This adds a few lines describing `hub` aggregator configuration
for aggregation of several backend devices with a single frontend
device.
Signed-off-by: Roman Penyaev <r.peni...@gmail.com>
Cc: "Marc-André Lureau" <marcandre.lur...@redhat.com>
Cc: qemu-devel@nongnu.org
---
qemu-options.hx | 48 ++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 44 insertions(+), 4 deletions(-)
diff --git a/qemu-options.hx b/qemu-options.hx
index 7090d59f6f10..fdc46f7e68b3 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3720,7 +3720,7 @@ SRST
The general form of a character device option is:
``-chardev backend,id=id[,mux=on|off][,options]``
- Backend is one of: ``null``, ``socket``, ``udp``, ``msmouse``,
+ Backend is one of: ``null``, ``socket``, ``udp``, ``msmouse``, ``hub``,
``vc``, ``ringbuf``, ``file``, ``pipe``, ``console``, ``serial``,
``pty``, ``stdio``, ``braille``, ``parallel``,
``spicevmc``, ``spiceport``. The specific backend will determine the
@@ -3777,9 +3777,10 @@ The general form of a character device option is:
the QEMU monitor, and ``-nographic`` also multiplexes the console
and the monitor to stdio.
- There is currently no support for multiplexing in the other
- direction (where a single QEMU front end takes input and output from
- multiple chardevs).
+ If you need to aggregate data in the opposite direction (where one
+ QEMU frontend interface receives input and output from multiple
+ backend chardev devices), please refer to the paragraph below
+ regarding chardev ``hub`` aggregator device configuration.
Every backend supports the ``logfile`` option, which supplies the
path to a file to record all data transmitted via the backend. The
@@ -3879,6 +3880,45 @@ The available backends are:
Forward QEMU's emulated msmouse events to the guest. ``msmouse``
does not take any options.
+``-chardev hub,id=id,chardevs.0=id[,chardevs.N=id]`` Explicitly create
+ chardev backend hub device with the possibility to aggregate input
+ from multiple backend devices and forward it to a single frontend
+ device. Additionally, `hub` device takes the output from the
+ frontend device and sends it back to all the connected backend
+ devices. This allows for seamless interaction between different
+ backend devices and a single frontend interface. Aggregation
+ supported for up to 4 chardev devices. (Since 10.0)
+
+ For example, the following is a use case of 2 backend devices:
+ virtual console ``vc0`` and a pseudo TTY ``pty0`` connected to
+ a single virtio hvc console frontend device with a hub ``hub0``
+ help. Virtual console renders text to an image, which can be
+ shared over the VNC protocol. In turn, pty backend provides
+ bidirectional communication to the virtio hvc console over the
+ pseudo TTY file. The example configuration can be as follows:
+
+ ::
+
+ -chardev pty,path=/tmp/pty,id=pty0 \
+ -chardev vc,id=vc0 \
+ -chardev hub,id=hub0,chardevs.0=pty0,chardevs.1=vc0 \
+ -device virtconsole,chardev=hub0 \
+ -vnc 0.0.0.0:0
+
+ Once QEMU starts VNC client and any TTY emulator can be used to
+ control a single hvc console:
+
+ ::
+
+ # Start TTY emulator
+ tio /tmp/pty
+
+ # Start VNC client and switch to virtual console Ctrl-Alt-2
+ vncviewer :0
+
+ Several frontend devices is not supported. Stacking of multiplexers
+ and hub devices is not supported as well.
+
``-chardev vc,id=id[[,width=width][,height=height]][[,cols=cols][,rows=rows]]``
Connect to a QEMU text console. ``vc`` may optionally be given a
specific size.
--
2.43.0
