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Cc: Eric Blake <eblake@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>,
Mahmoud Mandour <ma.mandourr@gmail.com>,
Markus Armbruster <armbru@redhat.com>, peter.maydell@linaro.org,
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=?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= <marcandre.lureau@redhat.com>,
Roman Penyaev <r.peniaev@gmail.com>
Subject: [PULL 4/8] qemu-options.hx: describe hub chardev and aggregation of
several backends
Date: Mon, 3 Feb 2025 16:57:16 +0400
Message-ID: <20250203125721.640451-5-marcandre.lureau@redhat.com>
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From: Roman Penyaev <r.peniaev@gmail.com>
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.peniaev@gmail.com>
Reviewed-by: "Marc-Andr=C3=A9 Lureau" <marcandre.lureau@redhat.com>
Cc: qemu-devel@nongnu.org
Message-ID: <20250123085327.965501-5-r.peniaev@gmail.com>
---
qemu-options.hx | 49 +++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 45 insertions(+), 4 deletions(-)
diff --git a/qemu-options.hx b/qemu-options.hx
index d19bf533d6..ec0090dfe2 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3733,7 +3733,7 @@ SRST
The general form of a character device option is:
=20
``-chardev backend,id=3Did[,mux=3Don|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
@@ -3790,9 +3790,10 @@ The general form of a character device option is:
the QEMU monitor, and ``-nographic`` also multiplexes the console
and the monitor to stdio.
=20
- 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.
=20
Every backend supports the ``logfile`` option, which supplies the
path to a file to record all data transmitted via the backend. The
@@ -3892,6 +3893,46 @@ The available backends are:
Forward QEMU's emulated msmouse events to the guest. ``msmouse``
does not take any options.
=20
+``-chardev hub,id=3Did,chardevs.0=3Did[,chardevs.N=3Did]``
+ 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=3D/tmp/pty,id=3Dpty0 \
+ -chardev vc,id=3Dvc0 \
+ -chardev hub,id=3Dhub0,chardevs.0=3Dpty0,chardevs.1=3Dvc0 \
+ -device virtconsole,chardev=3Dhub0 \
+ -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=3Did[[,width=3Dwidth][,height=3Dheight]][[,cols=3Dcols][,=
rows=3Drows]]``
Connect to a QEMU text console. ``vc`` may optionally be given a
specific size.
--=20
2.47.0