Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver

[Kirti Wankhede]

On 8/10/2016 12:30 AM, Alex Williamson wrote:
> On Thu, 4 Aug 2016 00:33:51 +0530
> Kirti Wankhede <address@hidden> wrote:
> 
> This is used later by mdev_device_start() and mdev_device_stop() to get
> the parent_device so it can call the start and stop ops callbacks
> respectively.  That seems to imply that all of instances for a given
> uuid come from the same parent_device.  Where is that enforced?  I'm
> still having a hard time buying into the uuid+instance plan when it
> seems like each mdev_device should have an actual unique uuid.
> Userspace tools can figure out which uuids to start for a given user, I
> don't see much value in collecting them to instances within a uuid.
> 

Initially we started discussion with VM_UUID+instance suggestion, where
instance was introduced to support multiple devices in a VM.
'mdev_create' creates device and 'mdev_start' is to commit resources of
all instances of similar devices assigned to VM.

For example, to create 2 devices:
# echo "$UUID:0:params" > /sys/devices/../mdev_create
# echo "$UUID:1:params" > /sys/devices/../mdev_create

"$UUID-0" and "$UUID-1" devices are created.

Commit resources for above devices with single 'mdev_start':
# echo "$UUID" > /sys/class/mdev/mdev_start

Considering $UUID to be a unique UUID of a device, we don't need
'instance', so 'mdev_create' would look like:

# echo "$UUID1:params" > /sys/devices/../mdev_create
# echo "$UUID2:params" > /sys/devices/../mdev_create

where $UUID1 and $UUID2 would be mdev device's unique UUID and 'params'
would be vendor specific parameters.

Device nodes would be created as "$UUID1" and "$UUID"

Then 'mdev_start' would be:
# echo "$UUID1, $UUID2" > /sys/class/mdev/mdev_start

Similarly 'mdev_stop' and 'mdev_destroy' would be:

# echo "$UUID1, $UUID2" > /sys/class/mdev/mdev_stop

and

# echo "$UUID1" > /sys/devices/../mdev_destroy
# echo "$UUID2" > /sys/devices/../mdev_destroy

Does this seems reasonable?

Thanks,
Kirti