Re: virtio-pci reset option

[Ani Sinha <ani@anisinha.ca>]

On Thu, Apr 1, 2021 at 7:23 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Thu, Apr 01, 2021 at 05:09:23PM +0530, Ani Sinha wrote:
> > Hi MST:
> >
> > ref: https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-bus-pci
> >
> > What: /sys/bus/pci/devices/.../reset
> > Date: July 2009
> > Contact: Michael S. Tsirkin <mst@redhat.com>
> > Description:
> > Some devices allow an individual function to be reset
> > without affecting other functions in the same device.
> > For devices that have this support, a file named reset
> > will be present in sysfs.  Writing 1 to this file
> > will perform reset.
> >
> >
> > Can you please tell me which change in the kernel virtio-pci driver
> > enabled this option to be available in sysfs? The kernel we are
> > running does not seem to have this option for virtio-pci devices. I
> > cannot seem to pin-point the exact change that is needed to get this.
> >
> >
> > thanks
> >
> > ani
>
> Likely this one:
>
> commit eb1556c493d8abc5bfc8685561bcea934700e200
> Author: Julia Suvorova <jusual@redhat.com>
> Date:   Tue Aug 20 18:30:05 2019 +0200
>
>     virtio-pci: Add Function Level Reset support

Hmm. Ok. I was actually looking in the kernel virtio-driver code
because I saw, under the same hypervisor, qemu 4.2.1, my centos 7.9 VM
was NOT showing that file in sysfs whereas my centos 8.0 did provide
that option. I was thinking, maybe the newer driver code is
responsible. Now I realize that FLR is pcie specific feature and that
my centos 8 VM is actually q35 based whereas my centos 7 VM is i440fx.
Hence, the difference.

Maybe you can consider updating that kernel documentation to mention
that this sysfs specific option is only available in PCIE and in case
of qemu based VMs, for q35 machine types.


>
>
>
> --
> MST
>