Re: [virtio-dev] Re: [PATCH v10 03/10] admin: introduce group administration commands

[Jiri Pirko <jiri@nvidia.com>]

Fri, Mar 03, 2023 at 09:23:14PM CET, stefanha@redhat.com wrote:
>On Fri, Mar 03, 2023 at 08:18:43AM -0500, Michael S. Tsirkin wrote:
>> On Fri, Mar 03, 2023 at 08:13:37AM -0500, Stefan Hajnoczi wrote:
>> > On Thu, Mar 02, 2023 at 06:57:24PM -0500, Michael S. Tsirkin wrote:
>> > > On Thu, Mar 02, 2023 at 03:10:11PM -0500, Stefan Hajnoczi wrote:
>> > > > On Thu, Mar 02, 2023 at 08:05:02AM -0500, Michael S. Tsirkin wrote:
>> > > > > This introduces a general structure for group administration commands,
>> > > > > used to control device groups through their owner.
>> > > > > 
>> > > > > Following patches will introduce specific commands and an interface for
>> > > > > submitting these commands to the owner.
>> > > > > 
>> > > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
>> > > > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>> > > > > ---
>> > > > >  admin.tex        | 108 +++++++++++++++++++++++++++++++++++++++++++++++
>> > > > >  introduction.tex |   3 ++
>> > > > >  2 files changed, 111 insertions(+)
>> > > > > 
>> > > > > diff --git a/admin.tex b/admin.tex
>> > > > > index 3dc47be..7e28b77 100644
>> > > > > --- a/admin.tex
>> > > > > +++ b/admin.tex
>> > > > > @@ -46,4 +46,112 @@ \section{Device groups}\label{sec:Basic Facilities of a Virtio Device / Device g
>> > > > >  PCI transport (see \ref{sec:Virtio Transport Options / Virtio Over PCI Bus}).
>> > > > >  \end{description}
>> > > > >  
>> > > > > +\subsection{Group administration commands}\label{sec:Basic Facilities of a Virtio Device / Device groups / Group administration commands}
>> > > > >  
>> > > > > +The driver sends group administration commands to the owner device of
>> > > > 
>> > > > I notice that the terminology is simply "the driver". "Owner driver"
>> > > > and "group member driver" might be clearer because there will be two
>> > > > (possibly different) drivers involved.
>> > > 
>> > > Hmm I don't really want to repeat owner everywhere.
>> > > I will clarify that in this section simple "driver" and "device" are
>> > > owner, "member device" and "member driver" is always called explicitly.
>> > 
>> > Sounds good.
>> > 
>> > > > > +a group to control member devices of the group.
>> > > > > +This mechanism can
>> > > > > +be used, for example, to configure a member device before it is
>> > > > > +initialized by its driver.
>> > > > > +\footnote{The term "administration" is intended to be interpreted
>> > > > > +widely to include any kind of control. See specific commands
>> > > > > +for detail.}
>> > > > > +
>> > > > > +All the group administration commands are of the following form:
>> > > > > +
>> > > > > +\begin{lstlisting}
>> > > > > +struct virtio_admin_cmd {
>> > > > > +        /* Device-readable part */
>> > > > > +        le16 opcode;
>> > > > > +        /*
>> > > > > +         * 1 - SR-IOV
>> > > > > +         * 2 - 65535 reserved
>> > > > > +         */
>> > > > > +        le16 group_type;
>> > > > > +        /* unused, reserved for future extensions */
>> > > > > +        u8 reserved1[12];
>> > > > > +        le64 group_member_id;
>> > > > > +        u8 command_specific_data[];
>> > > > > +
>> > > > > +        /* Device-writable part */
>> > > > > +        le16 status;
>> > > > > +        le16 status_qualifier;
>> > > > > +        /* unused, reserved for future extensions */
>> > > > > +        u8 reserved2[4];
>> > > > > +        u8 command_specific_result[];
>> > > > > +};
>> > > > > +\end{lstlisting}
>> > > > > +
>> > > > > +For all commands, \field{opcode}, \field{group_type} and if
>> > > > > +necessary \field{group_member_id} and \field{command_specific_data} are
>> > > > > +set by the driver, and the owner device sets \field{status} and if
>> > > > > +needed \field{status_qualifier} and
>> > > > > +\field{command_specific_result}.
>> > > > > +
>> > > > > +Generally, any unused device-readable fields are set to zero by the driver
>> > > > > +and ignored by the device.  Any unused device-writeable fields are set to zero
>> > > > > +by the device and ignored by the driver.
>> > > > > +
>> > > > > +\field{opcode} specifies the command. The valid
>> > > > > +values for \field{opcode} can be found in the following table:
>> > > > > +
>> > > > > +\begin{tabular}{|l|l|}
>> > > > > +\hline
>> > > > > +opcode & Name & Command Description \\
>> > > > > +\hline \hline
>> > > > > +0x0000 - 0x7FFF & - &  Group administration commands    \\
>> > > > > +\hline
>> > > > > +0x8000 - 0xFFFF & - & Reserved    \\
>> > > > > +\hline
>> > > > > +\end{tabular}
>> > > > 
>> > > > I thought all commands are "group administration commands" but this
>> > > > table makes it look like they are just a subset (0x0000 - 0x7FFF) of
>> > > > group administration commands, which is a paradox.
>> > > 
>> > > Well the rest are reserved, maybe we will have more command types who
>> > > knows. No?
>> > 
>> > I see. Does that mean the reserved commands don't need to be in the same
>> > format as struct virtio_admin_cmd?
>> 
>> I am not good in predicting future ...
>> 
>> > The entire section is called "Group administration commands" but I get
>> > the impression it's talking both about admin virtqueue commands in
>> > general and specifically about group administration commands.
>> > 
>> > Is it possible to structure this as follows:
>> > 
>> >   Admin Commands
>> >     ...common stuff...
>> >     Group Administration Commands (0x0000-0x7fff)
>> >       ...specific to group administration commands...
>> >     Reserved (0x8000-0xffff)
>> 
>> What if I just write it like this:
>> 
>> 
>> > > > > +\hline \hline
>> > > > > +0x0000 - 0x7FFF & - &  commands using struct virtio_admin_cmd    \\
>> > > > > +\hline
>> > > > > +0x8000 - 0xFFFF & - & Reserved for future commands (possibly using a different structure)    \\
>> 
>> 
>> will this address the comment?
>
>Yes, thanks.

What is the reason for having this table? I fail to see it.


>
>Stefan