Prior to this commit, there have been occasional issues with the usage
of the Qubes Manager's VM restart button where the restart procedure
is interrupted due to an exception thrown after the VM in question is
shut down. The exception has the following backtrace:
----
line: assert not vm.is_running()
func: start_vm
line no.: 1198
file: /usr/lib64/python2.7/site-packages/qubesmanager/main.py
----
line: self.caller.start_vm(vm)
func: check_if_vm_has_shutdown
line no.: 308
file: /usr/lib64/python2.7/site-packages/qubesmanager/main.py
Upon investigation, the root cause of the issue appears to be
inconsistent information provided by Xen regarding a recently-shut-down
VM's start-up timestamp and its state (i.e., running or shut down).
In some cases Xen would report that the VM is running whereas the
start-up timestamp would be returned as None, due to unknown reasons.
This inconsistency would then cause the code modified by this commit to
call the Qubes Manager's "start_vm" method, which would attempt to
assert that a VM is shut down, which would raise the aforementioned
exception.
This commit aims to resolve this issue by checking whether the VM has
fully shut down according to Xen and by calling "start_vm" only if the
VM has fully shut down.
This commit also slightly refactors the affected code.
Fixes: QubesOS/qubes-issues#2438
d551bdc3fa