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

[Stefan Hajnoczi <stefanha@redhat.com>]

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.

> +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.

> +
> +The \field{group_type} specifies the group type identifier.
> +The \field{group_member_id} specifies the member identifier within the group.
> +See section \ref{sec:Introduction / Terminology / Device group}
> +for the definition of the group type identifier and group member
> +identifier.
> +
> +The following table describes possible \field{status} values;
> +to simplify common implementations, they are intentionally
> +matching common \hyperref[intro:errno]{Linux error names and numbers}:
> +
> +\begin{tabular}{|l|l|l|}
> +\hline
> +Status (decimal) & Name & Description \\
> +\hline \hline
> +00   & VIRTIO_ADMIN_STATUS_OK    & successful completion  \\
> +\hline
> +22   & VIRTIO_ADMIN_STATUS_EINVAL    & invalid command \\
> +\hline
> +other   & -    & group administration command error  \\
> +\hline
> +\end{tabular}
> +
> +When \field{status} is VIRTIO_ADMIN_STATUS_OK, \field{status_qialifier}

s/qialifier/qualifier/

> +is reserved and set to zero by the device.
> +
> +When \field{status} is VIRTIO_ADMIN_STATUS_EINVAL,
> +the following table describes possible \field{status_qialifier} values:

s/qialifier/qualifier/

> +\begin{tabular}{|l|l|l|}
> +\hline
> +Status & Name & Description \\
> +\hline \hline
> +0x00   & VIRTIO_ADMIN_STATUS_Q_INVALID_COMMAND   & command error: no additional information  \\
> +\hline
> +0x01   & VIRTIO_ADMIN_STATUS_Q_INVALID_OPCODE    & unsupported or invalid \field{opcode}  \\
> +\hline
> +0x02   & VIRTIO_ADMIN_STATUS_Q_INVALID_FIELD    & unsupported or invalid field within \field{command_specific_data}  \\
> +\hline
> +0x03   & VIRTIO_ADMIN_STATUS_Q_INVALID_GROUP    & unsupported or invalid \field{group_type} \\
> +\hline
> +0x04   & VIRTIO_ADMIN_STATUS_Q_INVALID_MEMBER    & unsupported or invalid \field{group_member_id} \\
> +\hline
> +0x05-0xFFFF   & -    & reserved for future use \\
> +\hline
> +\end{tabular}
> +
> +Each command uses a different \field{command_specific_data} and
> +\field{command_specific_result} structures and the length of
> +\field{command_specific_data} and \field{command_specific_result}
> +depends on these structures and is described separately or is
> +implicit in the structure description.

On more thing:

Does the owner device see commands in order but may complete them in any
order?

I think this information might be useful just to make it clear that
driver authors shouldn't make assumptions about ordering and completion
order, e.g. pipelining a bunch of dependent commands doesn't work
because the first command is not necessarily completed before the second
command is started.

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