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

["Danilo Krummrich" <dakr@kernel.org>]

On Wed Mar 4, 2026 at 6:02 PM CET, Leon Romanovsky wrote:
> On Wed, Mar 04, 2026 at 12:45:51PM -0400, Jason Gunthorpe wrote:
>> On Wed, Mar 04, 2026 at 06:27:11PM +0200, Leon Romanovsky wrote:
>> > 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.
>> 
>> No, illegal, and it doesn't even work right. When VFIO FLRs the PF it
>> will blow up the half baked SRIOV and break everything.
>
> The FLR can be disabled. For example, PCI_DEV_FLAGS_NO_FLR_RESET flag
> will do it.

But this is a quirk and not a feature, no? So, we shouldn't use it as a baseline
for actual features.