| Message ID | 20241009174517.286935-1-r.peniaev@gmail.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | chardev: implement backend chardev multiplexing | expand |
Hi Roman On Wed, Oct 9, 2024 at 9:47 PM Roman Penyaev <r.peniaev@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.peniaev@gmail.com> > Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com> > Cc: qemu-devel@nongnu.org > > -- > 2.43.0 > > >
Hi Marc-André, On Wed, Oct 9, 2024 at 8:23 PM Marc-André Lureau <marcandre.lureau@gmail.com> wrote: [cut] > > > Please rebase, it fails to apply cleanly on master. Yep. > > 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. I can give it a try. Let's see how it goes. -- Roman > > 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.peniaev@gmail.com> >> Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com> >> Cc: qemu-devel@nongnu.org >> >> -- >> 2.43.0 >> >> > > > -- > Marc-André Lureau
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 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.peniaev@gmail.com> Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com> Cc: qemu-devel@nongnu.org