device: 0.178
other: 0.155
semantic: 0.143
graphic: 0.106
PID: 0.063
debug: 0.061
network: 0.059
performance: 0.058
permissions: 0.037
vnc: 0.036
socket: 0.033
boot: 0.032
files: 0.026
KVM: 0.012
PID: 0.204
debug: 0.160
device: 0.136
other: 0.113
files: 0.081
semantic: 0.049
socket: 0.042
boot: 0.041
network: 0.040
performance: 0.039
KVM: 0.027
graphic: 0.024
permissions: 0.023
vnc: 0.020

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.