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[Qemu-devel] [PATCH] Add virtio input device specification.

From: Gerd Hoffmann
Subject: [Qemu-devel] [PATCH] Add virtio input device specification.
Date: Wed, 4 May 2016 14:38:44 +0200

Resuming the effort to get the input device specs actually merged.

Support has been added to the linux kernel version 4.1
and to qemu version 2.4.

git branch:

Rendered versions are available here:

Signed-off-by: Gerd Hoffmann <address@hidden>
 content.tex      |   2 +
 virtio-input.tex | 124 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 126 insertions(+)
 create mode 100644 virtio-input.tex

diff --git a/content.tex b/content.tex
index d989d98..4c0c4c9 100644
--- a/content.tex
+++ b/content.tex
@@ -5641,6 +5641,8 @@ descriptor for the \field{sense_len}, \field{residual},
 \field{status_qualifier}, \field{status}, \field{response} and
 \field{sense} fields.
 \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
 Currently there are three device-independent feature bits defined:
diff --git a/virtio-input.tex b/virtio-input.tex
new file mode 100644
index 0000000..cdc16ac
--- /dev/null
+++ b/virtio-input.tex
@@ -0,0 +1,124 @@
+\section{Input Device}\label{sec:Device Types / Input Device}
+The virtio input device can be used to create virtual human interface
+devices such as keyboards, mice and tablets.  It basically sends linux
+input layer events over virtio.
+in the linux source tree.
+\subsection{Device ID}\label{sec:Device Types / Input Device / Device ID}
+\subsection{Virtqueues}\label{sec:Device Types / Input Device / Virtqueues}
+\item[0] eventq
+\item[1] statusq
+\subsection{Feature bits}\label{sec:Device Types / Input Device / Feature bits}
+\subsection{Device configuration layout}\label{sec:Device Types / Input Device 
/ Device configuration layout}
+Device configuration holds all information the guest needs to handle
+the device, most importantly the events which are supported.
+enum virtio_input_config_select {
+       VIRTIO_INPUT_CFG_UNSET      = 0x00,
+       VIRTIO_INPUT_CFG_ID_NAME    = 0x01,
+       VIRTIO_INPUT_CFG_EV_BITS    = 0x11,
+       VIRTIO_INPUT_CFG_ABS_INFO   = 0x12,
+struct virtio_input_absinfo {
+       le32  min;
+       le32  max;
+       le32  fuzz;
+       le32  flat;
+struct virtio_input_config {
+       u8    select;
+       u8    subsel;
+       u8    size;
+       u8    reserved[5];
+       union {
+               char string[128];
+               u8   bitmap[128];
+               struct virtio_input_absinfo abs;
+       } u;
+To query a specific piece of information the driver MUST set
+\field{select} and \field{subsel} accordingly, then check \field{size}
+to see and how much information is available.  \field{size} can be
+zero if no information is available.
+\field{subsel} is not used and MUST be zero.
+Returns the name of the device, in \field{u.string}.
+Same as EVIOCGNAME ioctl for linux evdev devices.
+\field{subsel} is not used and MUST be zero.
+Returns the serial number of the device, in \field{u.string}.
+\field{subsel} is not used and MUST be zero.
+Returns input properties (INPUT_PROP_*) of the device, in \field{u.bitmap}.
+\field{subsel} specifies the event type (EV_*).  If \field{size} is
+non-zero the event type is supported and a bitmap the of supported
+event codes is returned in \field{u.bitmap}.
+Same as EVIOCGBIT ioctl.
+\field{subsel} specifies the absolute axes (ABS_*).
+Informations about the axis will be returned in \field{u.abs}.
+Same as EVIOCGABS ioctl.
+\subsection{Device Initialization}\label{sec:Device Types / Input Device / 
Device Initialization}
+\item The device is queried for supported event types and codes.
+\item The eventq is populated with receive buffers.
+\subsection{Device Operation}\label{sec:Device Types / Input Device / Device 
+\item Input events such as press and release events for keys and
+  buttons and motion events are send from the device to the driver
+  using the eventq.
+\item Status feedback such as keyboard led updates are sent from the
+  driver to the device using the statusq.
+\item Both queues use the same virtio_input_event struct.
+  \field{type}, \field{code} and \field{value} are filled according to
+  the linux input layer (evdev) interface, except that the fields are
+  in little endian byte order whereas the evdev ioctl interface uses
+  native endian.
+struct virtio_input_event {
+       le16 type;
+       le16 code;
+       le32 value;

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