Inspecting qcow2 volumes for integrity?

[iwelch]

A while ago, I managed to corrupt a linux guest OS. I would like to inspect its old qcow2 file now --- possibly itself corrupt, not sure --- to understand what went wrong and rescue a few files on it.

Hence, I created a new ubuntu 24.04 guest and confirmed that it could boot. Next, I was importing my old qcow2 as a new virtio device in settings (as read-only, too), and then start up my guest. it starts rolling, I select "recovery mode", I see the "EFI stub: Exiting boot services" / "loading initial ramdisk" , and then nothing else happens until I remove the old qcow2 image. I am naturally not trying to mount this qcow2 file (yet) from the guest. its very presence stops the full boot but not the bootstrap of 24.04.

I am wondering if the qcow2 file could have been corrupted (perhaps through a sloppy and unfortunate midway shutdown), but I don't know how I would even validate its integrity. I also don't really understand how it would cold-stop the guest boot, unless the guest probes for further devices, and UTM at this point never responds.

Advice appreciated.

[iwelch]

turns out that there is something more deeply wrong. even a correct qcow2 image, when imported as aa second virtio device, stops ubuntu 24.04 LTS from booting (after "exiting boot services").