Re: [PATCH v4] vfio/pci: print vfio-device syspath to fdinfo

[Cédric Le Goater <clg@xxxxxxxx>]

On 8/8/25 17:45, Amit Machhiwal wrote:
> Hi Cédric,
>
> Please find my comments inline:
>
> On 2025/08/08 03:49 PM, Cédric Le Goater wrote:
> > Hello Amit,
> >
> > On 8/7/25 11:34, Amit Machhiwal wrote:
> > > Hello,
> > >
> > > On 2025/08/04 12:44 PM, Alex Mastro wrote:
> > > > Print the PCI device syspath to a vfio device's fdinfo. This enables tools
> > > > to query which device is associated with a given vfio device fd.
> > > >
> > > > This results in output like below:
> > > >
> > > > $ cat /proc/"$SOME_PID"/fdinfo/"$VFIO_FD" | grep vfio
> > > > vfio-device-syspath: /sys/devices/pci0000:e0/0000:e0:01.1/0000:e1:00.0/0000:e2:05.0/0000:e8:00.0
> > > >
> > > > Signed-off-by: Alex Mastro <amastro@xxxxxx>
> > >
> > > I tested this patch on a POWER9 bare metal system with a VFIO PCI device and
> > > could see the VFIO device syspath in fdinfo.
> >
> > POWER9 running on OPAL FW : I am curious about the software stack.
> >
> > I suppose this is the latest upstream kernel ?
>
> Yes, I used the latest upstream kernel and applied this patch on top of commit
> cca7a0aae895.
>
> > Are you using an upstream QEMU to test too ?
>
> No, I had used the Fedora 42 distro qemu. The version details are as below:
>
>    [root@localhost ~]# qemu-system-ppc64 --version
>    QEMU emulator version 9.2.4 (qemu-9.2.4-1.fc42)
>    Copyright (c) 2003-2024 Fabrice Bellard and the QEMU Project developers
>
> I gave the upstream qemu (HEAD pointing to cd21ee5b27) a try and I see the same
> behavior with that too.
>
>    [root@localhost ~]# ./qemu-system-ppc64 --version
>    QEMU emulator version 10.0.92 (v10.1.0-rc2-4-gcd21ee5b27-dirty)
>    Copyright (c) 2003-2025 Fabrice Bellard and the QEMU Project developers
>
>    [root@localhost ~]# cat /proc/52807/fdinfo/191
>    pos:    0
>    flags:  02000002
>    mnt_id: 17
>    ino:    1125
>    vfio-device-syspath: /sys/devices/pci0031:00/0031:00:00.0/0031:01:00.0
>
> > and which device ?
>
> I'm using a Broadcom NetXtreme network card (4-port) and passing through its
> fn0.
>
>    [root@guest ~]# lspci
>    [...]
>    0001:00:01.0 Ethernet controller: Broadcom Inc. and subsidiaries NetXtreme BCM5719 Gigabit Ethernet PCIe (rev 01)
>
> Please let me know if I may help you with any additional information.

It is good to know that device pass-through still works with upstream on
OpenPower servers.

Have you tried VFs ?

Thanks Amit,

C.