[PATCH 0/1] virtio-media: Add device specification

[PATCH 0/1] virtio-media: Add device specification

[Albert Esteve]

Hi,

This a formal attempt of including virtio-media
device specification.

Virtio-media came from a discussion on virtio-dev
mailing list, which lead to presenting virtio-v4l2[1]
specification as an alternative to virtio-video.

Later, virtio-v4l2 was renamed to virtio-media[2]
and published through:

https://github.com/chromeos/virtio-media

The repository above includes a guest V4L2 driver able
to pass v4l2-compliance when proxying the vivid/vicodec
virtual devices or an actual UVC camera using the
crosvm V4L2 proxy device. Steps to reproduce are
also detailed[3].

There is some overlap with virtio-video in regards
to which devices it can handle. However,
as virtio-media will likely be the virtualization
solution for ChromeOS (already landed into the chromeos
organization) and possibly other Google projects for
media devices, it would be desirable to include the
specification in the next virtio release despite
the aforementioned overlap.

The device ID in this document differs from
the ID in the virtio-media project repository.
And it will probably need some discussion on which
would be the correct definitive ID.

Full PDF: https://drive.google.com/file/d/1PG1YxzbSvQHPphFhbUKyKKdvuwO6shyi/view?usp=sharing
PDF with the media section only: https://drive.google.com/file/d/1Y7kAGzlUfl30VIUx9wQtz5sFTkWnBiyA/view?usp=sharing

[1] https://mail.google.com/mail/u/0?ui=2&ik=73ebd65ebd&attid=0.1&permmsgid=msg-f:1767388565327924962&th=1887068940754ee2&view=att&disp=inline&realattid=f_libalimc0
[2] https://www.mail-archive.com/virtio-dev@lists.oasis-open.org/msg12665.html
[3] https://github.com/chromeos/virtio-media/blob/main/TRY_IT_OUT.md

Albert Esteve (1):
  virtio-media: Add virtio media device specification

 conformance.tex                           |  13 +-
 content.tex                               |   1 +
 device-types/media/description.tex        | 574 ++++++++++++++++++++++
 device-types/media/device-conformance.tex |  11 +
 device-types/media/driver-conformance.tex |   9 +
 5 files changed, 604 insertions(+), 4 deletions(-)
 create mode 100644 device-types/media/description.tex
 create mode 100644 device-types/media/device-conformance.tex
 create mode 100644 device-types/media/driver-conformance.tex

-- 
2.44.0

[PATCH 1/1] virtio-media: Add virtio media device specification

[Albert Esteve]

Virtio-media is an encapsulation of the V4L2 UAPI into
virtio, able to virtualize any video device supported
by V4L2

Note that virtio-media does not require the use of a
V4L2 device driver or of Linux on the host or
guest side - V4L2 is only used as a host-guest protocol,
and both sides are free to convert it from/to any
model that they wish to use.

Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
 conformance.tex                           |  13 +-
 content.tex                               |   1 +
 device-types/media/description.tex        | 574 ++++++++++++++++++++++
 device-types/media/device-conformance.tex |  11 +
 device-types/media/driver-conformance.tex |   9 +
 5 files changed, 604 insertions(+), 4 deletions(-)
 create mode 100644 device-types/media/description.tex
 create mode 100644 device-types/media/device-conformance.tex
 create mode 100644 device-types/media/driver-conformance.tex

diff --git a/conformance.tex b/conformance.tex
index dc00e84..c369da1 100644
--- a/conformance.tex
+++ b/conformance.tex
@@ -32,8 +32,10 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
 \ref{sec:Conformance / Driver Conformance / Memory Driver Conformance},
 \ref{sec:Conformance / Driver Conformance / I2C Adapter Driver Conformance},
 \ref{sec:Conformance / Driver Conformance / SCMI Driver Conformance},
-\ref{sec:Conformance / Driver Conformance / GPIO Driver Conformance} or
-\ref{sec:Conformance / Driver Conformance / PMEM Driver Conformance}.
+\ref{sec:Conformance / Driver Conformance / GPIO Driver Conformance},
+\ref{sec:Conformance / Driver Conformance / PMEM Driver Conformance} or
+\ref{sec:Conformance / Driver Conformance / Media Driver Conformance}.
+
 
     \item Clause \ref{sec:Conformance / Legacy Interface: Transitional Device and Transitional Driver Conformance}.
   \end{itemize}
@@ -59,8 +61,9 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
 \ref{sec:Conformance / Device Conformance / Memory Device Conformance},
 \ref{sec:Conformance / Device Conformance / I2C Adapter Device Conformance},
 \ref{sec:Conformance / Device Conformance / SCMI Device Conformance},
-\ref{sec:Conformance / Device Conformance / GPIO Device Conformance} or
-\ref{sec:Conformance / Device Conformance / PMEM Device Conformance}.
+\ref{sec:Conformance / Device Conformance / GPIO Device Conformance},
+\ref{sec:Conformance / Device Conformance / PMEM Device Conformance} or
+\ref{sec:Conformance / Device Conformance / Media Device Conformance}.
 
     \item Clause \ref{sec:Conformance / Legacy Interface: Transitional Device and Transitional Driver Conformance}.
   \end{itemize}
@@ -152,6 +155,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
 \input{device-types/scmi/driver-conformance.tex}
 \input{device-types/gpio/driver-conformance.tex}
 \input{device-types/pmem/driver-conformance.tex}
+\input{device-types/media/driver-conformance.tex}
 
 \conformance{\section}{Device Conformance}\label{sec:Conformance / Device Conformance}
 
@@ -238,6 +242,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
 \input{device-types/scmi/device-conformance.tex}
 \input{device-types/gpio/device-conformance.tex}
 \input{device-types/pmem/device-conformance.tex}
+\input{device-types/media/device-conformance.tex}
 
 \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
diff --git a/content.tex b/content.tex
index 0a62dce..59925ae 100644
--- a/content.tex
+++ b/content.tex
@@ -767,6 +767,7 @@ \chapter{Device Types}\label{sec:Device Types}
 \input{device-types/scmi/description.tex}
 \input{device-types/gpio/description.tex}
 \input{device-types/pmem/description.tex}
+\input{device-types/media/description.tex}
 
