Re: [RFC 0/4] Enable virtio-fs on s390x

[Stefan Hajnoczi]

On Mon, Jun 29, 2020 at 02:07:16PM +0100, Daniel P. Berrangé wrote:
> On Mon, Jun 29, 2020 at 01:53:05PM +0100, Stefan Hajnoczi wrote:
> > On Thu, Jun 25, 2020 at 12:04:26PM +0200, Marc Hartmayer wrote:
> > > This RFC is about enabling virtio-fs on s390x. For that we need
> > >  + some shim code (first patch), and we need
> > >  + libvhost-user to deal with virtio endiannes as mandated by the spec.
> > >  
> > > The second part is trickier, because unlike QEMU we are not certain
> > > about the guest's native endianness, which is needed to handle the
> > > legacy-interface appropriately. In fact, this is the reason why just
> > > RFC.
> > > 
> > > One of the open questions is whether to build separate versions, one
> > > for guest little endian and one for guest big endian, or do we want
> > > something like a command line option? (Digression on the libvirt
> > > modeling)
> > > 
> > > A third option would be to refuse legacy altogether.
> > 
> > I suggest the following:
> > 
> > 1. Combinations that worked with libvhost-user in the past must not break.
> > 
> > 2. New combinations should only support VIRTIO 1.0 and later.
> > 
> > This means continue to allow Legacy mode devices where they already run
> > today but don't add new code for the cases that didn't work.
> 
> What I'm missing here is what PCI product ID was being used when the
> current impl is in legacy/transitional mode ?
> 
> Normally legacy and transitional mode devices need an explicit PCI ID
> reserved, where as modern-only devices have a PCI ID derived from their
> VirtIO ID + a fixed offset.
> 
> Was this mistakenly using a VirtIO ID + fixed offset for the legacy
> mode too ?

vhost-user-fs-pci does not support Legacy or Transitional mode. See
hw/virtio/vhost-user-fs-pci.c:

  static const VirtioPCIDeviceTypeInfo vhost_user_fs_pci_info = {
      .base_name             = TYPE_VHOST_USER_FS_PCI,
      .non_transitional_name = "vhost-user-fs-pci",
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      .instance_size = sizeof(VHostUserFSPCI),
      .instance_init = vhost_user_fs_pci_instance_init,
      .class_init    = vhost_user_fs_pci_class_init,
  };

Stefan

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