ref name="virYesNo"/>
               </attribute>
             </optional>
+            <optional>
+              <attribute name="blob">
+                <ref name="virOnOff"/>
+              </attribute>
+            </optional>
             <optional>
               <element name="acceleration">
                 <optional>
-- 
2.35.1