 \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
 
diff --git a/device-types/media/description.tex b/device-types/media/description.tex
new file mode 100644
index 0000000..d67cc96
--- /dev/null
+++ b/device-types/media/description.tex
@@ -0,0 +1,574 @@
+\section{Media Device}\label{sec:Device Types / Media Device}
+
+The virtio media device follow the same model (and structures) as V4L2. It
+can be used to virtualize cameras, codec devices, or any other device
+supported by V4L2. The complete definition of V4L2 structures and ioctls can
+be found under the
+\href{https://www.kernel.org/doc/html/latest/userspace-api/media/index.html}{V4L2 UAPI documentation}.
+
+V4L2 is a UAPI that allows a less privileged entity (user-space) to use video
+hardware exposed by a more privileged entity (the kernel). Virtio-media is an
+encapsulation of this API into virtio, turning it into a virtualization API
+for all classes of video devices supported by V4L2, where the host plays the
+role of the kernel and the guest the role of user-space.
+
+The host is therefore responsible for presenting a virtual device that behaves
+like an actual V4L2 device, which the guest can control.
+
+Note that virtio-media does not require the use of a V4L2 device driver or of
+Linux on the host or guest side - V4L2 is only used as a host-guest protocol,
+and both sides are free to convert it from/to any model that they wish to use.
+
+This section relies on definitions from
+\href{https://www.kernel.org/doc/html/latest/userspace-api/media/index.html}{V4L2 UAPI documentation}.
+
+\subsection{Device ID}\label{sec:Device Types / Media Device / Device ID}
+
+42
+
+\subsection{Virtqueues}\label{sec:Device Types / Media Device / Virtqueues}
+
+\begin{description}
+\item[0] commandq - used for driver commands and device responses to these
+commands.
+\item[1] eventq - used for events sent by the device to the driver.
+\end{description}
+
+\devicenormative{\subsubsection}{Virtqueues}{Device Types / Media Device / Virtqueues}
+
+The device MUST return the descriptor chains it receives on the commandq as
+soon as possible, and must never hold them for indefinite periods of time.
+
+\drivernormative{\subsubsection}{Virtqueues}{Device Types / Media Device / Virtqueues}
+
+The driver MUST re-queue the descriptor chains returned by the device on the
+eventq as soon as possible, and must never hold them for indefinite periods
+of time.
+
+\subsection{Feature Bits}\label{sec:Device Types / Media Device / Feature Bits}
+
+None
+
+\subsection{Device Configuration Layout}\label{sec:Device Types / Media Device / Device Configuration Layout}
+
+The video device configuration space uses the following layout:
+
+\begin{lstlisting}
+struct virtio_media_config {
+    le32 device_caps;
+    le32 device_type;
+    u8 card[32];
+};
+\end{lstlisting}
+
+\begin{description}
+\item[\field{device_caps}] (driver-read-only) flags representing the device
+capabilities as used in
+\href{https://www.kernel.org/doc/html/v4.9/media/uapi/v4l/vidioc-querycap.html#c.v4l2_capability}{struct v4l2_capabilities}.
+Corresponds with the \field{device_caps} field in the \textit{struct video_device}.
+\item[\field{device_type}] (driver-read-only) informs the driver of the type
+of the video device. Corresponds with the \field{vfl_devnode_type} field of the device.
+\item[\field{card}] (driver-read-only) name of the device, a NUL-terminated
+UTF-8 string. Corresponds with the \field{card} field of the \textit{struct v4l2_capability}.
+If all the characters of the field are used, it does not need to be NUL-terminated.
+\end{description}
+
+\subsection{Device Initialization}
+
+\begin{enumerate}
+\item The driver reads the \field{device_caps} and \field{device_type} fields
+from the configuration layout to identify the device.
+\item The driver sets up the \field{commandq} and \field{eventq}.
+\item The driver may open a session to use the device and send V4L2 ioctls in
+order to receive more information about the device, such as supported
+formats or controls.
+\end{enumerate}
+
+\subsection{Device Operation}\label{sec:Device Types / Media Device / Device Operation}
+
+Commands are queued on the command queue by the driver for the device to
+process. The errors returned by each command are standard
+\href{https://www.kernel.org/doc/html/latest/userspace-api/media/gen-errors.html}{Linux kernel error codes}.
+For instance, a command that contains invalid options will return \textit{EINVAL}.
+
+Events are sent on the event queue by the device for the driver to handle.
+
+\subsubsection{Command Virtqueue}
+
+\paragraph{Device Operation: Command headers}
+
+\begin{lstlisting}
+#define VIRTIO_MEDIA_CMD_OPEN 1
+#define VIRTIO_MEDIA_CMD_CLOSE 2
+#define VIRTIO_MEDIA_CMD_IOCTL 3
+#define VIRTIO_MEDIA_CMD_MMAP 4
+#define VIRTIO_MEDIA_CMD_MUNMAP 5
+
+/* Header for all virtio commands from the driver to the device on the commandq. */
+struct virtio_media_cmd_header {
+	u32 cmd;
+	u32 __padding;
+};
+
+/* Header for all virtio responses from the device to the driver on the commandq. */
+struct virtio_media_resp_header {
+	u32 status;
+	u32 __padding;
+};
+\end{lstlisting}
+
+A command consists of a command header \textit{virtio_media_cmd_header}
+containing the following device-readable field:
+
+\begin{description}
+\item[\field{cmd}] specifies a device request type (VIRTIO_MEDIA_CMD_*).
+\end{description}
+
+A response consists of a response header \textit{virtio_media_resp_header}
+containing the following device-writable field:
+
+\begin{description}
+\item[\field{status}] indicates a device request status.
+\end{description}
+
+The status field can take 0 if the command was successful, or one of the
+standard Linux error codes if it was not.
+
+\drivernormative{\paragraph}{Device Operation: Command Virtqueue: Sessions}{Device Types / Media Device / Device Operation / Command Virtqueue}
+
+Sessions are how the device is multiplexed, allowing several distinct works to
+take place simultaneously. The driver needs to open a session before it can
+perform any useful operation on the device.
+
+\paragraph{Device Operation: Open device}
+
+\textbf{VIRTIO_MEDIA_CMD_OPEN} Command for creating a new session.
+
+This is the equivalent of calling \textit{open} on a V4L2 device node.
+The driver uses \textit{virtio_media_cmd_open} to send an open request.
+
+\begin{lstlisting}
+struct virtio_media_cmd_open {
+    struct virtio_media_cmd_header hdr;
+};
+\end{lstlisting}
+
+The device responds to \textit{VIRTIO_MEDIA_CMD_OPEN} with \textit{virtio_media_resp_open}.
+
+\begin{lstlisting}
+struct virtio_media_resp_open {
+    struct virtio_media_resp_header hdr;
+    u32 session_id;
+    u32 __padding;
+};
+\end{lstlisting}
+
+\begin{description}
+\item[\field{session_id}] specifies an identifier for the current session. The
+identifier can be used to perform other commands on the session, notably ioctls.
+\end{description}
+
+\devicenormative{\subparagraph}{Device Operation: Open device}{Device Types / Media Device / Device Operation / Open device}
+
+Upon success, the device MUST set a \field{session_id} in \textit{virtio_media_resp_open}
+to an integer that is NOT used by any other open session.
+
+\paragraph{Device Operation: Close device}
+
+\textbf{VIRTIO_MEDIA_CMD_CLOSE} Command for closing an active session.
+
+This is the equivalent of calling \textit{close} on a previously opened V4L2
+device node. All resources associated with this session will be freed.
+
+This command does not require a response from the device.
+
+\begin{lstlisting}
+struct virtio_media_cmd_close {
+    struct virtio_media_cmd_header hdr;
+    u32 session_id;
+    u32 __padding;
+};
+\end{lstlisting}
+
+\begin{description}
+\item[\field{session_id}] specifies an identifier for the session to close.
+\end{description}
+
+\drivernormative{\subparagraph}{Device Operation: Close device}{Device Types / Media Device / Device Operation / Close device}
+
+The session ID SHALL NOT be used again after queueing this command.
+
+\paragraph{Device Operation: V4L2 ioctls}
+
+\textbf{VIRTIO_MEDIA_CMD_IOCTL} Command for executing an ioctl on an open
+session.
+
+This command asks the device to run one of the `VIDIOC_*` ioctls on the active
+session.
+
+\begin{lstlisting}
+struct virtio_media_cmd_ioctl {
+    struct virtio_media_cmd_header hdr;
+    u32 session_id;
+    u32 code;
+    /* Followed by the relevant ioctl payload as defined in the macro */
+};
+\end{lstlisting}
+
+\begin{description}
+\item[\field{session_id}] specifies an identifier of thesession to run the ioctl on.
+\item[\field{code}] specifies the code of the \field{VIDIOC_*} ioctl to run.
+\end{description}
+
+The code is extracted from the
+\href{https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/videodev.html}{videodev2.h},
+header file. The file defines the ioctl's codes, type of payload, and
+direction. The code consists of the second argument of the \field{_IO*} macro.
+
+For example, the \textit{VIDIOC_G_FMT} is defined as follows:
+
+\begin{lstlisting}
+#define VIDIOC_G_FMT _IOWR('V',  4, struct v4l2_format)
+\end{lstlisting}
+
+This means that its ioctl code is \textit{4}, that its payload is a
+\textit{struct v4l2_format}, and that its direction is \textit{WR} (i.e., the
+payload is written by both the driver and the device).
+See Section \ref{sec:Device Types / Media Device / V4L2 ioctls / Ioctls payload}
+for more information about the direction of ioctls.
+
+The payload layout is always a 64-bit representation of the corresponding
+V4L2 structure, irrespective of the host and guest architecture.
+
+The device responds to \textit{VIRTIO_MEDIA_CMD_IOCTL} with \textit{virtio_media_resp_ioctl}.
+
+\begin{lstlisting}
+struct virtio_media_resp_ioctl {
+    struct virtio_media_resp_header hdr;
+    /* Followed by the ioctl payload as defined in the macro */
+};
+\end{lstlisting}
+
+\subparagraph{Ioctls payload}\label{sec:Device Types / Media Device / V4L2 ioctls / Ioctls payload}
+
+Each ioctl has a payload, which is defined by the third argument of the
+\field{_IO*} macro defining it. 
+
+The payload of an ioctl in the descriptor chain follows the command structure,
+the reponse structure, or both depending on the direction:
+
+\begin{itemize}
+\item \textbf{_IOR} is read-only for the driver, meaning the payload
+follows the response in the device-writable section of the descriptor chain.
+\item \textbf{_IOW} is read-only for the device, meaning the payload
+follows the command in the driver-writable section of the descriptor chain.
+\item \textbf{_IOWR} is writable by both the device and driver,
+meaning the payload must follow both the command in the driver-writable section
+of the descriptor chain, and the response in the device-writable section.
+\end{itemize}
+
+A common optimization for \textit{WR} ioctls is to provide the payload using
+descriptors that both point to the same buffer. This mimics the behavior of
+V4L2 ioctls where the data is only passed once and used as both input and
+output by the kernel.
+
+\devicenormative{\subparagraph}{Device Operation: V4L2 ioctls}{Device Types / Media Device / Device Operation / V4L2 ioctls}
+
+In case of success of a device-writable ioctl, the device MUST always write the
+payload in the device-writable part of the descriptor chain.
+
+In case of failure of a device-writable ioctl, the device is free to write the
+payload in the device-writable part of the descriptor chain or not. Some errors
+may still result in the payload being updated, and in this case the device is
+expected to write the updated payload. If the device has not written the
+payload after an error, the driver MUST assume that the payload has not been
+modified.
+
+\subparagraph{Handling of pointers in ioctl payload}
+
+A few structures used as ioctl payloads contain pointers to further
+data needed for the ioctl. There are notably:
+
+\begin{itemize}
+\item The \field{planes} pointer of
+\href{https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/buffer.html#struct-v4l2-buffer}{struct v4l2_buffer},
+which size is determined by the length member.
+\item The \field{controls} pointer of \textit{struct v4l2_ext_controls}, which
+size is determined by the count member.
+\end{itemize}
+
+If the size of the pointed area is determined to be non-zero, then the main
+payload is immediately followed by the pointed data in their order of
+appearance in the structure, and the pointer value itself is ignored by the
+device, which must also return the value initially passed by the driver.
