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Re: device compatibility interface for live migration with assigned devices




On 2020/8/18 下午4:55, Daniel P. Berrangé wrote:
On Tue, Aug 18, 2020 at 11:24:30AM +0800, Jason Wang wrote:
On 2020/8/14 下午1:16, Yan Zhao wrote:
On Thu, Aug 13, 2020 at 12:24:50PM +0800, Jason Wang wrote:
On 2020/8/10 下午3:46, Yan Zhao wrote:
driver is it handled by?
It looks that the devlink is for network device specific, and in
devlink.h, it says
include/uapi/linux/devlink.h - Network physical device Netlink
interface,
Actually not, I think there used to have some discussion last year and the
conclusion is to remove this comment.

It supports IB and probably vDPA in the future.

hmm... sorry, I didn't find the referred discussion. only below discussion
regarding to why to add devlink.

https://www.mail-archive.com/netdev vger kernel org/msg95801.html
	>This doesn't seem to be too much related to networking? Why can't something
	>like this be in sysfs?
	
	It is related to networking quite bit. There has been couple of
	iteration of this, including sysfs and configfs implementations. There
	has been a consensus reached that this should be done by netlink. I
	believe netlink is really the best for this purpose. Sysfs is not a good
	idea
See the discussion here:

https://patchwork.ozlabs.org/project/netdev/patch/20191115223355 1277139-1-jeffrey t kirsher intel com/


https://www.mail-archive.com/netdev vger kernel org/msg96102.html
	>there is already a way to change eth/ib via
	>echo 'eth' > /sys/bus/pci/drivers/mlx4_core/0000:02:00.0/mlx4_port1
	>
	>sounds like this is another way to achieve the same?
	
	It is. However the current way is driver-specific, not correct.
	For mlx5, we need the same, it cannot be done in this way. Do devlink is
	the correct way to go.

https://lwn.net/Articles/674867/
	There a is need for some userspace API that would allow to expose things
	that are not directly related to any device class like net_device of
	ib_device, but rather chip-wide/switch-ASIC-wide stuff.

	Use cases:
	1) get/set of port type (Ethernet/InfiniBand)
	2) monitoring of hardware messages to and from chip
	3) setting up port splitters - split port into multiple ones and squash again,
	   enables usage of splitter cable
	4) setting up shared buffers - shared among multiple ports within one chip



we actually can also retrieve the same information through sysfs, .e.g

|- [path to device]
   |--- migration
   |     |--- self
   |     |   |---device_api
   |	|   |---mdev_type
   |	|   |---software_version
   |	|   |---device_id
   |	|   |---aggregator
   |     |--- compatible
   |     |   |---device_api
   |	|   |---mdev_type
   |	|   |---software_version
   |	|   |---device_id
   |	|   |---aggregator

Yes but:

- You need one file per attribute (one syscall for one attribute)
- Attribute is coupled with kobject

All of above seems unnecessary.

Another point, as we discussed in another thread, it's really hard to make
sure the above API work for all types of devices and frameworks. So having a
vendor specific API looks much better.
From the POV of userspace mgmt apps doing device compat checking / migration,
we certainly do NOT want to use different vendor specific APIs. We want to
have an API that can be used / controlled in a standard manner across vendors.


Yes, but it could be hard. E.g vDPA will chose to use devlink (there's a long debate on sysfs vs devlink). So if we go with sysfs, at least two APIs needs to be supported ...

Thanks





Regards,
Daniel

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