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Subject: Re: [PATCH v4] Add virtio parameter server device specification
On Thu, Jun 10, 2021 at 4:19 PM Hao Chen <chenhaosjtuacm@google.com> wrote:
>
> This patch introduces a new type of device: parameter server. The device
> acts as a key-value store and the driver can read from, write to or
> subscribe to the properties in the server.
>
> Signed-off-by: Hao Chen <chenhaosjtuacm@google.com>
> ---
> conformance.tex | 26 +++++-
> content.tex | 1 +
> virtio-ps.tex | 216 ++++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 239 insertions(+), 4 deletions(-)
> create mode 100644 virtio-ps.tex
>
> diff --git a/conformance.tex b/conformance.tex
> index a164cbb..0d6b1a5 100644
> --- a/conformance.tex
> +++ b/conformance.tex
> @@ -29,8 +29,9 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
> \ref{sec:Conformance / Driver Conformance / IOMMU Driver Conformance},
> \ref{sec:Conformance / Driver Conformance / Sound Driver Conformance},
> \ref{sec:Conformance / Driver Conformance / Memory Driver Conformance},
> -\ref{sec:Conformance / Driver Conformance / I2C Adapter Driver Conformance} or
> -\ref{sec:Conformance / Driver Conformance / SCMI Driver Conformance}.
> +\ref{sec:Conformance / Driver Conformance / I2C Adapter Driver Conformance},
> +\ref{sec:Conformance / Driver Conformance / SCMI Driver Conformance} or
> +\ref{sec:Conformance / Driver Conformance / Parameter Server Driver Conformance}.
>
> \item Clause \ref{sec:Conformance / Legacy Interface: Transitional Device and Transitional Driver Conformance}.
> \end{itemize}
> @@ -52,8 +53,9 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
> \ref{sec:Conformance / Device Conformance / IOMMU Device Conformance},
> \ref{sec:Conformance / Device Conformance / Sound Device Conformance},
> \ref{sec:Conformance / Device Conformance / Memory Device Conformance},
> -\ref{sec:Conformance / Device Conformance / I2C Adapter Device Conformance} or
> -\ref{sec:Conformance / Device Conformance / SCMI Device Conformance}.
> +\ref{sec:Conformance / Device Conformance / I2C Adapter Device Conformance},
> +\ref{sec:Conformance / Device Conformance / SCMI Device Conformance}or
> +\ref{sec:Conformance / Device Conformance / Parameter Server Device Conformance}.
>
> \item Clause \ref{sec:Conformance / Legacy Interface: Transitional Device and Transitional Driver Conformance}.
> \end{itemize}
> @@ -288,6 +290,14 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
> \item \ref{drivernormative:Device Types / SCMI Device / Device Operation / Setting Up eventq Buffers}
> \end{itemize}
>
> +\conformance{\subsection}{Parameter Server Driver Conformance}\label{sec:Conformance / Driver Conformance / Parameter Server Driver Conformance}
> +
> +A parameter server driver MUST conform to the following normative statements:
> +
> +\begin{itemize}
> +\item \ref{drivernormative:Device Types / Parameter Server / Device Operation}
> +\end{itemize}
> +
> \conformance{\section}{Device Conformance}\label{sec:Conformance / Device Conformance}
>
> A device MUST conform to the following normative statements:
> @@ -527,6 +537,14 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
> \item \ref{devicenormative:Device Types / SCMI Device / Device Operation / Shared Memory Operation}
> \end{itemize}
>
> +\conformance{\subsection}{Parameter Server Device Conformance}\label{sec:Conformance / Device Conformance / Parameter Server Device Conformance}
> +
> +A parameter server device MUST conform to the following normative statements:
> +
> +\begin{itemize}
> +\item \ref{devicenormative:Device Types / Parameter Server / Device Operation}
> +\end{itemize}
> +
> \conformance{\section}{Legacy Interface: Transitional Device and Transitional Driver Conformance}\label{sec:Conformance / Legacy Interface: Transitional Device and Transitional Driver Conformance}
> A conformant implementation MUST be either transitional or
> non-transitional, see \ref{intro:Legacy
> diff --git a/content.tex b/content.tex
> index 9232d5c..b980a93 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -6568,6 +6568,7 @@ \subsubsection{Legacy Interface: Framing Requirements}\label{sec:Device
> \input{virtio-mem.tex}
> \input{virtio-i2c.tex}
> \input{virtio-scmi.tex}
> +\input{virtio-ps.tex}
>
> \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
>
> diff --git a/virtio-ps.tex b/virtio-ps.tex
> new file mode 100644
> index 0000000..2a226c4
> --- /dev/null
> +++ b/virtio-ps.tex
> @@ -0,0 +1,216 @@
> +\section{Parameter Server}\label{sec:Device Types / Parameter Server}
> +
> +The parameter server device manages a set of values with unique property IDs. These values may
> +either be static (i.e. have a constant value) or be dynamic (i.e. value may change over time).
