[Libguestfs] Supporting btrfs subvolumes during inspection

We've currently got a bug in libguestfs which means we can't inspect filesystems in btrfs subvolumes: https://bugzilla.redhat.com/show_bug.cgi?id=824021 This is the default configuration if you select btrfs in F17+. The issue is that it requires an api to fix it, as the return values of inspect_os, inspect_get_filesystems and inspect_get_mountpoints can't express a btrfs subvolume as they're expected to be the names of block devices. As a starter for 10, I propose the addition of parallel apis suffixed _ext which return annotated device descriptions, e.g.: block:/dev/vda2 btrfsvol:/dev/vda4,root The string before the colon is a descriptor. The format of the string after the colon is custom to the descriptor, and is described in the API. A client program can ignore strings with unknown descriptors. New descriptors can be added as required. The old apis would return the same as the _ext versions, except they would only return block devices. Other devices would be omitted. Matt -- Matthew Booth, RHCA, RHCSS Red Hat Engineering, Virtualisation Team GPG ID: D33C3490 GPG FPR: 3733 612D 2D05 5458 8A8A 1600 3441 EA19 D33C 3490