LVM operations can take significant amount of time. This is especially
visible when stopping a VM (`vm.storage.stop()`) - in that time the
whole qubesd freeze for about 2 seconds.
Fix this by making all the ThinVolume methods a coroutines (where
supported). Each public coroutine is also wrapped with locking on
volume._lock to avoid concurrency-related problems.
This all also require changing internal helper functions to
coroutines. There are two functions that still needs to be called from
non-coroutine call sites:
- init_cache/reset_cache (initial cache fill, ThinPool.setup())
- qubes_lvm (ThinVolume.export()
So, those two functions need to live in two variants. Extract its common
code to separate functions to reduce code duplications.
FixesQubesOS/qubes-issues#4283
b65fdf9700