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qemu/include/chardev
Roman Penyaev b66ed23238 chardev/char-hub: implement backend chardev aggregator
This patch implements a new chardev backend `hub` device, which
aggregates input from multiple backend devices and forwards 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.

The idea of the change is trivial: keep list of backend devices
(up to 4), init them on demand and forward data buffer back and
forth.

The following is QEMU command line example:

   -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

Which creates 2 backend devices: text virtual console (`vc0`) and a
pseudo TTY (`pty0`) connected to the single virtio hvc console with
the backend aggregator (`hub0`) help. `vc0` renders text to an image,
which can be shared over the VNC protocol.  `pty0` is a pseudo TTY
backend which provides biderectional communication to the virtio hvc
console.

'chardevs.N' list syntax is used for the sake of compatibility with
the representation of JSON lists in 'key=val' pairs format of the
util/keyval.c, despite the fact that modern QAPI way of parsing,
namely qobject_input_visitor_new_str(), is not used. Choice of keeping
QAPI list syntax may help to smoothly switch to modern parsing in the
future.

Signed-off-by: Roman Penyaev <r.peniaev@gmail.com>
Reviewed-by: "Marc-André Lureau" <marcandre.lureau@redhat.com>
Cc: qemu-devel@nongnu.org
Message-ID: <20250123085327.965501-3-r.peniaev@gmail.com>
3 weeks ago
..
char-fd.h Use DECLARE_*CHECKER* macros 5 years ago
char-fe.h chardev/mux: convert size members to unsigned int 4 months ago
char-io.h Include qemu/main-loop.h less 6 years ago
char-parallel.h
char-serial.h
char-socket.h chardev: introduce 'reconnect-ms' and deprecate 'reconnect' 5 months ago
char-win-stdio.h
char-win.h Use DECLARE_*CHECKER* macros 5 years ago
char.h chardev/char-hub: implement backend chardev aggregator 3 weeks ago
spice.h chardev/spice: simplify chardev setup 4 years ago