> +The driver can get and set values, get value configurations, subscribe and unsubscribe dynamic
> +properties from the device. The driver will get updates when subscribed value changes. The device
> +processes the requests from the driver, enforces the value access rules, and may potentially alter
> +the behavior of external systems as a result of driver operations.
> +
> +\subsection{Device ID}\label{sec:Device Types / Parameter Server / Device ID}
> +
> +38
> +
> +\subsection{Virtqueues}\label{sec:Device Types / Parameter Server / Virtqueues}
> +
> +\begin{description}
> +\item[0] cmdq
> +\item[1] eventq
> +\end{description}
> +
> +\subsection{Feature Bits}\label{sec:Device Types / Parameter Server / Feature Bits}
> +
> +None currently defined.
> +
> +\subsection{Device Configuration Layout}\label{sec:Device Types / Parameter Server / Device Configuration Layout}
> +
> +\begin{lstlisting}
> +struct virtio_parameter_server_config {
> + char name[128];
> +};
> +\end{lstlisting}
> +
> +A device configuration space only contains the name of the device, which can be used by the
> +userspace for identification. \field{name} is a zero-terminated char string. The maximum length
> +of \field{name} is 127.
> +
> +\subsection{Device Initialization}
> +
> +\begin{enumerate}
> +\item The virtqueues are initialized.
> +\end{enumerate}
> +
> +\subsection{Device Operation}\label{sec:Device Types / Parameter Server / Device Operation}
> +
> +The driver puts requests to read, write, subscribe to, or unsubscribe from, parameters onto the
> +cmdq virtqueue. The device also puts its responses to the driver's requests onto the cmdq
> +virtqueue. The device puts any updates to values that the driver has subscribed to onto the
> +eventq virtqueue. The
> +\field{prop_id}, \field{prop_item_id} pair is the primary key for the values stored in the
> +parameter server, while the values with the same \field{prop_id} share the same configuration.
> +For example, \field{prop_id} 12 with \field{prop_item_id} 0, 1 and 2 represent 3 different values
> +sharing the same \field{virtio_parameter_server_config}. \field{prop_id} is also used for
> +subscriptions, meaning that if you subscribe on a prop_id, you will receive every updates on that
> +prop_id regardless of what prop_item_id it contains. \field{prop_item_id} is not used in
> +subscription.
