[libvirt] [PATCHv5 18/19] qemu: Add support for networked disks for block commit

[Eric Blake]

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.

> ---
>  src/qemu/qemu_driver.c | 39 ++++++++++++++++++++++++++++++++++-----
>  1 file changed, 34 insertions(+), 5 deletions(-)
> 

> +
> +    if (flags & VIR_DOMAIN_BLOCK_COMMIT_RELATIVE &&
> +        topSource != disk->src) {

So you are silently ignoring the flag if topSource is the active layer?
 That's okay, but reflect it in the documentation earlier in the series.

> +        if (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_CHANGE_BACKING_FILE)) {
> +            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
> +                           _("this qemu doesn't support relative blockpull"));
> +            goto endjob;
> +        }
> +
> +        if (virStorageFileGetRelativeBackingPath(topSource, baseSource,
> +                                                 &backingPath) < 0)
> +            goto endjob;
> +
> +        if (!backingPath) {
> +            virReportError(VIR_ERR_OPERATION_INVALID, "%s",
> +                           _("Can't keep relative backing relationship."));

No '.' at end of the message.

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.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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