+
+\subparagraph{Handling of pointers to userspace memory}
+\label{sec:Device Types / Media Device / V4L2 ioctls / Userspace memory}
+
+A few pointers are special in that they point to userspace memory in the
+original V4L2 specification. They are:
+
+\begin{itemize}
+\item The \field{m.userptr} member of \textit{struct v4l2_buffer} and
+\href{https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/buffer.html#struct-v4l2-plane}{struct v4l2_plane}
+(technically an unsigned long, but designated a userspace address).
+\item The \field{ptr} member of \textit{struct v4l2_ext_ctrl}.
+\end{itemize}
+
+These pointers can cover large areas of scattered memory, which has the
+potential to require more descriptors than the virtio queue can provide. For
+these particular pointers only, a list of \textit{struct virtio_media_sg_entry}
+that covers the needed amount of memory for the pointer is used instead of
+using descriptors to map the pointed memory directly.
+
+\begin{lstlisting}
+struct virtio_media_sg_entry {
+	u64 start;
+	u32 len;
+	u32 __padding;
+};
+\end{lstlisting}
+
+For each such pointer to read, the device reads as many SG entries as needed
+to cover the length of the pointed buffer, as described by its parent
+structure (\field{length} member of \textit{struct v4l2_buffer} or
+\textit{struct v4l2_plane} for buffer memory, and \field{size} member of
+\textit{struct v4l2_ext_control} for control data).
+
+Since the device never needs to modify the list of SG entries, it is only
+provided by the driver in the device-readable section of the descriptor chain,
+and not repeated in the device-writable section, even for WR ioctls.
+
+\subparagraph{Unsupported ioctls}
+
+A few ioctls are replaced by other, more suitable mechanisms.
+
+\begin{itemize}
+\item \textit{VIDIOC_QUERYCAP} is replaced by reading the configuration area
+(see \ref{sec:Device Types / Media Device / Device Configuration Layout}).
+\item \textit{VIDIOC_DQBUF} is replaced by a dedicated event
+(see \ref{sec:Device Types / Media Device / Device Operation / Dequeue buffer}).
+\item \textit{VIDIOC_DQEVENT} is replaced by a dedicated event
+(see \ref{sec:Device Types / Media Device / Device Operation / Emit an event}).
+\item \textit{VIDIOC_G_JPEGCOMP} and \textit{VIDIOC_S_JPEGCOMP} are deprecated
+and replaced by the controls of the JPEG class.
+\item \textit{VIDIOC_LOG_STATUS} is a guest-only operation and shall not be
+implemented by the host.
+\end{itemize}
+
+\devicenormative{\subparagraph}{Device Operation: Unsupported ioctls}{Device Types / Media Device / Device Operation / Unsupported ioctls}
+
+If being requested an unsupported ioctl, the device MUST return the same
+error response as it would for an unknown ioctl, i.e. \textit{ENOTTY}.
+
+\paragraph{Device Operation: Mapping a MMAP buffer}
+
+\textbf{VIRTIO_MEDIA_CMD_MMAP} Command for mapping a MMAP buffer into the
+guest's address space.
+
+\begin{lstlisting}
+#define VIRTIO_MEDIA_MMAP_FLAG_RW (1 << 0)
+
+struct virtio_media_cmd_mmap {
+	struct virtio_media_cmd_header hdr;
+	u32 session_id;
+	u32 flags;
+	u64 offset;
+};
+\end{lstlisting}
+
+\begin{description}
+\item[\field{flags}] is the set of flags for the mapping. \field{VIRTIO_MEDIA_MMAP_FLAG_RW}
+can be set if a read-write mapping is desired. Without this flag the mapping
+will be read-only.
+\item[\field{offset}] corresponds to the \field{mem_offset} field of the
+\textit{union v4l2_plane} for the plane to map. This field can be obtained
+using the \textit{VIDIOC_QUERYBUF} ioctl.
+\end{description}
+
+The device responds to \textit{VIRTIO_MEDIA_CMD_MMAP} with \textit{virtio_media_resp_mmap}.
+
+\begin{lstlisting}
+struct virtio_media_resp_mmap {
+    struct virtio_media_resp_header hdr;
+    u64 addr;
+    u64 len;
+};
+\end{lstlisting}
+
+\begin{description}
+\item[\field{addr}] device physical address of the start of the mapping.
+\item[\field{len}] length of the mapping as indicated by the \textit{struct v4l2_plane}
+the buffer belongs to.
+\end{description}
+
+\paragraph{Device Operation: Unmapping a MMAP buffer}
+
+\textbf{VIRTIO_MEDIA_CMD_MUNMAP} Unmap a MMAP buffer previously mapped using \field{VIRTIO_MEDIA_CMD_MMAP}.
+
+\begin{lstlisting}
+struct virtio_media_cmd_munmap {
+    struct virtio_media_cmd_header hdr;
+    u64 guest_addr;
+};
+\end{lstlisting}
+
+\begin{description}
+\item[\field{guest_addr}] guest physical address previously returned by 
+\textit{VIRTIO_MEDIA_CMD_MMAP} at which the buffer has been previously mapped.
+\end{description}
+
+The device responds to \textit{VIRTIO_MEDIA_CMD_MUNMAP} with \textit{virtio_media_resp_munmap}.
+
+\begin{lstlisting}
+struct virtio_media_resp_munmap {
+    struct virtio_media_resp_header hdr;
+};
+\end{lstlisting}
+
+\devicenormative{\subparagraph}{Device Operation: Unmapping a MMAP buffer}{Device Types / Media Device / Device Operation / Unmapping a MMAP buffer}
+
+The device MUST keep mappings performed using \textit{VIRTIO_MEDIA_CMD_MMAP}
+valid until \textit{VIRTIO_MEDIA_CMD_MUNMAP} is called, even if the buffers or
+session they belong to are released or closed by the guest.
+
+\paragraph{Device Operation: Memory Types}
+
+The semantics of the three V4L2 memory types (\textit{MMAP}, \textit{USERPTR}
+and \textit{DMABUF}) can easily be mapped to a guest/host context.
+
+\subparagraph{MMAP}
+
+In virtio-media, \textit{MMAP} buffers are provisioned by the host, just like
+they are by the kernel in regular V4L2. Similarly to how userspace can map a
+\textit{MMAP} buffer into its address space using mmap and munmap, the
+virtio-media driver can map host buffers into the guest space by queueing the
+\textit{struct virtio_media_cmd_mmap} and \textit{struct virtio_media_cmd_munmap}
+commands to the commandq.
+
+\subparagraph{USERPTR}
+
+In virtio-media, \textit{USERPTR} buffers are provisioned by the guest, just
+like they are by userspace in regular V4L2. Instances of \textit{struct v4l2_buffer}
+and \textit{struct v4l2_plane} of this type are followed by a list of
+\textit{struct virtio_media_sg_entry}. For more information, see
+\ref{sec:Device Types / Media Device / V4L2 ioctls / Userspace memory}
+
+The host must not alter the pointer values provided by the guest, i.e.
+\field{the m.userptr} member of \textit{struct v4l2_buffer} and
+\textit{struct v4l2_plane} must be returned to the guest with the same value
+as it was provided.
+
+\subparagraph{DMABUF}
+
+In virtio-media, \textit{DMABUF} buffers are provisioned by a virtio object,
+just like they are by a \textit{DMABUF} in regular V4L2. Virtio objects are
+16-bytes UUIDs and do not fit in the placeholders for file descriptors, so
+they follow their embedding data structure as needed and the device must
+leave the V4L2 structure placeholder unchanged.
+
+Contrary to \textit{USERPTR} buffers, virtio objects UUIDs need to be added in
+both the device-readable and device-writable section of the descriptor chain.
+
+Host-allocated buffers with the \textit{V4L2_MEMORY_MMAP} memory type can also
+be exported as virtio objects for use with another virtio device using the
+\textit{VIDIOC_EXPBUF} ioctl. The fd placefolder of \textit{v4l2_exportbuffer}
+means that space for the UUID needs to be reserved right after that structure
+
+\subsubsection{Event Virtqueue}
+
+Events are a way for the device to inform the driver about asynchronous events
+that it should know about. In virtio-media, they are used as a replacement for
+the \textit{VIDIOC_DQBUF} and \textit{VIDIOC_DQEVENT} ioctls and the polling
+mechanism, which would be impractical to implement on top of virtio.
+
+\paragraph{Device Operation: Event header}
+
+\begin{lstlisting}
+#define VIRTIO_MEDIA_EVT_ERROR 0
+#define VIRTIO_MEDIA_EVT_DQBUF 1
+#define VIRTIO_MEDIA_EVT_EVENT 2
+
+/* Header for events queued by the device for the driver on the eventq. */
+struct virtio_media_event_header {
+    u32 event;
+    u32 session_id;
+};
+\end{lstlisting}
+
+\begin{description}
+\item[\field{event}] one of \field{VIRTIO_MEDIA_EVT_*}.
+\item[\field{session_id}] ID of the session the event applies to.
+\end{description}
+
+\paragraph{Device Operation: Device-side error}
+
+\textbf{VIRTIO_MEDIA_EVT_ERROR} Upon receiving this event, the session
+mentioned in the header is considered corrupted and automatically closed by
+the device.
+
+\begin{lstlisting}
+struct virtio_media_event_error {
+    struct virtio_media_event_header hdr;
+    u32 errno;
+    u32 __padding;
+};
+\end{lstlisting}
+
+\begin{description}
+\item[\field{errno}] error code describing the kind of error that occurred.
+\end{description}
+
+\paragraph{Device Operation: Dequeue buffer}
+\label{sec:Device Types / Media Device / Device Operation / Dequeue buffer}
+
+\textbf{VIRTIO_MEDIA_EVT_DQBUF} Signals that a buffer is not being used anymore
+by the device and is returned to the driver.
+
+A \textit{struct virtio_media_event_dqbuf} event is queued on the eventq by the
+device every time a buffer previously queued using the \textit{VIDIOC_QBUF}
+ioctl is done being processed and can be used by the driver again. This is like
+an implicit \textit{VIDIOC_DQBUF} ioctl.
+
+\begin{lstlisting}
+struct virtio_media_event_dqbuf {
+    struct virtio_media_event_header hdr;
+    struct v4l2_buffer buffer;
+    struct v4l2_plane planes[VIDEO_MAX_PLANES];
+};
+\end{lstlisting}
+
+\begin{description}
+\item[\field{buffer}] \textit{struct v4l2_buffer} describing the buffer that has been dequeued.
+\item[\field{planes}] array of \textit{struct v4l2_plane} containing the plane information for multi-planar buffers.
+\end{description}
+
+Pointer values in the \textit{struct v4l2_buffer} and \textit{struct v4l2_plane}
+are meaningless and must be ignored by the driver. It is recommended that the
+device sets them to NULL in order to avoid leaking potential host addresses.
+
+Note that in the case of a \field{USERPTR} buffer, the \textit{struct v4l2_buffer}
+used as event payload is not followed by the buffer memory: since that memory
+is the same that the driver submitted with the \textit{VIDIOC_QBUF}, it would
+be redundant to have it here.
+
+\paragraph{Device Operation: Emit an event}
+\label{sec:Device Types / Media Device / Device Operation / Emit an event}
+
+\textbf{VIRTIO_MEDIA_EVT_EVENT} Signals that a V4L2 event has been emitted for a session.
+
+A \textit{struct virtio_media_event_event} event is queued on the eventq by the
+device every time an event the driver previously subscribed to using the
+\textit{VIDIOC_SUBSCRIBE_EVENT} ioctl has been signaled. This is like an
+implicit \textit{VIDIOC_DQEVENT} ioctl.
+
+\begin{lstlisting}
+struct virtio_media_event_event {
+    struct virtio_media_event_header hdr;
+    struct v4l2_event event;
+};
+\end{lstlisting}
+
+\begin{description}
+\item[\field{event}] \textit{struct v4l2_event} describing the event that occurred.
+\end{description}
diff --git a/device-types/media/device-conformance.tex b/device-types/media/device-conformance.tex
new file mode 100644
index 0000000..3338822
--- /dev/null
+++ b/device-types/media/device-conformance.tex
@@ -0,0 +1,11 @@
+\conformance{\subsection}{Media Device Conformance}\label{sec:Conformance / Device Conformance / Media Device Conformance}
+
+A Media device MUST conform to the following normative statements:
+
+\begin{itemize}
+\item \ref{devicenormative:Device Types / Media Device / Virtqueues}
+\item \ref{devicenormative:Device Types / Media Device / Device Operation / Open device}
+\item \ref{devicenormative:Device Types / Media Device / Device Operation / V4L2 ioctls}
+\item \ref{devicenormative:Device Types / Media Device / Device Operation / Unsupported ioctls}
+\item \ref{devicenormative:Device Types / Media Device / Device Operation / Unmapping a MMAP buffer}
+\end{itemize}
\ No newline at end of file
diff --git a/device-types/media/driver-conformance.tex b/device-types/media/driver-conformance.tex
new file mode 100644
index 0000000..058b812
--- /dev/null
+++ b/device-types/media/driver-conformance.tex
@@ -0,0 +1,9 @@
+\conformance{\subsection}{Media Device Conformance}\label{sec:Conformance / Driver Conformance / Media Driver Conformance}
+
+A Media device MUST conform to the following normative statements:
+
+\begin{itemize}
+\item \ref{drivernormative:Device Types / Media Device / Virtqueues}
+\item \ref{drivernormative:Device Types / Media Device / Device Operation / Command Virtqueue}
+\item \ref{drivernormative:Device Types / Media Device / Device Operation / Close device}
+\end{itemize}
\ No newline at end of file
-- 
2.44.0

