Re: [libvirt] [PATCHv3 03/13] conf: add new <target> subelement with chassisNr attribute to <controller>

There are some configuration options to some types of pci controllers that are currently automatically derived from other parts of the controller's configuration. For example, in qemu a pci-bridge controller has an option that is called "chassis_nr"; up until now libvirt has always set chassis_nr to the index of the pci-bridge. So this: <controller type='pci' model='pci-bridge' index='2'/> will always result in: -device pci-bridge,chassis_nr=2,... on the qemu commandline. In the future we may decide there is a better way to derive that option, but even in that case we will need for existing domains to retain the same chassis_nr they were using in the past - that is something that is visible to the guest so it is part of the guest ABI and changing it would lead to problems for migrating guests (or just guests with very picky OSes). The <target> subelement has been added as a place to put the new "chassisNr" attribute that will be filled in by libvirt when it auto-generates the chassisNr; it will be saved in the config, then reused any time the domain is started: <controller type='pci' model='pci-bridge' index='2'> <model type='pci-bridge'/> <target chassisNr='2'/> </controller> The one oddity of all this is that if the controller configuration is changed (for example to change the index or the pci address where the controller is plugged in), the items in <target> will *not* be re-generated, which might lead to conflict. I can't really see any way around this, but fortunately if there is a material conflict qemu will let us know and we will pass that on to the user. --- changes from V2: * check chassisNr for 0-255 range * multiple <target>s in a single controller is now an error * 1.3.0 -> 1.2.18 docs/formatdomain.html.in | 24 +++++++++++++ docs/schemas/domaincommon.rng | 10 ++++++ src/conf/domain_conf.c | 45 +++++++++++++++++++++++-- src/conf/domain_conf.h | 10 +++++- tests/qemuxml2argvdata/qemuxml2argv-q35.xml | 1 + tests/qemuxml2xmloutdata/qemuxml2xmlout-q35.xml | 1 + 6 files changed, 88 insertions(+), 3 deletions(-) diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in index 9abceee..fdf7e82 100644 --- a/docs/formatdomain.html.in +++ b/docs/formatdomain.html.in @@ -3055,6 +3055,30 @@ only).</span> </p> <p> + PCI controllers also have an optional + subelement <code>&lt;target&gt;</code> with the attributes + listed below. These are configurable items that 1) are visible + to the guest OS so must be preserved for guest ABI + compatibility, and 2) are usually left to default values or + derived automatically by libvirt. In almost all cases, you + should not manually add a <code>&lt;target&gt;</code> subelement + to a controller, nor should you modify the values in the those + that are automatically generated by + libvirt. <span class="since">Since 1.2.18 (QEMU only).</span>

+ </p> + <dl> + <dt><code>chassisNr</code></dt> + <dd> + PCI controllers that have attribute model="pci-bridge", can + also have a <code>chassisNr</code> attribute in + the <code>&lt;target&gt;</code> subelement, which is used to + control QEMU's "chassis_nr" option for the pci-bridge device + (normally libvirt automatically sets this to the same value as + the index attribute of the pci controller). If set, chassisNr + must be between 0 and 255. + </dd> + </dl> + <p> For machine types which provide an implicit PCI bus, the pci-root controller with index=0 is auto-added and required to use PCI devices. pci-root has no address. diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c index d58e679..fbad7e9 100644 --- a/src/conf/domain_conf.c +++ b/src/conf/domain_conf.c @@ -7826,6 +7830,15 @@ virDomainControllerDefParseXML(xmlNodePtr node, } modelName = virXMLPropString(cur, "name"); processedModel = true; + } else if (xmlStrEqual(cur->name, BAD_CAST "target")) { + if (processedTarget) { + virReportError(VIR_ERR_XML_ERROR, "%s", + _("Multiple <target> elements in " + "controller definition not allowed")); + goto error; + } + chassisNr = virXMLPropString(cur, "chassisNr"); + processedTarget = true;