[PATCH v4 3/3] docs: Add documentation for vhost based RNG implementation

[Mathieu Poirier]

Add description and example for the vhost-user based RNG implementation.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
---
 docs/system/devices/vhost-user-rng.rst | 39 ++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)
 create mode 100644 docs/system/devices/vhost-user-rng.rst

diff --git a/docs/system/devices/vhost-user-rng.rst 
b/docs/system/devices/vhost-user-rng.rst
new file mode 100644
index 000000000000..a145d4105c1a
--- /dev/null
+++ b/docs/system/devices/vhost-user-rng.rst
@@ -0,0 +1,39 @@
+QEMU vhost-user-rng - RNG emulation
+===================================
+
+Background
+----------
+
+What follows builds on the material presented in vhost-user.rst - it should
+be reviewed before moving forward with the content in this file.
+
+Description
+-----------
+
+The vhost-user-rng device implementation was designed to work with a random
+number generator daemon such as the one found in the vhost-device crate of
+the rust-vmm project available on github [1].
+
+[1]. https://github.com/rust-vmm/vhost-device
+
+Examples
+--------
+
+The daemon should be started first:
+
+::
+
+  host# vhost-device-rng --socket-path=rng.sock -c 1 -m 512 -p 1000
+
+The QEMU invocation needs to create a chardev socket the device can
+use to communicate as well as share the guests memory over a memfd.
+
+::
+
+  host# qemu-system                                                            
\
+      -chardev socket,path=$(PATH)/rng.sock,id=rng0                            
\
+      -device vhost-user-rng-pci,chardev=rng0                                  
\
+      -m 4096                                                                  
\
+      -object memory-backend-file,id=mem,size=4G,mem-path=/dev/shm,share=on    
\
+      -numa node,memdev=mem                                                    
\
+      ...
-- 
2.25.1