Re: [PATCH v9 02/10] admin: introduce device group and related concepts

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Nov 24, 2022 at 01:41:41PM +0800, Jason Wang wrote:
> On Thu, Nov 24, 2022 at 5:08 AM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > Each device group has a type. For now, define one initial group:
> >
> > SR-IOV type - PCI SR-IOV virtual functions (VFs) of a given
> > PCI SR-IOV physical function (PF). This group may contain one or more
> > virtio devices.
> >
> > Each device within a group has a unique identifier. This identifier
> > is the group member identifier.
> >
> > Note: one can argue both ways whether the new device group handling
> > functionality (this and following patches) is closer
> > to a new device type or a new transport type.
> >
> > However, I expect that we will add more features in the near future. To
> > facilitate this as much as possible of the text is located in the new
> > admin chapter.
> >
> > I did my best to minimize transport-specific text.
> >
> > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> >  admin.tex   | 45 +++++++++++++++++++++++++++++++++++++++++++++
> >  content.tex |  2 ++
> >  2 files changed, 47 insertions(+)
> >  create mode 100644 admin.tex
> >
> > diff --git a/admin.tex b/admin.tex
> > new file mode 100644
> > index 0000000..6ebdd05
> > --- /dev/null
> > +++ b/admin.tex
> > @@ -0,0 +1,45 @@
> > +\section{Device groups}\label{sec:Basic Facilities of a Virtio Device / Device groups}
> > +
> > +It is occasionally useful to have a device control a group of
> > +other devices. Terminology used in such cases:
> > +
> > +\begin{description}
> > +\item[Device group]
> > +        or just group, includes zero or more devices.
> > +\item[Owner device]
> > +        or owner, the device controlling the group.
> > +\item[Member device]
> > +        a device within a group. The owner device itself is not
> > +       a member of the group.
> > +\item[Member identifier]
> > +        each member has this identifier, unique within the group
> > +       and used to address it through the owner device.
> > +\item[Group type identifier]
> > +       specifies what kind of member devices there are in a
> > +       group, how is the member identifier is interpreted
> > +       and what kind of control the owner has.
> > +       A given owner can control a single group of a given type,
> > +       thus the type and the owner together identify the group.
> > +\end{description}
> > +
> > +The following group types, and their identifiers, are currently specified):
> > +\begin{description}
> > +\item[SR-IOV group type (0x1)]
> > +This device group has a PCI Single Root I/O Virtualization
> > +(SR-IOV) physical function (PF) device as the owner and includes
> > +all its SR-IOV virtual functions (VFs) as members (see
> > +\hyperref[intro:PCIe]{[PCIe]}).
> 
> So I wonder what's the advantage of using a global identifier over the
> transport specific one. There's almost no way for CCW/MMIO to use
> SR-IOV. Limiting it to PCI seems much easier and avoids layer
> violation.
> 
> Thanks

So we burn up an identifier, ccw and mmio won't be able to use it.
Big deal? Why? And I think we might find a use for this with MMIO
down the road with some kind of passthrough. Who knows.



> > +
> > +The PF device itself is not a member of the group.
> > +
> > +The group type identifier for this group is 0x1.
> > +
> > +A member identifier for this group can have a value 0x1 to 0xFFFF
> > +and equals the SR-IOV VF number of the member device (see
> > +\hyperref[intro:PCIe]{[PCIe]}).
> > +
> > +Both owner and member devices for this group type use the Virtio
> > +PCI transport (see \ref{sec:Virtio Transport Options / Virtio Over PCI Bus}).
> > +\end{description}
> > +
> > +
> > diff --git a/content.tex b/content.tex
> > index e3203be..3f3585d 100644
> > --- a/content.tex
> > +++ b/content.tex
> > @@ -491,6 +491,8 @@ \section{Exporting Objects}\label{sec:Basic Facilities of a Virtio Device / Expo
> >  types. It is RECOMMENDED that devices generate version 4
> >  UUIDs as specified by \hyperref[intro:rfc4122]{[RFC4122]}.
> >
> > +\input{admin.tex}
> > +
> >  \chapter{General Initialization And Device Operation}\label{sec:General Initialization And Device Operation}
> >
> >  We start with an overview of device initialization, then expand on the
> > --
> > MST
> >