> +
> +The layout of requests and responses are defined below:
> +
> +\begin{lstlisting}
> +struct virtio_parameter_server_request {
> + le64 timestamp;
> + le32 prop_id;
> + le32 prop_item_id;
> + u8 op;
> + u8 payload[<actual payload size>];
> +};
> +
> +struct virtio_parameter_server_response {
> + le64 timestamp;
> + le32 prop_id;
> + le32 prop_item_id;
> + u16 op;
> + u16 ret_value;
> + u8 payload[<actual payload size>];
> +};
> +
> +/* Reserved prop_id and prop_item_id */
> +#define VIRTIO_PARAMETER_SERVER_OP_ALL_PROP INT_MAX
> +
> +/* Supported operations */
> +#define VIRTIO_PARAMETER_SERVER_OP_INVALID 0
> +#define VIRTIO_PARAMETER_SERVER_OP_GET_PROP_CONFIG 1
> +#define VIRTIO_PARAMETER_SERVER_OP_GET_PROP_VALUE 2
> +#define VIRTIO_PARAMETER_SERVER_OP_SET_PROP_VALUE 3
> +#define VIRTIO_PARAMETER_SERVER_OP_SUBSCRIBE_PROP 4
> +#define VIRTIO_PARAMETER_SERVER_OP_UNSUBSCRIBE_PROP 5
> +\end{lstlisting}
> +
> +The layout of messages in eventq is defined below:
> +
> +\begin{lstlisting}
> +struct virtio_parameter_server_event_msg {
> + le64 timestamp;
> + le32 prop_id;
> + le32 prop_item_id;
> + u8 payload[<actual payload size>];
> +};
> +\end{lstlisting}
> +
> +There will be exactly one response for each request in the cmdq, even if \field{op} is invalid. For some operations,
> +the \field{payload} of requests and/or responses may be empty. The content of the payload depend on the operation.
> +
> +\subsubsection{Property Configuration Layout}\label{sec:Device Types / Parameter Server / Device Operation / Property Configuration Layout}
> +
> +\begin{lstlisting}
> +// The max size of virtio_parameter_server_config, including
> +// fixed-length members and params
> +#define VIRTIO_PARAMETER_SERVER_CONFIG_MAX_SIZE_BYTE 4096
> +
> +struct virtio_parameter_server_prop_config {
> + le32 prop_id;
> + le32 mode;
> + le32 min_sample_freq;
> + le32 max_sample_freq;
> + le32 encoding[5];
> + le32 param_size;
> + char desc[256];
> + u8 params[<actual param size>];
> +};
> +\end{lstlisting}
> +
> +while \field{mode} is the bitwise-or-combination of the following:
> +
> +\begin{lstlisting}
> +enum virtio_parameter_server_prop_mode {
> + /* access */
> + VIRTIO_PARAMETER_SERVER_M_READ = 0x1,
> + VIRTIO_PARAMETER_SERVER_M_WRITE = 0x2,
> + VIRTIO_PARAMETER_SERVER_M_READ_WRITE = 0x3,
> +
> + /* change */
> + VIRTIO_PARAMETER_SERVER_M_STATIC = 0x4,
> + VIRTIO_PARAMETER_SERVER_M_MUTABLE = 0x8,
> + VIRTIO_PARAMETER_SERVER_M_CONTINUOUS = 0xc,
> +};
> +\end{lstlisting}
> +
> +Both VIRTIO_PARAMETER_SERVER_M_MUTABLE and VIRTIO_PARAMETER_SERVER_M_CONTINUOUS are dynamic
> +properties. A VIRTIO_PARAMETER_SERVER_M_MUTABLE value will change due to the set value operation
> +from the driver, or actions of the external system; a VIRTIO_PARAMETER_SERVER_M_CONTINUOUS value
> +is expected to be generated by means of a sensor updating at a steady frequency.
> +
> +The reason we want to handle "MUTABLE" and "CONTNUOUS" differently is, the MUTABLE values are not
> +constantly changing, so the device may be able to send every updates of it to the driver; while
> +CONTINUOUS values are changing frequently (e.g., sensor outputs) and the device should decide how
> +to sample it and provide a sample rate range (\field{min_sample_freq} and \field{max_sample_freq})
> +
> +The properties with the same \field{prop_id} share the configuration. \field{min_sample_freq} and
> +\field{max_sample_freq} are the sampling rate range for the
> +\field{VIRTIO_PARAMETER_SERVER_M_CONTINUOUS} values. \field{desc} is the optional zero-terminated
> +char string description. \field{params} are for the customized configuration parameters.
