On Tue, Sep 10, 2019 at 11:23:50PM +0300, Toe Dev wrote: > Hey, > While reviewing I noticed maybe we need to update the spec revision. > In: nvme_class_init(...) > > current code pc->revision=2 > change to: pc->revision=3 > However not really important I think.. Just for consistency. > When I done reviewing, should it be patched too, How?
The NVMe specification declares the PCI Revision ID field implementation specific. It doesn't seem to be a reflection of the NVMe specification supported by the device. If there is a PCI Vendor 0x8086 Device 0x5845 in the real world with revision = 3 that we now emulate correctly, then it could be updated. However, for live migration compatibility QEMU must keep old guest-visible behavior too. It's not as simple as changing the revision value to 3, because then existing VMs migrating from an old QEMU to a new QEMU would suddenly see the hardware change beneath them. QEMU has the "machine types" mechanism to deal with this. QEMU 4.2 and later machine types (e.g. "pc-q35-4.2") would use revision = 3 while older machine types would use revision = 2. This maintains live migration compatibility. In summary, there is probably no strong reason to change this (although I'm not an NVMe expert so maybe I've missed something).
signature.asc
Description: PGP signature
