Re: [Libguestfs] [PATCH] v2v: Allow libvirt >= 2.1.0 to be used for Xen and vCenter conversions.

Libvirt >= 2.1.0 now allows you to open files which have a "json:" QEMU pseudo-URL as backingfile, whereas previously it would fail hard in this case (RHBZ#1134878). When virt-v2v performs conversions from Xen (over SSH) or vCenter (over HTTPS) it uses these pseudo-URLs as backingfiles. We had to tell people to use LIBGUESTFS_BACKEND=direct to avoid libvirt in this situation. This commit narrows the check so it will now only print the error if libvirt < 2.1.0 and LIBGUESTFS_BACKEND=direct is not set. Also the error is modified to tell users they can either upgrade libvirt or set LIBGUESTFS_BACKEND=direct to work around the problem. Note there is not an easy way apart from checking the version number of libvirt to tell if the json pseudo-URL is supported. As a side-effect, this commit also prints the libvirt version number in debugging output when virt-v2v starts up, which is sometimes useful information for narrowing down bugs (it is in fact already printed by libguestfs, so this is duplicate information, but it's a bit easier to find when it's at the top of the debug). Thanks: Peter Krempa. ---