Mark McLoughlin wrote: > So, when libvirt creates a guest for the first time, it makes a copy of > the device tree and continues to use that even if qemu is upgraded. > That's enough to ensure compat is retained for all built-in devices. > > However, in order to retain compat for that SCSI device (e.g. ensuring > the PCI address doesn't change as other devices are added an removed), > we're back to the same problem ... either: > > 1) Use '-drive file=foo.img,if=scsi,pci_addr=foo'; in order to figure > out what address to use, libvirt would need to query qemu for what > address was originally allocated to device or it would do all the > PCI address allocation itself ... or: > > 2) Don't use the command line, instead get a dump of the entire > device tree (including the SCSI device) - if the device is to be > removed or modified in future, libvirt would need to modify the > device tree > > The basic problem would be that the command line config would have very > limited ability to override the device tree config. > After libvirt has done -drive file=foo... it should dump the machine config and use that from then on. To combined to a single thread... > How do you add a new attribute to the device tree and, when a supplied > device tree lacking said attribute, distinguish between a device tree > from an old version of qemu (i.e. use the old default) and a partial > device tree from the VM manager (i.e. use the new default) ? > Please define "attribute". I don't follow what you're asking. >> NB the device tree contains no host configuration information. >> > > So, it wouldn't e.g. include the path to the image file for a block > device? That would always be specified on the command line? > No, the IDE definition would contain some sort of symbolic node name. A separate mechanism (either command line or host config file) would then link a image file to the symbolic name. libvirt should really never worry about the machine config file for normal things unless it needs to change what devices are exposed to a guest. Regards, Anthony Liguori _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
