[libvirt PATCH v2 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 ++++++
 docs/schemas/domaincommon.rng |  5 +++++
 src/conf/domain_conf.c        |  6 ++++++
 src/conf/domain_conf.h        |  1 +
 src/conf/domain_validate.c    | 13 ++++++++++---
 5 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index 9202cd3107..62edcea7a7 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -6239,6 +6239,12 @@ A video device.
    :since:`since 1.3.3` ) extends secondary bar and makes it addressable as
    64bit memory.
 
+   :since:`Since 8.1.0`, 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/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index 964b0c9e2f..372376820a 100644
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@@ -4191,6 +4191,11 @@
                 <ref name="virYesNo"/>
               </attribute>
             </optional>
+            <optional>
+              <attribute name="blob">
+                <ref name="virOnOff"/>
+              </attribute>
+            </optional>
             <optional>
               <element name="acceleration">
                 <optional>
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 39aa6a1058..6ea5e62655 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -14114,6 +14114,9 @@ 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;
 }
 
@@ -26000,6 +26003,9 @@ 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 fa64491978..e66f8381e5 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -1736,6 +1736,7 @@ 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 f0b8aa2655..c5c6f7df15 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;
 }
-- 
2.35.1