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Subject: Re: [virtio-comment] [PATCH] virtio-dmabuf: Add specification details for this device
On 03.02.21 09:40, Vivek Kasireddy wrote:
> The virtio dmabuf device provides a way to share a page backed dmabuf
> created in the Guest with the Host. The actual sharing is accomplished
> by recreating the dmabuf on the Host using the page metadata shared by
> the guest.
What's the use case for this?
Jan
>
> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
> Signed-off-by: Dongwon Kim <dongwon.kim@intel.com>
> ---
> conformance.tex | 30 ++++++++++--
> content.tex | 3 ++
> virtio-vdmabuf.tex | 120 +++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 149 insertions(+), 4 deletions(-)
> create mode 100644 virtio-vdmabuf.tex
>
> diff --git a/conformance.tex b/conformance.tex
> index e78adfd..1f972ae 100644
> --- a/conformance.tex
> +++ b/conformance.tex
> @@ -28,8 +28,9 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
> \ref{sec:Conformance / Driver Conformance / RPMB Driver Conformance},
> \ref{sec:Conformance / Driver Conformance / IOMMU Driver Conformance},
> \ref{sec:Conformance / Driver Conformance / Sound Driver Conformance}
> -\ref{sec:Conformance / Driver Conformance / Memory Driver Conformance} or
> -\ref{sec:Conformance / Driver Conformance / I2C Adapter 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 / Dmabuf Driver Conformance}.
>
> \item Clause \ref{sec:Conformance / Legacy Interface: Transitional Device and Transitional Driver Conformance}.
> \end{itemize}
> @@ -50,8 +51,9 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
> \ref{sec:Conformance / Device Conformance / RPMB Device Conformance},
> \ref{sec:Conformance / Device Conformance / IOMMU Device Conformance},
> \ref{sec:Conformance / Device Conformance / Sound Device Conformance}
> -\ref{sec:Conformance / Device Conformance / Memory Device Conformance} or
> -\ref{sec:Conformance / Device Conformance / I2C Adapter Device Conformance}.
> +\ref{sec:Conformance / Device Conformance / Memory Device Conformance}
> +\ref{sec:Conformance / Device Conformance / I2C Adapter Device Conformance} or
> +\ref{sec:Conformance / Driver Conformance / Dmabuf Driver Conformance}.
>
> \item Clause \ref{sec:Conformance / Legacy Interface: Transitional Device and Transitional Driver Conformance}.
> \end{itemize}
> @@ -276,6 +278,16 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
> \item \ref{drivernormative:Device Types / I2C Adapter Device / Device Operation}
> \end{itemize}
>
> +\conformance{\subsection}{Dmabuf Driver Conformance}\label{sec:Conformance / Driver Conformance / Dmabuf Driver Conformance}
> +
> +A Dmabuf driver MUST conform to the following normative statements:
> +
> +\begin{itemize}
> +\item \ref{drivernormative:Device Types / Dmabuf Device / Device Operation / VM ID}
> +\item \ref{drivernormative:Device Types / Dmabuf Device / Device Operation / Export}
> +\item \ref{drivernormative:Device Types / Dmabuf Device / Device Operation / Release}
> +\end{itemize}
> +
> \conformance{\section}{Device Conformance}\label{sec:Conformance / Device Conformance}
>
> A device MUST conform to the following normative statements:
> @@ -503,6 +515,16 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
> \item \ref{devicenormative:Device Types / I2C Adapter Device / Device Operation}
> \end{itemize}
>
> +\conformance{\subsection}{Dmabuf Device Conformance}\label{sec:Conformance / Device Conformance / Dmabuf Device Conformance}
> +
> +A Dmabuf device MUST conform to the following normative statements:
> +
> +\begin{itemize}
> +\item \ref{drivernormative:Device Types / Dmabuf Device / Device Operation / VM ID}
> +\item \ref{drivernormative:Device Types / Dmabuf Device / Device Operation / Export}
> +\item \ref{drivernormative:Device Types / Dmabuf Device / Device Operation / Release}
> +\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 1ca24c1..b6ea383 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -2846,6 +2846,8 @@ \chapter{Device Types}\label{sec:Device Types}
> \hline
> 35 & Watchdog \\
> \hline
> +36 & Dmabuf device \\
> +\hline
> \end{tabular}
>
> Some of the devices above are unspecified by this document,
> @@ -6508,6 +6510,7 @@ \subsubsection{Legacy Interface: Framing Requirements}\label{sec:Device
> \input{virtio-sound.tex}
> \input{virtio-mem.tex}
> \input{virtio-i2c.tex}
> +\input{virtio-vdmabuf.tex}
>
> \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
>
> diff --git a/virtio-vdmabuf.tex b/virtio-vdmabuf.tex
> new file mode 100644
> index 0000000..18a4e2c
> --- /dev/null
> +++ b/virtio-vdmabuf.tex
> @@ -0,0 +1,120 @@
> +\section{Dmabuf Device}\label{sec:Device Types / Dmabuf Device}
> +
> +The virtio dmabuf device is a virtual dmabuf transfer device that provides
> +a way to share a page-backed dmabuf created in the Guest with the device.
