Created attachment 678826 [details]
~/.cache/libvirt/qemu/log/boxes-unknown-2.log

Apparently you can just close gnome-boxes while a vm is running in it and it
should save the state of the running machine to disk for future use. When boxes
is started thereafter and one starts the vm again, it should resume from its
saved state. Instead boxes complains "resuming from saved state failed. Try to
restart?" and upon clicking "OK" the vm boots from fresh losing all saved info
in the process. The following is what is printed to the journal during a
typical boxes -> close and restart session:

May 30 15:30:08 mal libvirtd[20082]: operation failed: job: unexpectedly failed
May 30 15:30:08 mal virtlogd[20254]: libvirt version: 1.3.4
May 30 15:30:08 mal virtlogd[20254]: hostname: mal.xxx
May 30 15:30:08 mal virtlogd[20254]: End of file while reading data:
Input/output error
May 30 15:30:08 mal virtlogd[20254]: Cannot open log file:
'/home/atri/.cache/libvirt/qemu/log/boxes-unknown-2.log': Device or resource
busy
May 30 15:30:08 mal libvirtd[20082]: Cannot open log file:
'/home/atri/.cache/libvirt/qemu/log/boxes-unknown-2.log': Device or resource
busy
May 30 15:30:08 mal virtlogd[20254]: End of file while reading data:
Input/output error
May 30 15:30:08 mal libvirtd[20082]: Unable to restore from managed state
/home/atri/.config/libvirt/qemu/save/boxes-unknown-2.save. Maybe the file is
corrupted?

The log file in question exists and is very much readable. E.g.: see attached
log file.