[PATCH v1 2/4] docs/system: Add vhost-user-input documentation

[Leo Yan <leo.yan@linaro.org>]

This adds basic documentation for vhost-user-input.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
---
 docs/system/devices/vhost-user-input.rst | 44 ++++++++++++++++++++++++
 docs/system/devices/vhost-user.rst       |  2 +-
 2 files changed, 45 insertions(+), 1 deletion(-)
 create mode 100644 docs/system/devices/vhost-user-input.rst

diff --git a/docs/system/devices/vhost-user-input.rst b/docs/system/devices/vhost-user-input.rst
new file mode 100644
index 0000000000..601282e658
--- /dev/null
+++ b/docs/system/devices/vhost-user-input.rst
@@ -0,0 +1,44 @@
+.. _vhost_user_rng:
+
+QEMU vhost-user-input - Input emulation
+=======================================
+
+This document describes the setup and usage of the Virtio input device.
+The Virtio input device is a paravirtualized device for input events.
+
+Description
+-----------
+
+The vhost-user-input device implementation was designed to work with a daemon
+polling on input devices and passes input events to the guest.
+
+QEMU provides a backend implementation in contrib/vhost-user-input.
+
+Linux kernel support
+--------------------
+
+Virtio input requires a guest Linux kernel built with the
+``CONFIG_VIRTIO_INPUT`` option.
+
+Examples
+--------
+
+The backend daemon should be started first:
+
+::
+
+  host# vhost-user-input --socket-path=input.sock	\
+      --evdev-path=/dev/input/event17
+
+The QEMU invocation needs to create a chardev socket to communicate with the
+backend daemon and share memory with the guest over a memfd.
+
+::
+
+  host# qemu-system								\
+      -chardev socket,path=/tmp/input.sock,id=mouse0				\
+      -device vhost-user-input-pci,chardev=mouse0				\
+      -m 4096 									\
+      -object memory-backend-file,id=mem,size=4G,mem-path=/dev/shm,share=on	\
+      -numa node,memdev=mem							\
+      ...
diff --git a/docs/system/devices/vhost-user.rst b/docs/system/devices/vhost-user.rst
index c6afc4836f..75b40f08c6 100644
--- a/docs/system/devices/vhost-user.rst
+++ b/docs/system/devices/vhost-user.rst
@@ -42,7 +42,7 @@ platform details for what sort of virtio bus to use.
     - See https://github.com/rust-vmm/vhost-device
   * - vhost-user-input
     - Generic input driver
-    - See contrib/vhost-user-input
+    - :ref:`vhost_user_input`
   * - vhost-user-rng
     - Entropy driver
     - :ref:`vhost_user_rng`
-- 
2.34.1