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

[Neo Jia]

On Tue, Aug 16, 2016 at 12:30:25AM +0000, Tian, Kevin wrote:
> > From: Neo Jia [mailto:address@hidden
> > Sent: Tuesday, August 16, 2016 3:59 AM

> > > >
> > > > For NVIDIA vGPU solution we need to know all devices assigned to a VM in
> > > > one shot to commit resources of all vGPUs assigned to a VM along with
> > > > some common resources.
> > >
> > > Kirti, can you elaborate the background about above one-shot commit
> > > requirement? It's hard to understand such a requirement.
> > >
> > > As I relied in another mail, I really hope start/stop become a per-mdev
> > > attribute instead of global one, e.g.:
> > >
> > > echo "0/1" > /sys/class/mdev/12345678-1234-1234-1234-123456789abc/start
> > >
> > > In many scenario the user space client may only want to talk to mdev
> > > instance directly, w/o need to contact its parent device. Still take
> > > live migration for example, I don't think Qemu wants to know parent
> > > device of assigned mdev instances.
> > 
> > Hi Kevin,
> > 
> > Having a global /sys/class/mdev/mdev_start doesn't require anybody to know
> > parent device. you can just do
> > 
> > echo "mdev_UUID" > /sys/class/mdev/mdev_start
> > 
> > or
> > 
> > echo "mdev_UUID" > /sys/class/mdev/mdev_stop
> > 
> > without knowing the parent device.
> > 
> 
> You can look at some existing sysfs example, e.g.:
> 
> echo "0/1" > /sys/bus/cpu/devices/cpu1/online
> 
> You may also argue why not using a global style:
> 
> echo "cpu1" > /sys/bus/cpu/devices/cpu_online
> echo "cpu1" > /sys/bus/cpu/devices/cpu_offline
> 
> There are many similar examples...

Hi Kevin,

My response above is to your question about using the global sysfs entry as you
don't want to have the global path because

"I don't think Qemu wants to know parent device of assigned mdev instances.".

So I just want to confirm with you that (in case you miss):

    /sys/class/mdev/mdev_start | mdev_stop 

doesn't require the knowledge of parent device.

Thanks,
Neo

> 
> Thanks
> Kevin