Hmmm, interesting project: libguestfs. Back when Windows VMs were more a daily part of my life, I might have really had a use for this; now I’m just sort of curious about it.

From the description:

libguestfs is a set of tools for accessing and modifying virtual machine (VM) disk images… 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 volume management, MBR and GPT disk partitions, raw disks, qcow2, VirtualBox VDI, VMWare VMDK, CD and DVD ISOs, SD cards, and dozens more.

my first thought was that they had integrated a whole lot of libraries to support reading filesystems from disk images, layered perhaps on top of some libraries to support reading the various disk image formats. But they actually use a sorta more interesting approach: they use qemu to boot a little VM that attaches the target disk image and then acts as a server with which the library communicates to do its things. I assume (haven’t verified) that the little VM is based on a Linux kernel, for which drivers are available for a lot of that stuff. ‘course, depending on how abstract you want to be, you could consider the two approaches to be the same, with different meanings of the term ‘libraries’ and different sorts of layering. Anyway, it’s an approach I’ll have to keep in the back of my mind in case there are other problems where it can be applied…

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