Re: [PATCH v3 00/10] rust: pci: add abstractions for SR-IOV capability

[Leon Romanovsky <leon@kernel.org>]

On Wed, Mar 04, 2026 at 03:57:57PM +0100, Danilo Krummrich wrote:
> On Wed Mar 4, 2026 at 3:26 PM CET, Leon Romanovsky wrote:
> > On Wed, Mar 04, 2026 at 10:18:52AM -0400, Jason Gunthorpe wrote:
> >> On Wed, Mar 04, 2026 at 10:47:50AM +0200, Leon Romanovsky wrote:
> >> > On Tue, Mar 03, 2026 at 04:15:20PM -0500, Peter Colberg wrote:
> >> > > Add Rust abstractions for the Single Root I/O Virtualization (SR-IOV)
> >> > > capability of a PCI device. Provide a minimal set of wrappers for the
> >> > > SR-IOV C API to enable and disable SR-IOV for a device, and query if
> >> > > a PCI device is a Physical Function (PF) or Virtual Function (VF).
> >> > 
> >> > <...>
> >> > 
> >> > > For PF drivers written in C, disabling SR-IOV on remove() may be opted
> >> > > into by setting the flag managed_sriov in the pci_driver structure. For
> >> > > PF drivers written in Rust, disabling SR-IOV on unbind() is mandatory.
> >> > 
> >> > Why? Could you explain the rationale behind this difference between C and
> >> > Rust? Let me remind you that SR‑IOV devices which do not disable VFs do so
> >> > for a practical and well‑established reason: maximizing hardware
> >> > utilization.
> >> 
> >> Personally I think drivers doing this are wrong. That such a driver
> >> bug was allowed to become UAPI is pretty bad. The rust approach is
> >> better.
> >
> > We already had this discussion. I see this as a perfectly valid
> > use-case.
> 
> Can you remind about a specific use-case for this please? (Ideally, one that
> can't be solved otherwise.)

You create X VFs through sriov_configure, unbind PF, bind it to vfio
instead and forward (X + 1) functions to different VMs.

If you destroy VFs on PF unbind, you will find yourself with one
function less per-device, as you will have not-utilized PF now,
which consumes HW resources anyway.

Thanks