Re: [PATCH 1/1] virtio-media: Add virtio media device specification

[Michael S. Tsirkin]

On Fri, May 10, 2024 at 03:43:17PM +0200, Albert Esteve wrote:
> Virtio-media is an encapsulation of the V4L2 UAPI into
> virtio, able to virtualize any video device supported
> by V4L2
> 
> Note that virtio-media does not require the use of a
> V4L2 device driver or of Linux on the host or
> guest side - V4L2 is only used as a host-guest protocol,
> and both sides are free to convert it from/to any
> model that they wish to use.
> 
> Signed-off-by: Albert Esteve <aesteve@redhat.com>
> ---
>  conformance.tex                           |  13 +-
>  content.tex                               |   1 +
>  device-types/media/description.tex        | 574 ++++++++++++++++++++++
>  device-types/media/device-conformance.tex |  11 +
>  device-types/media/driver-conformance.tex |   9 +
>  5 files changed, 604 insertions(+), 4 deletions(-)
>  create mode 100644 device-types/media/description.tex
>  create mode 100644 device-types/media/device-conformance.tex
>  create mode 100644 device-types/media/driver-conformance.tex
> 
> diff --git a/conformance.tex b/conformance.tex
> index dc00e84..c369da1 100644
> --- a/conformance.tex
> +++ b/conformance.tex
> @@ -32,8 +32,10 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  \ref{sec:Conformance / Driver Conformance / Memory Driver Conformance},
>  \ref{sec:Conformance / Driver Conformance / I2C Adapter Driver Conformance},
>  \ref{sec:Conformance / Driver Conformance / SCMI Driver Conformance},
> -\ref{sec:Conformance / Driver Conformance / GPIO Driver Conformance} or
> -\ref{sec:Conformance / Driver Conformance / PMEM Driver Conformance}.
> +\ref{sec:Conformance / Driver Conformance / GPIO Driver Conformance},
> +\ref{sec:Conformance / Driver Conformance / PMEM Driver Conformance} or
> +\ref{sec:Conformance / Driver Conformance / Media Driver Conformance}.
> +
>  
>      \item Clause \ref{sec:Conformance / Legacy Interface: Transitional Device and Transitional Driver Conformance}.
>    \end{itemize}
> @@ -59,8 +61,9 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  \ref{sec:Conformance / Device Conformance / Memory Device Conformance},
>  \ref{sec:Conformance / Device Conformance / I2C Adapter Device Conformance},
>  \ref{sec:Conformance / Device Conformance / SCMI Device Conformance},
> -\ref{sec:Conformance / Device Conformance / GPIO Device Conformance} or
> -\ref{sec:Conformance / Device Conformance / PMEM Device Conformance}.
> +\ref{sec:Conformance / Device Conformance / GPIO Device Conformance},
> +\ref{sec:Conformance / Device Conformance / PMEM Device Conformance} or
> +\ref{sec:Conformance / Device Conformance / Media Device Conformance}.
>  
>      \item Clause \ref{sec:Conformance / Legacy Interface: Transitional Device and Transitional Driver Conformance}.
>    \end{itemize}
> @@ -152,6 +155,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  \input{device-types/scmi/driver-conformance.tex}
>  \input{device-types/gpio/driver-conformance.tex}
>  \input{device-types/pmem/driver-conformance.tex}
> +\input{device-types/media/driver-conformance.tex}
>  
>  \conformance{\section}{Device Conformance}\label{sec:Conformance / Device Conformance}
>  
> @@ -238,6 +242,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  \input{device-types/scmi/device-conformance.tex}
>  \input{device-types/gpio/device-conformance.tex}
>  \input{device-types/pmem/device-conformance.tex}
> +\input{device-types/media/device-conformance.tex}
>  
>  \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
> diff --git a/content.tex b/content.tex
> index 0a62dce..59925ae 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -767,6 +767,7 @@ \chapter{Device Types}\label{sec:Device Types}
>  \input{device-types/scmi/description.tex}
>  \input{device-types/gpio/description.tex}
>  \input{device-types/pmem/description.tex}
> +\input{device-types/media/description.tex}
>  
>  \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
>  
> diff --git a/device-types/media/description.tex b/device-types/media/description.tex
> new file mode 100644
> index 0000000..d67cc96
> --- /dev/null
> +++ b/device-types/media/description.tex
> @@ -0,0 +1,574 @@
> +\section{Media Device}\label{sec:Device Types / Media Device}
> +
> +The virtio media device follow the same model (and structures) as V4L2. It
> +can be used to virtualize cameras, codec devices, or any other device
> +supported by V4L2. The complete definition of V4L2 structures and ioctls can
> +be found under the
> +\href{https://www.kernel.org/doc/html/latest/userspace-api/media/index.html}{V4L2 UAPI documentation}.
> +
> +V4L2 is a UAPI that allows a less privileged entity (user-space) to use video
> +hardware exposed by a more privileged entity (the kernel). Virtio-media is an
> +encapsulation of this API into virtio, turning it into a virtualization API
> +for all classes of video devices supported by V4L2, where the host plays the
> +role of the kernel and the guest the role of user-space.
> +
> +The host is therefore responsible for presenting a virtual device that behaves
> +like an actual V4L2 device, which the guest can control.
> +
> +Note that virtio-media does not require the use of a V4L2 device driver or of
> +Linux on the host or guest side - V4L2 is only used as a host-guest protocol,
> +and both sides are free to convert it from/to any model that they wish to use.
> +
> +This section relies on definitions from
> +\href{https://www.kernel.org/doc/html/latest/userspace-api/media/index.html}{V4L2 UAPI documentation}.
> +

We should generally avoid host/guest terminology, except as an example.

