VFIO/vfio-user: specify NVMe namespace to boot from

[Thanos Makatos]

We're working on implementing a virtual NVMe controller based on SPDK and a 
multiprocess-qemu branch that uses the vfio-user. We're facing a problem where 
the existing API doesn't allow us to tell QEMU from which NVMe namespace we'd 
like SeaBIOS to boot from.

How can we solve this problem? Can we add a parameter to the '-boot' option, 
e.g. '-boot path=/devices/pciblah/...@namespace0'? AFAIK VFIO should have the 
same problem. 

The corresponding SeaBIOS patch can be found in 
https://mail.coreboot.org/hyperkitty/list/seabios@seabios.org/thread/2Q7NPH7TJNHK6JGPHQL7755HILO23ISN/