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    conf: add new <target> subelement with chassisNr attribute to <controller> · 8dc88aee
    Laine Stump 提交于
    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.
    8dc88aee
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