Also when encapsulating UAPIs, endian-ness generally becomes a problem.
What's the approach here?

> +\subsection{Device ID}\label{sec:Device Types / Media Device / Device ID}
> +
> +42
> +
> +\subsection{Virtqueues}\label{sec:Device Types / Media Device / Virtqueues}
> +
> +\begin{description}
> +\item[0] commandq - used for driver commands and device responses to these
> +commands.
> +\item[1] eventq - used for events sent by the device to the driver.
> +\end{description}
> +
> +\devicenormative{\subsubsection}{Virtqueues}{Device Types / Media Device / Virtqueues}
> +
> +The device MUST return the descriptor chains it receives on the commandq as
> +soon as possible, and must never hold them for indefinite periods of time.
> +
> +\drivernormative{\subsubsection}{Virtqueues}{Device Types / Media Device / Virtqueues}
> +
> +The driver MUST re-queue the descriptor chains returned by the device on the
> +eventq as soon as possible, and must never hold them for indefinite periods
> +of time.
> +
> +\subsection{Feature Bits}\label{sec:Device Types / Media Device / Feature Bits}
> +
> +None
> +
> +\subsection{Device Configuration Layout}\label{sec:Device Types / Media Device / Device Configuration Layout}
> +
> +The video device configuration space uses the following layout:
> +
> +\begin{lstlisting}
> +struct virtio_media_config {
> +    le32 device_caps;
> +    le32 device_type;
> +    u8 card[32];
> +};
> +\end{lstlisting}
> +
> +\begin{description}
> +\item[\field{device_caps}] (driver-read-only) flags representing the device
> +capabilities as used in
> +\href{https://www.kernel.org/doc/html/v4.9/media/uapi/v4l/vidioc-querycap.html#c.v4l2_capability}{struct v4l2_capabilities}.
> +Corresponds with the \field{device_caps} field in the \textit{struct video_device}.
> +\item[\field{device_type}] (driver-read-only) informs the driver of the type
> +of the video device. Corresponds with the \field{vfl_devnode_type} field of the device.
> +\item[\field{card}] (driver-read-only) name of the device, a NUL-terminated
> +UTF-8 string. Corresponds with the \field{card} field of the \textit{struct v4l2_capability}.
> +If all the characters of the field are used, it does not need to be NUL-terminated.
> +\end{description}
> +
> +\subsection{Device Initialization}
> +
> +\begin{enumerate}
> +\item The driver reads the \field{device_caps} and \field{device_type} fields
> +from the configuration layout to identify the device.
> +\item The driver sets up the \field{commandq} and \field{eventq}.
> +\item The driver may open a session to use the device and send V4L2 ioctls in
> +order to receive more information about the device, such as supported
> +formats or controls.
> +\end{enumerate}
> +
> +\subsection{Device Operation}\label{sec:Device Types / Media Device / Device Operation}
> +
> +Commands are queued on the command queue by the driver for the device to
> +process. The errors returned by each command are standard
> +\href{https://www.kernel.org/doc/html/latest/userspace-api/media/gen-errors.html}{Linux kernel error codes}.
> +For instance, a command that contains invalid options will return \textit{EINVAL}.
> +
> +Events are sent on the event queue by the device for the driver to handle.
> +
> +\subsubsection{Command Virtqueue}
> +
> +\paragraph{Device Operation: Command headers}
> +
> +\begin{lstlisting}
> +#define VIRTIO_MEDIA_CMD_OPEN 1
> +#define VIRTIO_MEDIA_CMD_CLOSE 2
> +#define VIRTIO_MEDIA_CMD_IOCTL 3
> +#define VIRTIO_MEDIA_CMD_MMAP 4
> +#define VIRTIO_MEDIA_CMD_MUNMAP 5
> +
> +/* Header for all virtio commands from the driver to the device on the commandq. */
> +struct virtio_media_cmd_header {
> +	u32 cmd;
> +	u32 __padding;
> +};
> +
> +/* Header for all virtio responses from the device to the driver on the commandq. */
> +struct virtio_media_resp_header {
> +	u32 status;
> +	u32 __padding;
> +};
> +\end{lstlisting}
> +
> +A command consists of a command header \textit{virtio_media_cmd_header}
> +containing the following device-readable field:
> +
> +\begin{description}
> +\item[\field{cmd}] specifies a device request type (VIRTIO_MEDIA_CMD_*).
> +\end{description}
> +
> +A response consists of a response header \textit{virtio_media_resp_header}
> +containing the following device-writable field:
> +
> +\begin{description}
> +\item[\field{status}] indicates a device request status.
> +\end{description}
> +
> +The status field can take 0 if the command was successful, or one of the
> +standard Linux error codes if it was not.
> +
> +\drivernormative{\paragraph}{Device Operation: Command Virtqueue: Sessions}{Device Types / Media Device / Device Operation / Command Virtqueue}
> +
> +Sessions are how the device is multiplexed, allowing several distinct works to
> +take place simultaneously. The driver needs to open a session before it can
> +perform any useful operation on the device.
> +
> +\paragraph{Device Operation: Open device}
> +
> +\textbf{VIRTIO_MEDIA_CMD_OPEN} Command for creating a new session.
> +
> +This is the equivalent of calling \textit{open} on a V4L2 device node.
> +The driver uses \textit{virtio_media_cmd_open} to send an open request.
> +
> +\begin{lstlisting}
> +struct virtio_media_cmd_open {
> +    struct virtio_media_cmd_header hdr;
> +};
> +\end{lstlisting}
> +
> +The device responds to \textit{VIRTIO_MEDIA_CMD_OPEN} with \textit{virtio_media_resp_open}.
> +
> +\begin{lstlisting}
> +struct virtio_media_resp_open {
> +    struct virtio_media_resp_header hdr;
> +    u32 session_id;
> +    u32 __padding;
> +};
> +\end{lstlisting}
> +
> +\begin{description}
> +\item[\field{session_id}] specifies an identifier for the current session. The
> +identifier can be used to perform other commands on the session, notably ioctls.
> +\end{description}
> +
> +\devicenormative{\subparagraph}{Device Operation: Open device}{Device Types / Media Device / Device Operation / Open device}
> +
> +Upon success, the device MUST set a \field{session_id} in \textit{virtio_media_resp_open}
> +to an integer that is NOT used by any other open session.
> +
> +\paragraph{Device Operation: Close device}
> +
> +\textbf{VIRTIO_MEDIA_CMD_CLOSE} Command for closing an active session.
> +
> +This is the equivalent of calling \textit{close} on a previously opened V4L2
> +device node. All resources associated with this session will be freed.
> +
> +This command does not require a response from the device.
> +
> +\begin{lstlisting}
> +struct virtio_media_cmd_close {
> +    struct virtio_media_cmd_header hdr;
> +    u32 session_id;
> +    u32 __padding;
> +};
> +\end{lstlisting}
> +
> +\begin{description}
> +\item[\field{session_id}] specifies an identifier for the session to close.
> +\end{description}
> +
> +\drivernormative{\subparagraph}{Device Operation: Close device}{Device Types / Media Device / Device Operation / Close device}
> +
> +The session ID SHALL NOT be used again after queueing this command.
> +
> +\paragraph{Device Operation: V4L2 ioctls}
> +
> +\textbf{VIRTIO_MEDIA_CMD_IOCTL} Command for executing an ioctl on an open
> +session.
> +
> +This command asks the device to run one of the `VIDIOC_*` ioctls on the active
> +session.
> +
> +\begin{lstlisting}
> +struct virtio_media_cmd_ioctl {
> +    struct virtio_media_cmd_header hdr;
> +    u32 session_id;
> +    u32 code;
> +    /* Followed by the relevant ioctl payload as defined in the macro */
> +};
> +\end{lstlisting}
> +
> +\begin{description}
> +\item[\field{session_id}] specifies an identifier of thesession to run the ioctl on.
> +\item[\field{code}] specifies the code of the \field{VIDIOC_*} ioctl to run.
> +\end{description}
> +
> +The code is extracted from the
> +\href{https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/videodev.html}{videodev2.h},
> +header file. The file defines the ioctl's codes, type of payload, and
> +direction. The code consists of the second argument of the \field{_IO*} macro.
> +
> +For example, the \textit{VIDIOC_G_FMT} is defined as follows:
> +
> +\begin{lstlisting}
> +#define VIDIOC_G_FMT _IOWR('V',  4, struct v4l2_format)
> +\end{lstlisting}
> +
> +This means that its ioctl code is \textit{4}, that its payload is a
> +\textit{struct v4l2_format}, and that its direction is \textit{WR} (i.e., the
> +payload is written by both the driver and the device).
