conf: Add a new xenbus controller option for event channels

Event channels are like PV interrupts and in conjuction with grant frames
form a data transfer mechanism for PV drivers. They are also used for
inter-processor interrupts. Guests with a large number of vcpus and/or
many PV devices many need to increase the maximum default value of 1023.
For this reason the native Xen config format supports the
'max_event_channels' setting. See xl.cfg(5) man page for more details.

Similar to the existing maxGrantFrames option, add a new xenbus controller
option 'maxEventChannels', allowing to adjust the maximum value via libvirt.

Signed-off-by: Jim Fehlig <jfehlig@suse.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

docs/formatdomain.html.in

@@ -4464,7 +4464,7 @@
     <driver iothread='4'/>
     <address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/>
   </controller>
-  <controller type='xenbus' maxGrantFrames='64'/>
+  <controller type='xenbus' maxGrantFrames='64' maxEventChannels='2047'/>
   ...
 </devices>
 ...</pre>
@@ -4524,7 +4524,11 @@
         <dd><span class="since">Since 5.2.0</span>, the <code>xenbus</code>
         controller has an optional attribute <code>maxGrantFrames</code>,
         which specifies the maximum number of grant frames the controller
-        makes available for connected devices.</dd>
+        makes available for connected devices.
+        <span class="since">Since 6.3.0</span>, the xenbus controller
+        supports the optional <code>maxEventChannels</code> attribute,
+        which specifies maximum number of event channels (PV interrupts)
+        that can be used by the guest.</dd>
       </dl>
 
     <p>

docs/schemas/domaincommon.rng

@@ -2548,6 +2548,11 @@
                 <ref name="unsignedInt"/>
               </attribute>
             </optional>
+            <optional>
+              <attribute name="maxEventChannels">
+                <ref name="unsignedInt"/>
+              </attribute>
+            </optional>
           </group>
         </choice>
         <optional>

src/conf/domain_conf.c

@@ -2262,6 +2262,7 @@ virDomainControllerDefNew(virDomainControllerType type)
         break;
     case VIR_DOMAIN_CONTROLLER_TYPE_XENBUS:
         def->opts.xenbusopts.maxGrantFrames = -1;
+        def->opts.xenbusopts.maxEventChannels = -1;
         break;
     case VIR_DOMAIN_CONTROLLER_TYPE_IDE:
     case VIR_DOMAIN_CONTROLLER_TYPE_FDC:
@@ -11364,6 +11365,7 @@ virDomainControllerDefParseXML(virDomainXMLOptionPtr xmlopt,
         break;
     case VIR_DOMAIN_CONTROLLER_TYPE_XENBUS: {
         g_autofree char *gntframes = virXMLPropString(node, "maxGrantFrames");
+        g_autofree char *eventchannels = virXMLPropString(node, "maxEventChannels");
 
         if (gntframes) {
             int r = virStrToLong_i(gntframes, NULL, 10,
@@ -11374,6 +11376,15 @@ virDomainControllerDefParseXML(virDomainXMLOptionPtr xmlopt,
                 goto error;
             }
         }
+        if (eventchannels) {
+            int r = virStrToLong_i(eventchannels, NULL, 10,
+                                   &def->opts.xenbusopts.maxEventChannels);
+            if (r != 0 || def->opts.xenbusopts.maxEventChannels < 0) {
+                virReportError(VIR_ERR_INTERNAL_ERROR,
+                               _("Invalid maxEventChannels: %s"), eventchannels);
+                goto error;
+            }
+        }
         break;
     }
 
@@ -25314,6 +25325,10 @@ virDomainControllerDefFormat(virBufferPtr buf,
             virBufferAsprintf(&attrBuf, " maxGrantFrames='%d'",
                               def->opts.xenbusopts.maxGrantFrames);
         }
+        if (def->opts.xenbusopts.maxEventChannels != -1) {
+            virBufferAsprintf(&attrBuf, " maxEventChannels='%d'",
+                              def->opts.xenbusopts.maxEventChannels);
+        }
         break;
 
     default:

src/conf/domain_conf.h

@@ -730,6 +730,7 @@ struct _virDomainUSBControllerOpts {
 
 struct _virDomainXenbusControllerOpts {
     int maxGrantFrames;   /* -1 == undef */
+    int maxEventChannels; /* -1 == undef */
 };
 
 /* Stores the virtual disk controller configuration */