Hi Roman On Wed, Oct 9, 2024 at 9:47 PM Roman Penyaev <r.peni...@gmail.com> wrote:
> Mux is a character backend (host side) device, which multiplexes > multiple frontends with one backend device. The following is a > few lines from the QEMU manpage [1]: > > A multiplexer is a "1:N" device, and here the "1" end is your > specified chardev backend, and the "N" end is the various parts > of QEMU that can talk to a chardev. > > But sadly multiple backends are not supported. > > This work implements multiplexing capability of several backend > devices, which opens up an opportunity to use a single frontend > device on the guest, which can be manipulated from several > backend devices. > > The motivation is the EVE project [2], where it would be very > convenient to have a virtio console frontend device on the guest that > can be controlled from multiple backend devices. The following is > an example of the QEMU command line: > > -chardev mux-be,id=mux0 \ > -chardev > socket,path=/tmp/sock,server=on,wait=off,id=sock0,mux-be-id=mux0 \ > -chardev vc,id=vc0,mux-be-id=mux0 \ > -device virtconsole,chardev=mux0 \ > -vnc 0.0.0.0:0 > > Which creates 2 backend devices: text virtual console (`vc0`) and a > socket (`sock0`) connected to the single virtio hvc console with the > backend multiplexer (`mux0`) help. `vc0` renders text to an image, > which can be shared over the VNC protocol. `sock0` is a socket > backend which provides biderectional communication to the virtio hvc > console. > > New type of multiplexer `mux-be` actually is an alias for the same > `MuxChardev` struct, which uses same functions as for the original > `mux` type, but supports multiplexing N backends with 1 frontend. > > Once QEMU starts VNC client and any TTY emulator can be used to > control a single hvc console, for example these two different > consoles should have similar input and output due the buffer > multiplexing: > > # VNC client > vncviewer :0 > > # TTY emulator > socat unix-connect:/tmp/sock pty,link=/tmp/pty > tio /tmp/pty > > Difference to the previous version: > > * Separate type for the backend multiplexer `mux-be` > * Handle EAGAIN on write to the backend device > * Support of watch of previously failed backend device > * Proper json support of the `mux-be-id` option > * Unit test for the `mux-be` multiplexer > > [1] https://www.qemu.org/docs/master/system/qemu-manpage.html#hxtool-6 > [2] https://github.com/lf-edge/eve > > Roman Penyaev (5): > chardev/char: introduce `mux-be-id=ID` option and _MUX_BE type > chardev/char: rename `mux_cnt` to `fe_cnt` for the `MuxChardev` > chardev/char-mux: implement backend chardev multiplexing > tests/unit/test-char: add unit test for the `mux-be` multiplexer > qemu-options.hx: describe multiplexing of several backend devices > Please rebase, it fails to apply cleanly on master. Can you try to split MuxChardev in a base common class? You could have MuxBase or simply Mux abstract, with MuxFe (for 'mux') & MuxBe (for 'mux-be'). This should clarify the code a bit and avoid sharing the same struct with unused fields. Thanks for the tests, that helps a lot! > chardev/char-fe.c | 14 ++- > chardev/char-mux.c | 212 +++++++++++++++++++++++++++++++----- > chardev/char.c | 57 ++++++++-- > chardev/chardev-internal.h | 33 +++++- > include/chardev/char.h | 1 + > qapi/char.json | 9 +- > qemu-options.hx | 46 +++++++- > tests/unit/test-char.c | 217 ++++++++++++++++++++++++++++++++++++- > 8 files changed, 538 insertions(+), 51 deletions(-) > > Signed-off-by: Roman Penyaev <r.peni...@gmail.com> > Cc: "Marc-André Lureau" <marcandre.lur...@redhat.com> > Cc: qemu-devel@nongnu.org > > -- > 2.43.0 > > > -- Marc-André Lureau
