On 06/25/2014 12:13 PM, Adam Litke wrote:
On 25/06/14 10:27 -0600, Eric Blake wrote:
On 06/19/2014 07:59 AM, Peter Krempa wrote:
Now that we are able to select images from the backing chain via indexed access we should also convert possible network sources to qemu-compatible strings before passing them to qemu.
Eventually, we'll want to use qemu's node-name functionality, also being added (but possibly in qemu 2.2 instead of 2.1, depends on how Jeff's series goes). But for the simpler case of all files being local or all files being network from the same pool (that is, no mixed-mode chains), then this does appear to work at getting a decent name into qemu, at which point qemu can indeed commit to the right target.
Wait - the earlier patches said that relative names would be preserved if possible, implying that an absolute name would still be used if a relative name was not possible. But this errors out if a relative name was not possible. Which is nicer to the end user, treating the flag as advisory or mandatory? I'm hoping Adam can answer which he'd prefer, as one of the first clients of this new feature.
Thanks Eric. If the flag was specified we need it to fail if a relative backing path is not possible. Otherwise the backing chain could be rewritten such that the VM can not be started on a different host in the future. For us, not honoring the flag is a corruption.
Okay, let's go with mandatory semantics on the respin of this series. If the flag is present, we fail unless we were able to write a relative name into the affected file (which implies that using the flag while the chain already had absolute names is a guaranteed failure).
For those applications that don't mind (or might handle abs paths differently than relative ones, they could retry the operation without the flag. Perhaps we'll want a specific error code for this scenario to make it easy to handle?
I wouldn't bother with a special error code unless someone specifically asks for it in their use case. We can always add it later, if needed. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org