> +
> +The integer array \field{encoding} specifies the number of different primitive value in the
> +property value.
> +
> +\begin{lstlisting}
> +#define VIRTIO_PARAMETER_SERVER_ENCODING_INDEX_NUM_INT64 0
> +#define VIRTIO_PARAMETER_SERVER_ENCODING_INDEX_NUM_FLOAT64 1
> +#define VIRTIO_PARAMETER_SERVER_ENCODING_INDEX_NUM_INT32 2
> +#define VIRTIO_PARAMETER_SERVER_ENCODING_INDEX_NUM_BYTE 3
> +#define VIRTIO_PARAMETER_SERVER_ENCODING_INDEX_HAS_STRING 4
> +\end{lstlisting}
> +
> +If the driver asks for ALL property configurations by setting the \field{prop_id} of the request to
> +VIRTIO_PARAMETER_SERVER_OP_ALL_PROP, then the \field{payload} of virtio_parameter_server_response
> +will be multiple property configurations, serialized 1-by-1.
> +
> +\subsubsection{Property Value Layout}\label{sec:Device Types / Parameter Server / Device Operation / Property Value Layout}
> +
> +The property value payload begins with 5 arrays. The order is the same as the \field{encoding} array defined above.
> +For each array, it begins with a 32-bit integer for length (number of elements). Empty array will be a 32-bit 0, while
> +-1 means the array does not exist. The elements follows the length, and the size of the encoded array will be padded
> +to 4 bytes. String is encoded as a zero-terminated char array,
> +\field{encoding[VIRTIO_PARAMETER_SERVER_ENCODING_INDEX_HAS_STRING]} indicates the existence of the string.
> +
> +After the arrays, there may be customized data, which is encoded as a byte array.
> +
> +For example, if \field{encoding} of virtio_parameter_server_prop_config of property A is \field{[2, 0, 0, 0, 1]},
> +then property A contains two 64-bit integers and a string. The encoded value consists of the following (from top to bottom):
> +
> +\begin{lstlisting}
> +2 (32-bit, meaning 2 64-bit integers)
> +64-bit integer
> +64-bit integer
> +-1 (32-bit, meaning no 64-bit float number array)
> +-1 (32-bit, meaning no 32-bit integer array)
> +-1 (32-bit, meaning no byte array)
> +14 (32-bit integer, length of the char string, including trailing zero, excluding padding zeros)
> +"sample string\0"
> +padding zeros to 4 bytes. In this case there will be 2 zero bytes.
> +(optional) byte array length + data if there are customized data
> +\end{lstlisting}
> +
> +\drivernormative{\subsubsection}{Device Operation}{Device Types / Parameter Server / Device Operation}
> +
> +The driver MUST NOT send undefined ops.
> +
> +The driver MUST NOT put descriptors into the eventq.
> +
> +The payload size of requests MUST be padded to 4 bytes.
> +
> +\devicenormative{\subsubsection}{Device Operation}{Device Types / Parameter Server / Device Operation}
> +
> +\field{name} of the device configuration MUST be non-empty.
> +
> +The unused bits of the message header MUST be 0.
> +
> +The \field{prop_item_id} of VIRTIO_PARAMETER_SERVER_OP_GET_PROP_CONFIG,
> +VIRTIO_PARAMETER_SERVER_OP_SUBSCRIBE_PROP and VIRTIO_PARAMETER_SERVER_OP_UNSUBSCRIBE_PROP requests
> +MUST be ignored.
> +
> +The device MUST send exact 1 response for every received request.
> +
> +The payload size of responses and event messages MUST be padded to 4 bytes.
> +
> +The param size of property configurations MUST be padded to 4 bytes.
> --
> 2.32.0.272.g935e593368-goog
>
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