> +See Section \ref{sec:Device Types / Media Device / V4L2 ioctls / Ioctls payload}
> +for more information about the direction of ioctls.
> +
> +The payload layout is always a 64-bit representation of the corresponding
> +V4L2 structure, irrespective of the host and guest architecture.
> +
> +The device responds to \textit{VIRTIO_MEDIA_CMD_IOCTL} with \textit{virtio_media_resp_ioctl}.
> +
> +\begin{lstlisting}
> +struct virtio_media_resp_ioctl {
> +    struct virtio_media_resp_header hdr;
> +    /* Followed by the ioctl payload as defined in the macro */
> +};
> +\end{lstlisting}
> +
> +\subparagraph{Ioctls payload}\label{sec:Device Types / Media Device / V4L2 ioctls / Ioctls payload}
> +
> +Each ioctl has a payload, which is defined by the third argument of the
> +\field{_IO*} macro defining it. 
> +
> +The payload of an ioctl in the descriptor chain follows the command structure,
> +the reponse structure, or both depending on the direction:
> +
> +\begin{itemize}
> +\item \textbf{_IOR} is read-only for the driver, meaning the payload
> +follows the response in the device-writable section of the descriptor chain.
> +\item \textbf{_IOW} is read-only for the device, meaning the payload
> +follows the command in the driver-writable section of the descriptor chain.
> +\item \textbf{_IOWR} is writable by both the device and driver,
> +meaning the payload must follow both the command in the driver-writable section
> +of the descriptor chain, and the response in the device-writable section.
> +\end{itemize}
> +
> +A common optimization for \textit{WR} ioctls is to provide the payload using
> +descriptors that both point to the same buffer. This mimics the behavior of
> +V4L2 ioctls where the data is only passed once and used as both input and
> +output by the kernel.
> +
> +\devicenormative{\subparagraph}{Device Operation: V4L2 ioctls}{Device Types / Media Device / Device Operation / V4L2 ioctls}
> +
> +In case of success of a device-writable ioctl, the device MUST always write the
> +payload in the device-writable part of the descriptor chain.
> +
> +In case of failure of a device-writable ioctl, the device is free to write the
> +payload in the device-writable part of the descriptor chain or not. Some errors
> +may still result in the payload being updated, and in this case the device is
> +expected to write the updated payload. If the device has not written the
> +payload after an error, the driver MUST assume that the payload has not been
> +modified.
> +
> +\subparagraph{Handling of pointers in ioctl payload}
> +
> +A few structures used as ioctl payloads contain pointers to further
> +data needed for the ioctl. There are notably:
> +
> +\begin{itemize}
> +\item The \field{planes} pointer of
> +\href{https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/buffer.html#struct-v4l2-buffer}{struct v4l2_buffer},
> +which size is determined by the length member.
> +\item The \field{controls} pointer of \textit{struct v4l2_ext_controls}, which
> +size is determined by the count member.
> +\end{itemize}
> +
> +If the size of the pointed area is determined to be non-zero, then the main
> +payload is immediately followed by the pointed data in their order of
> +appearance in the structure, and the pointer value itself is ignored by the
> +device, which must also return the value initially passed by the driver.
> +
> +\subparagraph{Handling of pointers to userspace memory}
> +\label{sec:Device Types / Media Device / V4L2 ioctls / Userspace memory}
> +
> +A few pointers are special in that they point to userspace memory in the
> +original V4L2 specification. They are:
> +
> +\begin{itemize}
> +\item The \field{m.userptr} member of \textit{struct v4l2_buffer} and
> +\href{https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/buffer.html#struct-v4l2-plane}{struct v4l2_plane}
> +(technically an unsigned long, but designated a userspace address).
> +\item The \field{ptr} member of \textit{struct v4l2_ext_ctrl}.
> +\end{itemize}
> +
> +These pointers can cover large areas of scattered memory, which has the
> +potential to require more descriptors than the virtio queue can provide. For
> +these particular pointers only, a list of \textit{struct virtio_media_sg_entry}
> +that covers the needed amount of memory for the pointer is used instead of
> +using descriptors to map the pointed memory directly.
> +
> +\begin{lstlisting}
> +struct virtio_media_sg_entry {
> +	u64 start;
> +	u32 len;
> +	u32 __padding;
> +};
> +\end{lstlisting}
> +
> +For each such pointer to read, the device reads as many SG entries as needed
> +to cover the length of the pointed buffer, as described by its parent
> +structure (\field{length} member of \textit{struct v4l2_buffer} or
> +\textit{struct v4l2_plane} for buffer memory, and \field{size} member of
> +\textit{struct v4l2_ext_control} for control data).
> +
> +Since the device never needs to modify the list of SG entries, it is only
> +provided by the driver in the device-readable section of the descriptor chain,
> +and not repeated in the device-writable section, even for WR ioctls.
> +
> +\subparagraph{Unsupported ioctls}
> +
> +A few ioctls are replaced by other, more suitable mechanisms.
> +
> +\begin{itemize}
> +\item \textit{VIDIOC_QUERYCAP} is replaced by reading the configuration area
> +(see \ref{sec:Device Types / Media Device / Device Configuration Layout}).
> +\item \textit{VIDIOC_DQBUF} is replaced by a dedicated event
> +(see \ref{sec:Device Types / Media Device / Device Operation / Dequeue buffer}).
> +\item \textit{VIDIOC_DQEVENT} is replaced by a dedicated event
> +(see \ref{sec:Device Types / Media Device / Device Operation / Emit an event}).
> +\item \textit{VIDIOC_G_JPEGCOMP} and \textit{VIDIOC_S_JPEGCOMP} are deprecated
> +and replaced by the controls of the JPEG class.
> +\item \textit{VIDIOC_LOG_STATUS} is a guest-only operation and shall not be
> +implemented by the host.
> +\end{itemize}
> +
> +\devicenormative{\subparagraph}{Device Operation: Unsupported ioctls}{Device Types / Media Device / Device Operation / Unsupported ioctls}
> +
> +If being requested an unsupported ioctl, the device MUST return the same
> +error response as it would for an unknown ioctl, i.e. \textit{ENOTTY}.
> +
> +\paragraph{Device Operation: Mapping a MMAP buffer}
> +
> +\textbf{VIRTIO_MEDIA_CMD_MMAP} Command for mapping a MMAP buffer into the
> +guest's address space.
> +
> +\begin{lstlisting}
> +#define VIRTIO_MEDIA_MMAP_FLAG_RW (1 << 0)
> +
> +struct virtio_media_cmd_mmap {
> +	struct virtio_media_cmd_header hdr;
> +	u32 session_id;
> +	u32 flags;
> +	u64 offset;
> +};
> +\end{lstlisting}
> +
> +\begin{description}
> +\item[\field{flags}] is the set of flags for the mapping. \field{VIRTIO_MEDIA_MMAP_FLAG_RW}
> +can be set if a read-write mapping is desired. Without this flag the mapping
> +will be read-only.
> +\item[\field{offset}] corresponds to the \field{mem_offset} field of the
> +\textit{union v4l2_plane} for the plane to map. This field can be obtained
> +using the \textit{VIDIOC_QUERYBUF} ioctl.
> +\end{description}
> +
> +The device responds to \textit{VIRTIO_MEDIA_CMD_MMAP} with \textit{virtio_media_resp_mmap}.
> +
> +\begin{lstlisting}
> +struct virtio_media_resp_mmap {
> +    struct virtio_media_resp_header hdr;
> +    u64 addr;
> +    u64 len;
> +};
> +\end{lstlisting}
> +
> +\begin{description}
> +\item[\field{addr}] device physical address of the start of the mapping.
> +\item[\field{len}] length of the mapping as indicated by the \textit{struct v4l2_plane}
> +the buffer belongs to.
> +\end{description}
> +
> +\paragraph{Device Operation: Unmapping a MMAP buffer}
> +
> +\textbf{VIRTIO_MEDIA_CMD_MUNMAP} Unmap a MMAP buffer previously mapped using \field{VIRTIO_MEDIA_CMD_MMAP}.
> +
> +\begin{lstlisting}
> +struct virtio_media_cmd_munmap {
> +    struct virtio_media_cmd_header hdr;
> +    u64 guest_addr;
> +};
> +\end{lstlisting}
> +
> +\begin{description}
> +\item[\field{guest_addr}] guest physical address previously returned by 
> +\textit{VIRTIO_MEDIA_CMD_MMAP} at which the buffer has been previously mapped.
> +\end{description}
> +
> +The device responds to \textit{VIRTIO_MEDIA_CMD_MUNMAP} with \textit{virtio_media_resp_munmap}.
> +
> +\begin{lstlisting}
