From fbc065fdc5013caced40ff2cbfb6a6d123ffc2db Mon Sep 17 00:00:00 2001 From: Marius Vlad Date: Mon, 14 Dec 2020 23:02:06 +0200 Subject: [PATCH] doc: Add running-weston.rst file Documentation file for explaning in more detail how to run weston, using launcher direct and specifying a non-default seat. This explains how to create a udev file and assign a particular GPU card to it, and potentially, other input devices. It also describes a bit additional arguments that can be passed on, as an introduction to using the DRM node for that particular seat. Fixes #460 Signed-off-by: Marius Vlad --- doc/sphinx/index.rst | 1 + doc/sphinx/toc/meson.build | 1 + doc/sphinx/toc/running-weston.rst | 168 ++++++++++++++++++++++++++++++ 3 files changed, 170 insertions(+) create mode 100644 doc/sphinx/toc/running-weston.rst diff --git a/doc/sphinx/index.rst b/doc/sphinx/index.rst index f952e645..8aa53b3e 100644 --- a/doc/sphinx/index.rst +++ b/doc/sphinx/index.rst @@ -5,6 +5,7 @@ Welcome to Weston documentation! :maxdepth: 2 :caption: Contents: + toc/running-weston.rst toc/libweston.rst toc/test-suite.rst toc/kiosk-shell.rst diff --git a/doc/sphinx/toc/meson.build b/doc/sphinx/toc/meson.build index f91e460d..b7190f78 100644 --- a/doc/sphinx/toc/meson.build +++ b/doc/sphinx/toc/meson.build @@ -1,6 +1,7 @@ # you need to add here any files you add to the toc directory as well files = [ 'kiosk-shell.rst', + 'running-weston.rst', 'libweston.rst', 'test-suite.rst', 'test-suite-api.rst', diff --git a/doc/sphinx/toc/running-weston.rst b/doc/sphinx/toc/running-weston.rst new file mode 100644 index 00000000..c8a24301 --- /dev/null +++ b/doc/sphinx/toc/running-weston.rst @@ -0,0 +1,168 @@ +Running Weston +============== + +libweston uses the concept of a *back-end* to abstract the interface to the +underlying environment where it runs on. Ultimately, the back-end is +responsible for handling the input and generate an output. Weston, as a +libweston user, can be run on different back-ends, including nested, by using +the wayland backend, but also on X11 or on a stand-alone back-end like +DRM/KMS and now deprecated fbdev. + +In most cases, people should allow Weston to choose the backend automatically +as it will produce the best results. That happens for instance when running +Weston on a machine that already has another graphical environment running, +being either another wayland compositor (e.g. Weston) or on a X11 server. +You should only specify the backend manually if you know that what Weston picks +is not the best, or the one you intended to use is different than the one +loaded. In that case, the backend can be selected by using ``-B [backend.so]`` +command line option. As each back-end uses a different way to get input and +produce output, it means that the most suitable back-end depends on the +environment being used. + +Available back-ends: + +* **drm** -- run stand-alone on DRM/KMS and evdev (recommend) + (`DRM kernel doc `_) +* **wayland** -- run as a Wayland application, nested in another Wayland compositor + instance +* **x11** -- run as a x11 application, nested in a X11 display server instance +* **rdp** -- run as an RDP server without local input or output +* **headless** -- run without input or output, useful for test suite +* **fbdev** -- run stand-alone on fbdev/evdev (deprecated) + +The job of gathering all the surfaces (windows) being displayed on an output and +stitching them together is performed by a *renderer*. By doing so, it is +compositing all surfaces into a single image, which is being handed out to a +back-end, and finally, displayed on the screen. + +libweston has a CPU-based type of renderer by making use of the +`Pixman `_ library, but also one that can make +use of the GPU to do that, which uses `OpenGL ES `_ +and it is simply called the GL-renderer. + +Most of the back-ends provide a command line option to disable the GL-renderer, +and use the CPU for doing that. That happens by appending to the command line +``--use-pixman`` when running Weston. One might use the CPU-based renderer +to exclude any other potential issues with the GL-renderer. + +Additional set-up steps +----------------------- + +Depending on your distribution some additional set-up parts might be required, +before actually launching Weston, although any fairly modern distribution +should have it already set-up for you. Weston creates its unix socket file (for +example, wayland-1) in the directory specified by the required +environment variable ``$XDG_RUNTIME_DIR``. Clients use the same variable to +find that socket. Normally this should already be provided by systemd. If you +are using a distribution that does not set-up ``$XDG_RUNTIME_DIR``, you +must set it using your shell profile capability. More info about how to +set-up that up, which depends to some extent on your shell, can be found at +`Building/Running Weston `_ + +Running Weston in a graphical environment +----------------------------------------- + +As