Re: device compatibility interface for live migration with assigned devices

On Wed, Aug 19, 2020 at 11:50:21AM -0600, Alex Williamson wrote: <...> > > > > > What I care about is that we have a *standard* userspace API for > > > > > performing device compatibility checking / state migration, for use by > > > > > QEMU/libvirt/ OpenStack, such that we can write code without countless > > > > > vendor specific code paths. > > > > > > > > > > If there is vendor specific stuff on the side, that's fine as we can > > > > > ignore that, but the core functionality for device compat / migration > > > > > needs to be standardized. > > > > > > > > To summarize: > > > > - choose one of sysfs or devlink > > > > - have a common interface, with a standardized way to add > > > > vendor-specific attributes > > > > ? > > > > > > Please refer to my previous email which has more example and details. > > hi Parav, > > the example is based on a new vdpa tool running over netlink, not based > > on devlink, right? > > For vfio migration compatibility, we have to deal with both mdev and physical > > pci devices, I don't think it's a good idea to write a new tool for it, given > > we are able to retrieve the same info from sysfs and there's already an > > mdevctl from Alex (https://github.com/mdevctl/mdevctl). > > > > hi All, > > could we decide that sysfs is the interface that every VFIO vendor driver > > needs to provide in order to support vfio live migration, otherwise the > > userspace management tool would not list the device into the compatible > > list? > > > > if that's true, let's move to the standardizing of the sysfs interface. > > (1) content > > common part: (must) > > - software_version: (in major.minor.bugfix scheme) > > - device_api: vfio-pci or vfio-ccw ... > > - type: mdev type for mdev device or > > a signature for physical device which is a counterpart for > > mdev type. > > > > device api specific part: (must) > > - pci id: pci id of mdev parent device or pci id of physical pci > > device (device_api is vfio-pci) > > As noted previously, the parent PCI ID should not matter for an mdev > device, if a vendor has a dependency on matching the parent device PCI > ID, that's a vendor specific restriction. An mdev device can also > expose a vfio-pci device API without the parent device being PCI. For > a physical PCI device, shouldn't the PCI ID be encompassed in the > signature? Thanks, > you are right. I need to put the PCI ID as a vendor specific field. I didn't do that because I wanted all fields in vendor specific to be configurable by management tools, so they can configure the target device according to the value of a vendor specific field even they don't know the meaning of the field. But maybe they can just ignore the field when they can't find a matching writable field to configure the target.

> > - subchannel_type (device_api is vfio-ccw) > > > > vendor driver specific part: (optional) > > - aggregator > > - chpid_type > > - remote_url > > > > NOTE: vendors are free to add attributes in this part with a > > restriction that this attribute is able to be configured with the same > > name in sysfs too. e.g. > > for aggregator, there must be a sysfs attribute in device node > > /sys/devices/pci0000:00/0000:00:02.0/882cc4da-dede-11e7-9180-078a62063ab1/intel_vgpu/aggregator, > > so that the userspace tool is able to configure the target device > > according to source device's aggregator attribute. > > > > > > (2) where and structure > > proposal 1: > > |- [path to device] > > |--- migration > > | |--- self > > | | |-software_version > > | | |-device_api > > | | |-type > > | | |-[pci_id or subchannel_type] > > | | |-<aggregator or chpid_type> > > | |--- compatible > > | | |-software_version > > | | |-device_api > > | | |-type > > | | |-[pci_id or subchannel_type] > > | | |-<aggregator or chpid_type> > > multiple compatible is allowed. > > attributes should be ASCII text files, preferably with only one value > > per file. > > > > > > proposal 2: use bin_attribute. > > |- [path to device] > > |--- migration > > | |--- self > > | |--- compatible > > > > so we can continue use multiline format. e.g. > > cat compatible > > software_version=0.1.0 > > device_api=vfio_pci > > type=i915-GVTg_V5_{val1:int:1,2,4,8} > > pci_id=80865963 > > aggregator={val1}/2 > > > > Thanks > > Yan > > >