On Thu, Sep 23, 2021 at 09:25:27AM +0200, Eric Auger wrote: > Hi, > > On 9/22/21 3:00 AM, Jason Gunthorpe wrote: > > On Wed, Sep 22, 2021 at 12:54:02AM +0000, Tian, Kevin wrote: > >>> From: Jason Gunthorpe <jgg@xxxxxxxxxx> > >>> Sent: Wednesday, September 22, 2021 12:01 AM > >>> > >>>> One open about how to organize the device nodes under > >>> /dev/vfio/devices/. > >>>> This RFC adopts a simple policy by keeping a flat layout with mixed > >>> devname > >>>> from all kinds of devices. The prerequisite of this model is that devnames > >>>> from different bus types are unique formats: > >>> This isn't reliable, the devname should just be vfio0, vfio1, etc > >>> > >>> The userspace can learn the correct major/minor by inspecting the > >>> sysfs. > >>> > >>> This whole concept should disappear into the prior patch that adds the > >>> struct device in the first place, and I think most of the code here > >>> can be deleted once the struct device is used properly. > >>> > >> Can you help elaborate above flow? This is one area where we need > >> more guidance. > >> > >> When Qemu accepts an option "-device vfio-pci,host=DDDD:BB:DD.F", > >> how does Qemu identify which vifo0/1/... is associated with the specified > >> DDDD:BB:DD.F? > > When done properly in the kernel the file: > > > > /sys/bus/pci/devices/DDDD:BB:DD.F/vfio/vfioX/dev > > > > Will contain the major:minor of the VFIO device. > > > > Userspace then opens the /dev/vfio/devices/vfioX and checks with fstat > > that the major:minor matches. > > > > in the above pattern "pci" and "DDDD:BB:DD.FF" are the arguments passed > > to qemu. > I guess this would be the same for platform devices, for instance > /sys/bus/platform/devices/AMDI8001:01/vfio/vfioX/dev, right? Yes, it is the general driver core pattern for creating cdevs below a parent device Jason
