On Tue, Sep 21, 2021 at 10:00:14PM -0300, 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 thought part of the appeal of the device centric model was less grovelling around in sysfs for information. Using type/address directly in /dev seems simpler than having to dig around matching things here. Note that this doesn't have to be done in kernel: you could have the kernel just call them /dev/vfio/devices/vfio0, ... but add udev rules that create symlinks from say /dev/vfio/pci/DDDD:BB:SS.F - > ../devices/vfioXX based on the sysfs information. > > 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 > -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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