Re: device compatibility interface for live migration with assigned devices

[Jason Wang]

On 2020/7/18 上午12:12, Alex Williamson wrote:
> On Thu, 16 Jul 2020 16:32:30 +0800
> Yan Zhao <yan.y.zhao@intel.com> wrote:
>
> > On Thu, Jul 16, 2020 at 12:16:26PM +0800, Jason Wang wrote:
> > > On 2020/7/14 上午7:29, Yan Zhao wrote:
> > > > hi folks,
> > > > we are defining a device migration compatibility interface that helps upper
> > > > layer stack like openstack/ovirt/libvirt to check if two devices are
> > > > live migration compatible.
> > > > The "devices" here could be MDEVs, physical devices, or hybrid of the two.
> > > > e.g. we could use it to check whether
> > > > - a src MDEV can migrate to a target MDEV,
> > > > - a src VF in SRIOV can migrate to a target VF in SRIOV,
> > > > - a src MDEV can migration to a target VF in SRIOV.
> > > >     (e.g. SIOV/SRIOV backward compatibility case)
> > > >
> > > > The upper layer stack could use this interface as the last step to check
> > > > if one device is able to migrate to another device before triggering a real
> > > > live migration procedure.
> > > > we are not sure if this interface is of value or help to you. please don't
> > > > hesitate to drop your valuable comments.
> > > >
> > > >
> > > > (1) interface definition
> > > > The interface is defined in below way:
> > > >
> > > >                __    userspace
> > > >                 /\              \
> > > >                /                 \write
> > > >               / read              \
> > > >      ________/__________       ___\|/_____________
> > > >     | migration_version |     | migration_version |-->check migration
> > > >     ---------------------     ---------------------   compatibility
> > > >        device A                    device B
> > > >
> > > >
> > > > a device attribute named migration_version is defined under each device's
> > > > sysfs node. e.g. 
> > > > (/sys/bus/pci/devices/0000\:00\:02.0/$mdev_UUID/migration_version).
> > >
> > > Are you aware of the devlink based device management interface that is
> > > proposed upstream? I think it has many advantages over sysfs, do you
> > > consider to switch to that?
>
> Advantages, such as?


My understanding for devlink(netlink) over sysfs (some are mentioned at 
the time of vDPA sysfs mgmt API discussion) are:

- existing users (NIC, crypto, SCSI, ib), mature and stable
- much better error reporting (ext_ack other than string or errno)
- namespace aware
- do not couple with kobject

Thanks