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Date: Thu, 23 Sep 2021 09:25:27 +0200 From: Eric Auger <eric.auger@...hat.com> To: Jason Gunthorpe <jgg@...dia.com>, "Tian, Kevin" <kevin.tian@...el.com> Cc: "Liu, Yi L" <yi.l.liu@...el.com>, "alex.williamson@...hat.com" <alex.williamson@...hat.com>, "hch@....de" <hch@....de>, "jasowang@...hat.com" <jasowang@...hat.com>, "joro@...tes.org" <joro@...tes.org>, "jean-philippe@...aro.org" <jean-philippe@...aro.org>, "parav@...lanox.com" <parav@...lanox.com>, "lkml@...ux.net" <lkml@...ux.net>, "pbonzini@...hat.com" <pbonzini@...hat.com>, "lushenming@...wei.com" <lushenming@...wei.com>, "corbet@....net" <corbet@....net>, "Raj, Ashok" <ashok.raj@...el.com>, "yi.l.liu@...ux.intel.com" <yi.l.liu@...ux.intel.com>, "Tian, Jun J" <jun.j.tian@...el.com>, "Wu, Hao" <hao.wu@...el.com>, "Jiang, Dave" <dave.jiang@...el.com>, "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>, "kwankhede@...dia.com" <kwankhede@...dia.com>, "robin.murphy@....com" <robin.murphy@....com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>, "dwmw2@...radead.org" <dwmw2@...radead.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>, "david@...son.dropbear.id.au" <david@...son.dropbear.id.au>, "nicolinc@...dia.com" <nicolinc@...dia.com> Subject: Re: [RFC 03/20] vfio: Add vfio_[un]register_device() 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@...dia.com> >>> 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 >
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