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Re: [RFC 0/4] Enable virtio-fs on s390x
From: |
Michael S. Tsirkin |
Subject: |
Re: [RFC 0/4] Enable virtio-fs on s390x |
Date: |
Thu, 2 Jul 2020 06:01:02 -0400 |
On Tue, Jun 30, 2020 at 11:39:32AM +0200, Cornelia Huck wrote:
> On Tue, 30 Jun 2020 10:04:51 +0100
> Stefan Hajnoczi <stefanha@redhat.com> wrote:
>
> > 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,
> > };
>
> This makes it very unlikely that someone accidentally configures
> non-modern, but does not prevent it AFAICS. See
> <20200630113527.7b27f34f.cohuck@redhat.com>, which I just sent.
>
> (I may be off, because that is all very confusing...)
Right. We'll block legacy for modern only devices going forward.
Going back to the patchset in question, virtio-fs is modern
only, legacy will not be supported.
--
MST
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Michael S. Tsirkin <=