qemu-img info currently give me info like this: image: /home/alex/.local/share/gnome-boxes/images/Fedora 16 file format: qcow2 virtual size: 11G (11794287616 bytes) disk size: 4.5G cluster_size: 65536 In order to figure out the "health" of an image there is some more information I would like: in-use disk size - I.e the subset of disk size that is not marked as unused due to e.g. TRIM operations amount of compressed clusters. I.e. "is it useful to re-compress the image". Fragmentation estimation. This would be useful to both sysadmins in general and for automated things like what we want to do in gnome-boxes: https://bugzilla.gnome.org/show_bug.cgi?id=685032
All sounds useful. However these requests should probably go upstream, along with patches! Note upstream there is a patch floating around which adds JSON output to qemu-img info. This is useful because it's a big security problem to try to parse the text output from this command. See: https://lists.gnu.org/archive/html/qemu-devel/2012-09/msg00137.html
Depending on how Boxes wants to consume this extra metadata, this may need to be done in libvirt instead, or as well. Libvirt does not actually use qemu-img info for getting file metadata, since it wants a low overhead code to extra basic properties & forking qemu-img doesn't really satisfy that.
Fragmentation estimation and in-use space is actually quite expensive to compute---not *that* expensive but certainly worse than a fork, and worse-case O(n) in the size of the disk.
Fragmentation statistics have been added to 'qemu-img check' for qcow2 and qed image files: commit f8111c241afa75544032dcfa23df0699c91f9866 Author: Dong Xu Wang <wdongxu.ibm.com> Date: Thu Mar 15 20:13:31 2012 +0800 qemu-img: add image fragmentation statistics Note this is qemu-img check and not qemu-img info, because we need to scan the image metadata (expensive on large images).
Yes, I agree that most of this should be part of 'qemu-img check' rather than 'qemu-img info'. Fragmentation statistics are only implemented for QED as of today, qcow2 doesn't have them yet.
In general I don't think RFE's make much sense in Fedora bugzilla, so I've moved this to the upstream qemu tracker: https://bugs.launchpad.net/qemu/+bug/1090615 Alex, I couldn't find a launchpad account for you, but please follow up on that report (or qemu-devel)