libguestfs is a set of tools for accessing and modifying virtual machine (VM) disk images. You can use this for viewing and editing files inside guests, scripting changes to VMs, monitoring disk used/free statistics, P2V, V2V, performing partial backups, cloning VMs, and much more. libguestfs can access nearly any type of filesystem including: all known types of Linux filesystem (ext2/3/4, XFS, btrfs, etc.), any Windows filesystem (VFAT and NTFS), any Mac OS X and BSD filesystems, LVM2 volumes, MBR and GPT disk partitions, raw disks, qcow2, CD and DVD ISO images, SD cards, and dozens more. libguestfs doesn't need root permissions.
Virt-df is a df implementation for virtual guests. The program is meant to be run on the host or dom0 to display disk space used and available on all partitions within all guests. There is no need to run any software or agent inside the guests. It is compatible with most Linux and Windows guests.
The Logic File System enables the user to access files through an additionnal mountpoint, /lfs, where powerful logic queries can be issued and navigation can be done through different dimensions, like date, size, or extension. For instance, LFS allows the user to perform the following commands in the shell: "cd /lfs/ext:mp3|ext:ogg/year:1973/genre:Disco/" and "ls artist:BeeGees/ artist:DonnaSummer/ artist:Chic/".