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? Thanks Eric > > 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 >