stated previously, if you are already in a graphical environment, Weston +would infer and attempt to load up the correct back-end. Either running +in a Wayland compositor instance, or a X11 server, you should be able to run +Weston from a X terminal or a Wayland one. + +Running Weston on a stand-alone back-end +---------------------------------------- + +Now that we are aware of the concept of a back-end and a renderer, it is time to +introduce the concept of a seat, as stand-alone back-ends require one. A *seat* +is a collection of input devices like a keyboard and a mouse, and output +devices (monitors), forming the work or entertainment place for one person. It +could also include sound cards or cameras. A single computer could be serving +multiple seats. + +.. note:: + + A graphics card is **required** to be a part of the seat, as among + other things, it effectively drives the monitor. + +By default Weston will use the default seat named ``seat0``, but there's an +option to specify which seat Weston must use by passing ``--seat`` argument. + +You can start Weston from a VT, assuming that there's a `logind +`_ instance running +on the machine. If that's not available, you can use the ``weston-launch`` +application that can handle VT switching. + +Another way of launching Weston is via ssh or a serial terminal but is +currently a pain to do. One way is to run everything as root and issue +``weston --tty 2`` while TTY 2 is active for example. + +Running Weston on a different seat on a stand-alone back-end +------------------------------------------------------------ + +While Weston can be tested on top of an already running Wayland compositor or +an X11 server, another option might be to have an unused GPU card which can +be solely used by Weston. So, instead of having a dedicated machine to run +Weston for trying out the DRM-backend, by just having an extra GPU, one can +create a new seat that could access the unused GPU on the same machine (and +potentialy other inputs) and assign it to that seat. All of the +happening while you already have your graphical environment running. + +In order to have that set-up, the requirements/steps would be: + +* have an extra GPU card -- you could also use integrated GPUs, while your + other GPU is in use by another graphical environment +* create a udev file that assigns the card (and inputs) to another seat +* start Weston on that seat + +Start by creating a udev file, under ``/etc/udev/rules.d/`` adding something +similar to the following: + +:: + + ACTION=="remove", GOTO="id_insecure_seat_end" + + SUBSYSTEM=="drm", KERNEL=="card*", KERNELS=="0000:00:02.0", ENV{ID_SEAT}="seat-insecure" + + SUBSYSTEM=="input", ATTRS{idVendor}=="222a", ATTRS{idProduct}=="004d", OWNER="your_user_id", ENV{ID_SEAT}="seat-insecure", ENV{WL_OUTPUT}="HDMI-A-1" + SUBSYSTEM=="input", ATTRS{idVendor}=="03f0", ATTRS{idProduct}=="1198", OWNER="your_user_id", ENV{ID_SEAT}="seat-insecure" + + LABEL="id_insecure_seat_end" + +By using the above udev file, devices assigned to that particular seat +will be skipped by your normal display environment. Follow the naming scheme +when creating the file (``man 7 udev``). For instance you could use +``63-insecure-seat.rules`` as a filename, but take note that other udev rules +might also be present and could potentially affect the way in which they get +applied. Check that no other rules might take precedence before adding +this new one. + +.. warning:: + + This seat uses on purpose the name ``seat-insecure``, to warn users + that the input devices can be eavesdropped. Futher more, if you attempt + doing this on a VT, without being already in a graphical environment + (and although the udev rules do apply), there will be nothing stopping + the events from input devices reaching the virtual terminal. + +In the example above, there are two input devices, one of which is a +touch panel that is being assigned to a specific output (`HDMI-A-1`) and +another input which a mouse. Notice how ``ENV{ID_SEAT}`` and +``ENV{WL_OUTPUT}`` specify the name of the seat, respectively the input that +should be assign to a specific output. + +Resolving or extracting the udev key/value pair names, can be easily done with +the help of ``udevadm`` command, for instance issuing ``udevadm info -a +/dev/dri/cardX`` would give you the entire list of key values names for that +particular card. Archaically, one would might also use ``lsusb`` and ``lspci`` +commands to retrieve the PCI vendor and device codes associated with it. + +If there are no input devices the DRM-backend can be started by appending +``--continue-without-input`` or by editing ``weston.ini`` and adding to the +``core`` section ``require-input=false``. + +Then, weston can be run by selecting the DRM-backend and the seat ``seat-insecure``: + +:: + + ./weston -Bdrm-backend.so --seat=seat-insecure + +If everything went well you should see weston be up-and-running on an output +connected to that DRM device.