[Libguestfs] Note that guestfs now requires json-c (JSON library) instead of Jansson

Libvirt recently moved from yajl (another JSON library) to json-c, because yajl is dead upstream. So that we are using just one JSON library (eg. in Linux distros), I also moved libguestfs, guestfs-tools and virt-v2v over to using json-c. This change takes effect in: - libguestfs >= 1.55.1 (development branch) - guestfs-tools >= 1.53.4 (development branch) - virt-v2v >= 2.7.1 (development branch) (Previous versions like the just released stable libguestfs 1.54.x and virt-v2v 2.6.x branches are NOT changed, and will still require Jansson). That's the easy bit. The _complicated_ bit is what happens if you mix up old libguestfs with new guestfs-tools or virt-v2v (probably the other way round too, but I didn't test that). It depends if you're using Jansson >= 2.14 or older Jansson. If using Jansson >= 2.14, you can freely mix old/new packages. (The reason is to do with symbol versioning introduced in Jansson 2.14). If using Jansson < 2.14 then you'll hit this error caused by a conflicting symbol across the Jansson and json-c libraries: qemu-img info: JSON output did not contain ‘format’ key If you see that error happening it's because you're mixing old and new libguestfs, guestfs-tools, virt-v2v, AND using Jansson < 2.14. The solution is not to mix them, or if you can't do that, update to the latest Jansson and recompile everything. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW