On 05/15/2014 12:22 PM, Jeff Cody wrote: >> Hmm - how will this be discoverable by libvirt? Maybe when libvirt is >> doing the 'qemu -m none' probing, it can hotplug a device pointing to >> /dev/null (libvirt _already_ does that to test if add-fd works), and >> intentionally omit a node name. If libvirt then queries the device, and >> sees that the __qemu##000NNNN node-name was auto-assigned, then it can >> be assumed that this qemu is new enough to provide node-names for ALL >> operations (but that means this series is incomplete unless we add >> node-name support to all remaining block commands, such as block-stream, >> drive-mirror, and drive-backup). This part is where I wonder if patch >> 1/5 should be rebased to be last in the series. >> > > Ah... I had originally planned on submitting separate patches for each > of the block jobs, to make reviewing easier. But your idea on how > libvirt can discover this is a good one, and would mandate changing > those commands all in one series to be effective. So this series will > grow by a few patches. :) > > If libvirt is going to use the autogenerated string format for > decisions, we should also document the string format in the QAPI docs.
Adding a new command is much easier to probe for (a single query-commands, which we are already using) than requiring a sequence of operations (hotplug, then query to see if a name was assigned), and probably even more direct (if the standalone command exists, then so does the integrated use of setting backing names). >> >> In short, this new command option allows the equivalent of 'qemu-img >> rebase -u' on a live image. Definitely a needed functionality. >> > > Would it be useful to have a stand-alone QMP command to change the > backing-file, as well? As this stands, it will only change the > backing file if you are also merging data down the chain. > > If you want/need the ability to do a true 'qemu-img rebase -u' on any > given image without other chain modification, that needs a new > command. Yes, I think that's probably a wise idea to provide a dedicated command for just changing the name recorded in a backing file. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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