> +struct virtio_media_resp_munmap {
> +    struct virtio_media_resp_header hdr;
> +};
> +\end{lstlisting}
> +
> +\devicenormative{\subparagraph}{Device Operation: Unmapping a MMAP buffer}{Device Types / Media Device / Device Operation / Unmapping a MMAP buffer}
> +
> +The device MUST keep mappings performed using \textit{VIRTIO_MEDIA_CMD_MMAP}
> +valid until \textit{VIRTIO_MEDIA_CMD_MUNMAP} is called, even if the buffers or
> +session they belong to are released or closed by the guest.
> +
> +\paragraph{Device Operation: Memory Types}
> +
> +The semantics of the three V4L2 memory types (\textit{MMAP}, \textit{USERPTR}
> +and \textit{DMABUF}) can easily be mapped to a guest/host context.
> +
> +\subparagraph{MMAP}
> +
> +In virtio-media, \textit{MMAP} buffers are provisioned by the host, just like
> +they are by the kernel in regular V4L2. Similarly to how userspace can map a
> +\textit{MMAP} buffer into its address space using mmap and munmap, the
> +virtio-media driver can map host buffers into the guest space by queueing the
> +\textit{struct virtio_media_cmd_mmap} and \textit{struct virtio_media_cmd_munmap}
> +commands to the commandq.
> +
> +\subparagraph{USERPTR}
> +
> +In virtio-media, \textit{USERPTR} buffers are provisioned by the guest, just
> +like they are by userspace in regular V4L2. Instances of \textit{struct v4l2_buffer}
> +and \textit{struct v4l2_plane} of this type are followed by a list of
> +\textit{struct virtio_media_sg_entry}. For more information, see
> +\ref{sec:Device Types / Media Device / V4L2 ioctls / Userspace memory}
> +
> +The host must not alter the pointer values provided by the guest, i.e.
> +\field{the m.userptr} member of \textit{struct v4l2_buffer} and
> +\textit{struct v4l2_plane} must be returned to the guest with the same value
> +as it was provided.
> +
> +\subparagraph{DMABUF}
> +
> +In virtio-media, \textit{DMABUF} buffers are provisioned by a virtio object,
> +just like they are by a \textit{DMABUF} in regular V4L2. Virtio objects are
> +16-bytes UUIDs and do not fit in the placeholders for file descriptors, so
> +they follow their embedding data structure as needed and the device must
> +leave the V4L2 structure placeholder unchanged.
> +
> +Contrary to \textit{USERPTR} buffers, virtio objects UUIDs need to be added in
> +both the device-readable and device-writable section of the descriptor chain.
> +
> +Host-allocated buffers with the \textit{V4L2_MEMORY_MMAP} memory type can also
> +be exported as virtio objects for use with another virtio device using the
> +\textit{VIDIOC_EXPBUF} ioctl. The fd placefolder of \textit{v4l2_exportbuffer}
> +means that space for the UUID needs to be reserved right after that structure
> +
> +\subsubsection{Event Virtqueue}
> +
> +Events are a way for the device to inform the driver about asynchronous events
> +that it should know about. In virtio-media, they are used as a replacement for
> +the \textit{VIDIOC_DQBUF} and \textit{VIDIOC_DQEVENT} ioctls and the polling
> +mechanism, which would be impractical to implement on top of virtio.
> +
> +\paragraph{Device Operation: Event header}
> +
> +\begin{lstlisting}
> +#define VIRTIO_MEDIA_EVT_ERROR 0
> +#define VIRTIO_MEDIA_EVT_DQBUF 1
> +#define VIRTIO_MEDIA_EVT_EVENT 2
> +
> +/* Header for events queued by the device for the driver on the eventq. */
> +struct virtio_media_event_header {
> +    u32 event;
> +    u32 session_id;
> +};
> +\end{lstlisting}
> +
> +\begin{description}
> +\item[\field{event}] one of \field{VIRTIO_MEDIA_EVT_*}.
> +\item[\field{session_id}] ID of the session the event applies to.
> +\end{description}
> +
> +\paragraph{Device Operation: Device-side error}
> +
> +\textbf{VIRTIO_MEDIA_EVT_ERROR} Upon receiving this event, the session
> +mentioned in the header is considered corrupted and automatically closed by
> +the device.
> +
> +\begin{lstlisting}
> +struct virtio_media_event_error {
> +    struct virtio_media_event_header hdr;
> +    u32 errno;
> +    u32 __padding;
> +};
> +\end{lstlisting}
> +
> +\begin{description}
> +\item[\field{errno}] error code describing the kind of error that occurred.
> +\end{description}
> +
> +\paragraph{Device Operation: Dequeue buffer}
> +\label{sec:Device Types / Media Device / Device Operation / Dequeue buffer}
> +
> +\textbf{VIRTIO_MEDIA_EVT_DQBUF} Signals that a buffer is not being used anymore
> +by the device and is returned to the driver.
> +
> +A \textit{struct virtio_media_event_dqbuf} event is queued on the eventq by the
> +device every time a buffer previously queued using the \textit{VIDIOC_QBUF}
> +ioctl is done being processed and can be used by the driver again. This is like
> +an implicit \textit{VIDIOC_DQBUF} ioctl.
> +
> +\begin{lstlisting}
> +struct virtio_media_event_dqbuf {
> +    struct virtio_media_event_header hdr;
> +    struct v4l2_buffer buffer;
> +    struct v4l2_plane planes[VIDEO_MAX_PLANES];
> +};
> +\end{lstlisting}
> +
> +\begin{description}
> +\item[\field{buffer}] \textit{struct v4l2_buffer} describing the buffer that has been dequeued.
> +\item[\field{planes}] array of \textit{struct v4l2_plane} containing the plane information for multi-planar buffers.
> +\end{description}
> +
> +Pointer values in the \textit{struct v4l2_buffer} and \textit{struct v4l2_plane}
> +are meaningless and must be ignored by the driver. It is recommended that the
> +device sets them to NULL in order to avoid leaking potential host addresses.
> +
> +Note that in the case of a \field{USERPTR} buffer, the \textit{struct v4l2_buffer}
> +used as event payload is not followed by the buffer memory: since that memory
> +is the same that the driver submitted with the \textit{VIDIOC_QBUF}, it would
> +be redundant to have it here.
> +
> +\paragraph{Device Operation: Emit an event}
> +\label{sec:Device Types / Media Device / Device Operation / Emit an event}
> +
> +\textbf{VIRTIO_MEDIA_EVT_EVENT} Signals that a V4L2 event has been emitted for a session.
> +
> +A \textit{struct virtio_media_event_event} event is queued on the eventq by the
> +device every time an event the driver previously subscribed to using the
> +\textit{VIDIOC_SUBSCRIBE_EVENT} ioctl has been signaled. This is like an
> +implicit \textit{VIDIOC_DQEVENT} ioctl.
> +
> +\begin{lstlisting}
> +struct virtio_media_event_event {
> +    struct virtio_media_event_header hdr;
> +    struct v4l2_event event;
> +};
> +\end{lstlisting}
> +
> +\begin{description}
> +\item[\field{event}] \textit{struct v4l2_event} describing the event that occurred.
> +\end{description}
> diff --git a/device-types/media/device-conformance.tex b/device-types/media/device-conformance.tex
> new file mode 100644
> index 0000000..3338822
> --- /dev/null
> +++ b/device-types/media/device-conformance.tex
> @@ -0,0 +1,11 @@
> +\conformance{\subsection}{Media Device Conformance}\label{sec:Conformance / Device Conformance / Media Device Conformance}
> +
> +A Media device MUST conform to the following normative statements:
> +
> +\begin{itemize}
> +\item \ref{devicenormative:Device Types / Media Device / Virtqueues}
> +\item \ref{devicenormative:Device Types / Media Device / Device Operation / Open device}
> +\item \ref{devicenormative:Device Types / Media Device / Device Operation / V4L2 ioctls}
> +\item \ref{devicenormative:Device Types / Media Device / Device Operation / Unsupported ioctls}
> +\item \ref{devicenormative:Device Types / Media Device / Device Operation / Unmapping a MMAP buffer}
> +\end{itemize}
> \ No newline at end of file
> diff --git a/device-types/media/driver-conformance.tex b/device-types/media/driver-conformance.tex
> new file mode 100644
> index 0000000..058b812
> --- /dev/null
> +++ b/device-types/media/driver-conformance.tex
> @@ -0,0 +1,9 @@
> +\conformance{\subsection}{Media Device Conformance}\label{sec:Conformance / Driver Conformance / Media Driver Conformance}
> +
> +A Media device MUST conform to the following normative statements:
> +
> +\begin{itemize}
> +\item \ref{drivernormative:Device Types / Media Device / Virtqueues}
> +\item \ref{drivernormative:Device Types / Media Device / Device Operation / Command Virtqueue}
> +\item \ref{drivernormative:Device Types / Media Device / Device Operation / Close device}
> +\end{itemize}
> \ No newline at end of file
> -- 
> 2.44.0

