On Wed, Sep 29 2021, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote: >> From: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> >> Sent: Wednesday, September 29, 2021 10:44 AM >> >> > One alternative option is to arrange device nodes in sub-directories based >> > on the device type. But doing so also adds one trouble to userspace. The >> > current vfio uAPI is designed to have the user query device type via >> > VFIO_DEVICE_GET_INFO after opening the device. With this option the user >> > instead needs to figure out the device type before opening the device, to >> > identify the sub-directory. >> >> Wouldn't this be up to the operator / configuration, rather than the >> actual software though? I would assume that typically the VFIO >> program would be pointed at a specific vfio device node file to use, >> e.g. >> my-vfio-prog -d /dev/vfio/pci/0000:0a:03.1 >> >> Or more generally, if you're expecting userspace to know a name in a >> uniqu pattern, they can equally well know a "type/name" pair. >> > > You are correct. Currently: > > -device, vfio-pci,host=DDDD:BB:DD.F > -device, vfio-pci,sysfdev=/sys/bus/pci/devices/ DDDD:BB:DD.F > -device, vfio-platform,sysdev=/sys/bus/platform/devices/PNP0103:00 > > above is definitely type/name information to find the related node. > > Actually even for Jason's proposal we still need such information to > identify the sysfs path. > > Then I feel type-based sub-directory does work. Adding another link > to sysfs sounds unnecessary now. But I'm not sure whether we still > want to create /dev/vfio/devices/vfio0 thing and related udev rule > thing that you pointed out in another mail. Still reading through this whole thread, but type-based subdirectories also make the most sense to me. I don't really see userspace wanting to grab just any device and then figure out whether it is the device it was looking for, but rather immediately go to a specific device or at least a device of a specific type. Sequentially-numbered devices tend to become really unwieldy in my experience if you are working on a system with loads of devices.
