Re: [libvirt] Reporting log/error messages through capabilities

When qemu is completely broken, libvirtd starts up OK but exists in a kind of broken state where no guests can possibly be run. I hit this problem ... again ... today: https://bugzilla.redhat.com/show_bug.cgi?id=1066630#c0 There is a libvirt bug here, which is that it's very hard to diagnose what is going on when qemu fails to work at all. The logging system in libvirt(d) is trememdously powerful, but ultimately confusing to use, and requires users to edit config files which makes it a non-starter for programs using libvirt through the API [1]. >From a libguestfs point of view, it's impossible for us to report back to the user that there is a problem two layers below in qemu. So my idea is that libvirt capabilities output should have an <info> section containing log messages/errors. <capabilities> ... <info> Could not run qemu-system-blah: "symbol lookup error: /usr/bin/qemu-system-s390x: undefined symbol: glfs_discard_async" </info> </capabilities> Libguestfs queries for libvirt capabilities anyway. If we don't get a satisfactory set of <guest/> elements, then we could list out the <info/> section. Easy for us. The problem is the <info/> element hardly fits into capabilities. If we didn't put it there, could it go some other place? Or a new API?