Re: [PATCH 0/1] virtio-media: Add device specification

[Alexander Gordeev]

+CC Matti

Hi Albert,

On 10.05.24 15:43, Albert Esteve wrote:
> Hi,
> 
> This a formal attempt of including virtio-media
> device specification.
> 
> Virtio-media came from a discussion on virtio-dev
> mailing list, which lead to presenting virtio-v4l2[1]
> specification as an alternative to virtio-video.
> 
> Later, virtio-v4l2 was renamed to virtio-media[2]
> and published through:
> 
> https://github.com/chromeos/virtio-media
> 
> The repository above includes a guest V4L2 driver able
> to pass v4l2-compliance when proxying the vivid/vicodec
> virtual devices or an actual UVC camera using the
> crosvm V4L2 proxy device. Steps to reproduce are
> also detailed[3].
> 
> There is some overlap with virtio-video in regards
> to which devices it can handle. However,
> as virtio-media will likely be the virtualization
> solution for ChromeOS (already landed into the chromeos
> organization) and possibly other Google projects for
> media devices, it would be desirable to include the
> specification in the next virtio release despite
> the aforementioned overlap.

Well, last year Cornelia made it clear, that this kind of overlap is not 
desirable in the specification. After long email discussion we had a 
video call with some selected experts on June 1st discussing the 
proposed approaches. The conclusion was that virtio-video development 
should be continued, that the virtio-v4l2 use-case is valid, but the 
proposed approach is not desirable in the specification, it should be 
instead implemented with multiple device types. It was also concluded, 
that a new device ID should not be reserved. It is a pity, that there 
were no public announcement after that, so now it looks like we're going 
to have the same debate again. But I'll be happy to discuss all of this 
with Albert and the new joiners in the discussion. I believe my 
arguments are still valid.

I suggest, that at least both of us (and hopefully others) start with 
familiarizing ourselves with both virtio-video and virtio-media. I'd be 
happy to present the current state of the virtio-video spec in details 
and answer questions in a video call. I think, I'll need two weeks to 
prepare. Maybe we can even resolve the issue ourselves. I think that 
would be a good start. WDYT?

> The device ID in this document differs from
> the ID in the virtio-media project repository.
> And it will probably need some discussion on which
> would be the correct definitive ID.
> 
> Full PDF: https://drive.google.com/file/d/1PG1YxzbSvQHPphFhbUKyKKdvuwO6shyi/view?usp=sharing
> PDF with the media section only: https://drive.google.com/file/d/1Y7kAGzlUfl30VIUx9wQtz5sFTkWnBiyA/view?usp=sharing
> 
> [1] https://mail.google.com/mail/u/0?ui=2&ik=73ebd65ebd&attid=0.1&permmsgid=msg-f:1767388565327924962&th=1887068940754ee2&view=att&disp=inline&realattid=f_libalimc0
> [2] https://www.mail-archive.com/virtio-dev@lists.oasis-open.org/msg12665.html
> [3] https://github.com/chromeos/virtio-media/blob/main/TRY_IT_OUT.md
> 
> Albert Esteve (1):
>    virtio-media: Add virtio media device specification
> 
>   conformance.tex                           |  13 +-
>   content.tex                               |   1 +
>   device-types/media/description.tex        | 574 ++++++++++++++++++++++
>   device-types/media/device-conformance.tex |  11 +
>   device-types/media/driver-conformance.tex |   9 +
>   5 files changed, 604 insertions(+), 4 deletions(-)
>   create mode 100644 device-types/media/description.tex
>   create mode 100644 device-types/media/device-conformance.tex
>   create mode 100644 device-types/media/driver-conformance.tex
> 

Kind regards

-- 
Alexander Gordeev
Senior Software Engineer

OpenSynergy GmbH
Rotherstr. 20, 10245 Berlin
www.opensynergy.com

Re: [PATCH 0/1] virtio-media: Add device specification

[Alexander Gordeev]

On 13.05.24 13:18, Albert Esteve wrote:
> 
> 
> On Mon, May 13, 2024 at 11:56 AM Alexander Gordeev 
> <alexander.gordeev@opensynergy.com 
> <mailto:alexander.gordeev@opensynergy.com>> wrote:
> 
>     +CC Matti
> 
>     Hi Albert,
> 
>     On 10.05.24 15:43, Albert Esteve wrote:
>      > Hi,
>      >
>      > This a formal attempt of including virtio-media
>      > device specification.
>      >
>      > Virtio-media came from a discussion on virtio-dev
>      > mailing list, which lead to presenting virtio-v4l2[1]
>      > specification as an alternative to virtio-video.
>      >
>      > Later, virtio-v4l2 was renamed to virtio-media[2]
>      > and published through:
>      >
>      > https://github.com/chromeos/virtio-media
>     <https://github.com/chromeos/virtio-media>
>      >
>      > The repository above includes a guest V4L2 driver able
>      > to pass v4l2-compliance when proxying the vivid/vicodec
>      > virtual devices or an actual UVC camera using the
>      > crosvm V4L2 proxy device. Steps to reproduce are
>      > also detailed[3].
>      >
>      > There is some overlap with virtio-video in regards
>      > to which devices it can handle. However,
>      > as virtio-media will likely be the virtualization
>      > solution for ChromeOS (already landed into the chromeos
>      > organization) and possibly other Google projects for
>      > media devices, it would be desirable to include the
>      > specification in the next virtio release despite
>      > the aforementioned overlap.
> 
>     Well, last year Cornelia made it clear, that this kind of overlap is
>     not
>     desirable in the specification. After long email discussion we had a
>     video call with some selected experts on June 1st discussing the
>     proposed approaches. The conclusion was that virtio-video development
>     should be continued, that the virtio-v4l2 use-case is valid, but the
>     proposed approach is not desirable in the specification, it should be
>     instead implemented with multiple device types. It was also concluded,
>     that a new device ID should not be reserved. It is a pity, that there
>     were no public announcement after that, so now it looks like we're
>     going
>     to have the same debate again. But I'll be happy to discuss all of this
>     with Albert and the new joiners in the discussion. I believe my
>     arguments are still valid.
> 
> 
> Hi Alexander,
> 
> My intention is not to re-open the debate. The debate already happened
> and the points given were clear enough. I will certainly noy be able to
> enrich the debate with my own points. Sadly, we did not get a clear
> conclusion, nor an agreement, on the way to move forward.
> Instead, we ended up with two different specifications, one
> that is still working towards standarization, one that did not.
> 
> I completely agree with Cornelia, the overlap is not desirable. I
> really wish there had been an agreement and moved together
> towards a common goal. But alas, that did not happen. And I
> think that having a non-standard virtual device used in some
> systems is the worst case, and hence decided to attempt
> standardization.

Thanks for the clarification!
Yeah, I also wish we could move together to a common goal. But it looks 
like we have different sets of requirements and therefore quite 
different short term goals. I hope virtio-video can become suitable for 
all of us in the long term, if there is also the virtio-camera, so that 
the compatibility is much less a problem.

>     I suggest, that at least both of us (and hopefully others) start with
>     familiarizing ourselves with both virtio-video and virtio-media. I'd be
>     happy to present the current state of the virtio-video spec in details
>     and answer questions in a video call. I think, I'll need two weeks to
>     prepare. Maybe we can even resolve the issue ourselves. I think that
>     would be a good start. WDYT?
> 
> 
> I am more or less familiar with virtio-video (not so much in the latest
> drops, but I still checked them). But I do not own virtio-media, or have
> any intellectual involvement in its design. I merely followed its
> progress, and decided to collect the specification written at
> https://github.com/chromeos/virtio-media 
> <https://github.com/chromeos/virtio-media>.
> 
> So I am in no position to solve the issue. But I decided to try
> and alleviate its impact by having both in the standard.
> 
> That said, I will read your next virtio-video drop and try to
> provide feedback :)

Thanks, looking forward to your feedback. :)

> BR,
> Albert
> 
> 
>      > The device ID in this document differs from
>      > the ID in the virtio-media project repository.
>      > And it will probably need some discussion on which
>      > would be the correct definitive ID.
>      >
>      > Full PDF:
>     https://drive.google.com/file/d/1PG1YxzbSvQHPphFhbUKyKKdvuwO6shyi/view?usp=sharing <https://drive.google.com/file/d/1PG1YxzbSvQHPphFhbUKyKKdvuwO6shyi/view?usp=sharing>
>      > PDF with the media section only:
>     https://drive.google.com/file/d/1Y7kAGzlUfl30VIUx9wQtz5sFTkWnBiyA/view?usp=sharing <https://drive.google.com/file/d/1Y7kAGzlUfl30VIUx9wQtz5sFTkWnBiyA/view?usp=sharing>
>      >
>      > [1]
>     https://mail.google.com/mail/u/0?ui=2&ik=73ebd65ebd&attid=0.1&permmsgid=msg-f:1767388565327924962&th=1887068940754ee2&view=att&disp=inline&realattid=f_libalimc0 <https://mail.google.com/mail/u/0?ui=2&ik=73ebd65ebd&attid=0.1&permmsgid=msg-f:1767388565327924962&th=1887068940754ee2&view=att&disp=inline&realattid=f_libalimc0>
>      > [2]
>     https://www.mail-archive.com/virtio-dev@lists.oasis-open.org/msg12665.html <https://www.mail-archive.com/virtio-dev@lists.oasis-open.org/msg12665.html>
>      > [3]
>     https://github.com/chromeos/virtio-media/blob/main/TRY_IT_OUT.md
>     <https://github.com/chromeos/virtio-media/blob/main/TRY_IT_OUT.md>
>      >
>      > Albert Esteve (1):
>      >    virtio-media: Add virtio media device specification
>      >
>      >   conformance.tex                           |  13 +-
>      >   content.tex                               |   1 +
>      >   device-types/media/description.tex        | 574
>     ++++++++++++++++++++++
>      >   device-types/media/device-conformance.tex |  11 +
>      >   device-types/media/driver-conformance.tex |   9 +
>      >   5 files changed, 604 insertions(+), 4 deletions(-)
>      >   create mode 100644 device-types/media/description.tex
>      >   create mode 100644 device-types/media/device-conformance.tex
>      >   create mode 100644 device-types/media/driver-conformance.tex
>      >
> 
>     Kind regards
> 
>     -- 
>     Alexander Gordeev
>     Senior Software Engineer
> 
>     OpenSynergy GmbH
>     Rotherstr. 20, 10245 Berlin
>     www.opensynergy.com <http://www.opensynergy.com>
> 

-- 
Alexander Gordeev
Senior Software Engineer

OpenSynergy GmbH
Rotherstr. 20, 10245 Berlin
www.opensynergy.com