> +Once shared, the driver and the device would use the same underlying memory
> +associated with the original dmabuf but not at the same time.
> +
> +\subsection{Device ID}\label{sec:Device Types / Dmabuf Device / Device ID}
> + 36
> +
> +\subsection{Virtqueues}\label{sec:Device Types / Dmabuf Device / Virtqueues}
> +\begin{description}
> +\item[0] recv
> +\item[1] send
> +\end{description}
> +
> +\subsection{Feature bits}\label{sec:Device Types / Dmabuf Device / Feature bits}
> +
> +No specific feature bits defined for this device.
> +
> +\subsection{Device configuration layout}\label{sec:Device Types / Dmabuf Device / Device configuration layout}
> +
> +No specific layout defined for this device.
> +
> +\subsection{Device Initialization}\label{sec:Device Types / Dmabuf Device / Device Initialization}
> +
> +\begin{enumerate}
> +\item Both the send and recv virtqueues are initialized to handle messages.
> +\end{enumerate}
> +
> +\subsection{Device Operation}\label{sec:Device Types / Dmabuf Device / Device Operation}
> +
> +Messages that are sent or received are of the following format:
> +
> +\begin{lstlisting}
> +struct virtio_vdmabuf_msg {
> + le32 cmd;
> + le32 op[64];
> +};
> +\end{lstlisting}
> +
> +The field \field{cmd} is initialized with one of the following:
> +
> +\begin{lstlisting}
> +enum virtio_vdmabuf_cmd {
> + VIRTIO_VDMABUF_CMD_NEED_VMID = 1,
> + VIRTIO_VDMABUF_CMD_EXPORT = 2,
> + VIRTIO_VDMABUF_CMD_DMABUF_REL =3,
> +};
> +\end{lstlisting}
> +
> +Based on the field \field{cmd}, the 256 bytes represented by the field
> +\field{op} are either zeroed out or contain metadata. They are zeroed out
> +if \field{cmd} is VIRTIO_VDMABUF_CMD_NEED_VMID. In other cases, the metadata
> +is formatted as below.
> +
> +The first 16 bytes contains a unique 128-bit Identifier of the following
> +format:
> +\begin{lstlisting}
> +struct virtio_vdmabuf_buf_id_t{
> + le64 id;
> + le32 rng_key[2];
> +};
> +\end{lstlisting}
> +
> +The first 4 bytes of \field{id} contain an ID associated with the device and
> +the other 4 bytes contain a counter. The last 8 bytes of the above structure
> +represented by \field{rng_key} contain random data to ensure that the 128-bit
> +identifier is indeed unique at any given time.
> +
> +The remaining 240 bytes contain private data shared between the driver and
> +the device.
> +
> +\subsubsection{Virtqueue Flow Control}\label{sec:Device Types / Dmabuf Device / Device Operation / Virtqueue Flow Control}
> +
> +The send virtqueue carries messages initiated by an application running in the
> +Guest and responses to previously sent messages. The recv virtqueue carries
> +messages initiated by the device.
> +
> +\subsubsection{VM ID}\label{sec:Device Types / Dmabuf Device / Device Operation / VM ID}
> +
> +The driver sends a VM ID message to the device via the send virtqueue
> +after setting the \field{cmd} to VIRTIO_VDMABUF_CMD_NEED_VMID.
> +
> +In response, the device would queue up a message on the recv virtqueue with
> +the \field{cmd} set to VIRTIO_VDMABUF_CMD_NEED_VMID and the first 4 bytes of
> +\field{op} containing the ID associated with the device.
> +
> +\drivernormative{\paragraph}{Device Operation: VM ID}{Device Types / Dmabuf Device / Device Operation / VM ID}
> +
> +The rest of the message MUST be zeroed out.
> +
> +\subsubsection{Export}\label{sec:Device Types / Dmabuf Device / Device Operation / Export}
> +
> +The driver sends an Export message to the device via the send virtqueue
> +after populating the message as follows:
> +
> +\drivernormative{\paragraph}{Device Operation: Export}{Device Types / Dmabuf Device / Device Operation / Export}
> +
> +The driver MUST set \field{cmd} to VIRTIO_VDMABUF_CMD_EXPORT.
> +
> +The driver MUST set the first 16 bytes of \field{op} to a new unique ID.
> +
> +The driver MUST populate the next 20 bytes of \field{op} with valid meta data
> +associated with the buffer represented by the ID.
> +
> +\subsubsection{Release}\label{sec:Device Types / Dmabuf Device / Device Operation / Release}
> +
> +The device sends a Release message to the driver via the recv virtqueue
> +after populating the message as follows:
> +
> +\drivernormative{\paragraph}{Device Operation: Release}{Device Types / Dmabuf Device / Device Operation / Release}
> +
> +The device MUST set \field{cmd} to VIRTIO_VDMABUF_CMD_RELEASE.
> +
> +The device MUST set the first 16 bytes of \field{op} to a valid unique ID
> +that was previously shared by the driver.
> +
> +The device must zero out the remaining part of the message.
> +
>
--
Siemens AG, T RDA IOT
Corporate Competence Center Embedded Linux
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