Linux Virtualization - Oct 2023 - [PATCH vfio 10/11] vfio/virtio: Expose admin commands over virtio device

On Tue, Oct 10, 2023 at 07:09:08PM +0300, Yishai Hadas
wrote:
> 
> > > Assuming that we'll put each command inside virtio as the
generic layer, we
> > > won't be able to call/use this API internally to get the PF
as of cyclic
> > > dependencies between the modules, link will fail.
I just mean:
virtio_admin_legacy_io_write(sruct pci_device *,  ....)


internally it starts from vf gets the pf (or vf itself or whatever
the transport is) sends command gets status returns.

what is cyclic here?

-- 
MST

On 10/10/2023 23:42, Michael S. Tsirkin wrote:
> On Tue, Oct 10, 2023 at 07:09:08PM +0300, Yishai Hadas wrote:
>>>> Assuming that we'll put each command inside virtio as the
generic layer, we
>>>> won't be able to call/use this API internally to get the PF
as of cyclic
>>>> dependencies between the modules, link will fail.
> I just mean:
> virtio_admin_legacy_io_write(sruct pci_device *,  ....)
>
>
> internally it starts from vf gets the pf (or vf itself or whatever
> the transport is) sends command gets status returns.
>
> what is cyclic here?
>
virtio-pci depends on virtio [1].

If we put the commands in the generic layer as we expect it to be (i.e. 
virtio), then trying to call internally call for 
virtio_pci_vf_get_pf_dev() to get the PF from the VF will end-up by a 
linker cyclic error as of below [2].

As of that, someone can suggest to put the commands in virtio-pci, 
however this will fully bypass the generic layer of virtio and future 
clients won't be able to use it.

In addition, passing in the VF PCI pointer instead of the VF group 
member ID + the VIRTIO PF device, will require in the future to 
duplicate each command once we'll use SIOV devices.

Instead, we suggest the below API for the above example.

virtio_admin_legacy_io_write(virtio_device *virtio_dev,? u64 
group_member_id,? ....)

[1]

[yishaih at reg-l-vrt-209 linux]$ modinfo virtio-pci
filename: /lib/modules/6.6.0-rc2+/kernel/drivers/virtio/virtio_pci.ko
version:??????? 1
license:??????? GPL
description:??? virtio-pci
author:???????? Anthony Liguori <aliguori at us.ibm.com>
srcversion:???? 7355EAC9408D38891938391
alias:????????? pci:v00001AF4d*sv*sd*bc*sc*i*
depends: virtio_pci_modern_dev,virtio,virtio_ring,virtio_pci_legacy_dev
retpoline:????? Y
intree:???????? Y
name:?????????? virtio_pci
vermagic:?????? 6.6.0-rc2+ SMP preempt mod_unload modversions
parm:?????????? force_legacy:Force legacy mode for transitional virtio 1 
devices (bool)

[2]

depmod: ERROR: Cycle detected: virtio -> virtio_pci -> virtio
depmod: ERROR: Found 2 modules in dependency cycles!
make[2]: *** [scripts/Makefile.modinst:128: depmod] Error 1
make[1]: *** [/images/yishaih/src/kernel/linux/Makefile:1821: 
modules_install] Error 2

Yishai