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. You can look at this for some general over engineered code to handle opening from a sysfs handle like above: https://github.com/linux-rdma/rdma-core/blob/master/util/open_cdev.c Jason
