On Wed, 27 Mar 2019 16:10:20 -0600 Alex Williamson <alex.williamson@xxxxxxxxxx> wrote: > On Wed, 27 Mar 2019 20:18:54 +0000 > "Dr. David Alan Gilbert" <dgilbert@xxxxxxxxxx> wrote: > > > * Zhao Yan (yan.y.zhao@xxxxxxxxx) wrote: > > > On Wed, Feb 20, 2019 at 07:42:42PM +0800, Cornelia Huck wrote: > > > > > > > > b) How do we detect if we're migrating from/to the wrong device or > > > > > > > > version of device? Or say to a device with older firmware or perhaps > > > > > > > > a device that has less device memory ? > > > > > > > Actually it's still an open for VFIO migration. Need to think about > > > > > > > whether it's better to check that in libvirt or qemu (like a device magic > > > > > > > along with verion ?). > > > > > > > > > > We must keep the hardware generation is the same with one POD of public cloud > > > > > providers. But we still think about the live migration between from the the lower > > > > > generation of hardware migrated to the higher generation. > > > > > > > > Agreed, lower->higher is the one direction that might make sense to > > > > support. > > > > > > > > But regardless of that, I think we need to make sure that incompatible > > > > devices/versions fail directly instead of failing in a subtle, hard to > > > > debug way. Might be useful to do some initial sanity checks in libvirt > > > > as well. > > > > > > > > How easy is it to obtain that information in a form that can be > > > > consumed by higher layers? Can we find out the device type at least? > > > > What about some kind of revision? > > > hi Alex and Cornelia > > > for device compatibility, do you think it's a good idea to use "version" > > > and "device version" fields? > > > > > > version field: identify live migration interface's version. it can have a > > > sort of backward compatibility, like target machine's version >= source > > > machine's version. something like that. > > Don't we essentially already have this via the device specific region? > The struct vfio_info_cap_header includes id and version fields, so we > can declare a migration id and increment the version for any > incompatible changes to the protocol. > > > > > > > device_version field consists two parts: > > > 1. vendor id : it takes 32 bits. e.g. 0x8086. > > Who allocates IDs? If we're going to use PCI vendor IDs, then I'd > suggest we use a bit to flag it as such so we can reserve that portion > of the 32bit address space. See for example: > > #define VFIO_REGION_TYPE_PCI_VENDOR_TYPE (1 << 31) > #define VFIO_REGION_TYPE_PCI_VENDOR_MASK (0xffff) > > For vendor specific regions. Just browsing through the thread... if I don't misunderstand, we could use a vfio-ccw region type id here for ccw, couldn't we? Just to make sure that this is not pci-specific.
