snapshot=on fails with non file-based storage

The snapshot=on option doesn't work with an nbd block device:

/usr/bin/qemu-system-x86_64 \
[...]
    -device virtio-scsi-pci,id=scsi \
    -drive file=nbd:localhost:61930,snapshot=on,format=raw,id=hd0,if=none \
    -device scsi-hd,drive=hd0 \
[...]

gives the error:

qemu-system-x86_64: -drive file=nbd:localhost:61930,snapshot=on,format=raw,id=hd0,if=none: could not open disk image nbd:localhost:61930: No such file or directory

If you remove the snapshot=on flag, it works (although that of course means that the block device is writable which we don't want).

Previously reported here:

  http://permalink.gmane.org/gmane.comp.emulators.qemu/148390

and I can confirm this still happens in qemu 1.4.0.

Triaging old bug tickets... I think this has likely been fixed in 2013 ... or can you still reproduce this issue with the latest version of QEMU? Could we close this ticket nowadays?

Let's close this.  libguestfs doesn't use snapshot=on any longer.