Of course, @fit and @current_number should be persistent during live migration.
you can drop RCU and @current_number,
and @fit could be exactly recreated on target side from
-device nvdim ...
set of options, which must include all currently present
(including hotplugged) devices from source side.
It's sufficient to invalidate and restart DMA transfer in flight.
i.e.
pc_dimm_memory_plug ()
-> regenerate_fit()
-> set local flag @fit-dirty
-> start QEMU.fit_read()
-> if offset == 0 ? clear @fit-dirty
make sure fit_read() won't conflict with regenerate_fit()
either plain mutex or RCU would do the job
...
OSPM.rfit()
...
if (@fit-dirty)
abort/restart DMA from start
In migration case, the target would have @fit-dirty set thanks to
pc_dimm_memory_plug () -> regenerate_fit() and any DMA in flight
would be restarted.
That's a little bit inefficient as source_fit exactly matches
target_fit and DMA could continue, but it would save us from
having fit specific migration state to transfer and maintain.