Logging/Debugging ================= Weston's printf --------------- Logging in weston takes place through :func:`weston_log()` function, which calls a log handler (:var:`log_handler`) that has to be installed before actually calling :func:`weston_log()`. In weston, the log handler makes use of the logging framework which is (mostly) comprised of :ref:`log scopes` (produces of data) and :ref:`subscribers`. Logging context --------------- Management of the logging framework in weston happens under the :type:`weston_log_context` object and is entirely separated from the main compositor instance (:type:`weston_compositor`). The compositor instance can be brought up much more later, but in the same time logging can take place much earlier without the need of a compositor instance. Instantiation of the :type:`weston_log_context` object takes place using :func:`weston_log_ctx_compositor_create()` and clean-up/destroy with :func:`weston_log_ctx_compositor_destroy()`. Log scopes ---------- A scope represents a source for a data stream (i.e., a producer). You'll require one as a way to generate data. Creating a log scope is done using :func:`weston_compositor_add_log_scope()`. You can customize the scope behaviour and you'll require at least a name and a description for the scope. .. note:: A scope **name** identifies that scope. Scope retrieval from the :type:`weston_log_context` is done using the scope name. The name is important for the subscription part, detailed bit later. Log scopes are managed **explicitly**, and destroying the scope is done using :func:`weston_compositor_log_scope_destroy`. Available scopes in weston ~~~~~~~~~~~~~~~~~~~~~~~~~~ Weston has a few scopes worth mentioning: - **log** - a debug scope for generic logging, upon which :func:`weston_log` re-routes its data. - **proto** - debug scope that displays the protocol communication. It is similar to WAYLAND_DEBUG=server environmental variable but has the ability to distinguish multiple clients. - **scene-graph** - an one-shot debug scope which describes the current scene graph comprising of layers (containers of views), views (which represent a window), their surfaces, sub-surfaces, buffer type and format, both in :samp:`DRM_FOURCC` type and human-friendly form. - **drm-backend** - Weston uses DRM (Direct Rendering Manager) as one of its backends and this debug scope display information related to that: details the transitions of a view as it takes before being assigned to a hardware plane or to a renderer, current assignments of views, the compositing mode Weston is using for rendering the scene-graph, describes the current hardware plane properties like CRTC_ID, FB_ID, FORMAT when doing a commit or a page-flip. It incorporates the scene-graph scope as well. - **xwm-wm-x11** - a scope for the X11 window manager in Weston for supporting Xwayland, printing some X11 protocol actions. - **content-protection-debug** - scope for debugging HDCP issues. .. note:: Besides 'log' scope, which is a generic scope, intended for usage through :func:`weston_log`, all the others scopes listed above could suffer various modifications and might not represent a current list on which one should rely upon. Subscribers ----------- Besides creating a creating a scope, a subscriber (:type:`weston_log_subscriber`) object needs to be created. The subscriber object is an opaque object (private) and allows customization of the back-end side of libweston. The subscriber object can define its own methods. Users wanting to define a new data stream should extend this :type:`weston_log_subscriber`. For example libweston make uses of several type of subscribers, specific to the data streams they will be generating: - a **'logger'** type created by :func:`weston_log_subscriber_create_log()` - a **'flight-recoder'** type created by :func:`weston_log_subscriber_destroy_flight_rec()` - for the **'weston-debug'** protocol, which is private/hidden created whenever a client connects Like log scopes, the subscribers are also manged **explicitly** and both of the subscriber types above have their destroy counter-parts. `weston-debug` protocol is a bit special in this regard as the destroying part is handled implicitly using wayland protocol specifics. Once the subscriber has been created there needs to be a subscription process in which we establish a relationship between the subscriber and the scope. To create a subscription we use :func:`weston_log_subscribe` which uses the subscriber created previously and the scope name. If the scope was not created at the time, the subscription will be (at least for a time) a *pending subscription*. Once the scope is created the *pending subscription* is destroyed, not before creating a new subscription to accommodate the initial/original one. .. note:: The subscription process is (an) internal API and is managed implictly. When a scope is being destroyed the subscriptions for this scope will be destroyed as well. Logger ~~~~~~ weston uses a logger type of a subscriber for logging everyhing in the code (through the help of :func:`weston_log()`). The subscriber method (:func:`weston_log_subscriber_create_log()`) takes an :samp:`FILE *` as an argument in case the std :samp:`stdout` file-descriptor is not where the data should be sent to. Additionally, specifying which scopes to subscribe to can be done using :samp:`--logger-scopes` command line option. As log scopes are already created in the code, this merely subscribes to them. Default, the 'log' scope is being subscribr to the logger subscriber. Flight recorder ~~~~~~~~~~~~~~~ The flight recorder acts like a black box found in airplanes: it accumulates data until the user wants to display its contents. The backed up storage is a simple ring-buffer of a compiled-time fixed size value, and the memory is forcibly-mapped such that we make sure the kernel allocated storage for it. The user can use the debug keybinding :samp:`KEY_D` (shift+mod+space-d) to force the contents to be printed on :samp:`stdout` file-descriptor. The user has first to specify which log scope to subscribe to. Specifying which scopes to subscribe for the flight-recorder can be done using :samp:`--flight-rec-scopes`. By default, the 'log' scope and 'drm-backend' are the scopes subscribed to. weston-debug protocol ~~~~~~~~~~~~~~~~~~~~~ Weston-debug protocol is only present in the weston compositor (i.e., a weston specific compositor). It make uses of the the logging framework presented above, with the exception that the subscription happens automatically rather than manually with :func:`weston_log_subscribe()` in case of the other two types of subscribers. Also the subscriber is created once the client has connected and requested data from a log scope. This means that each time a client connects a new subscriber will be created. For each stream subscribed a subscription will be created. Enabling the debug-protocol happens using the :samp:`--debug` command line. .. doxygengroup:: debug-protocol :content-only: Weston Log API -------------- .. doxygengroup:: wlog :content-only: Logging API ----------- .. doxygengroup:: log :content-only: Internal logging API -------------------- .. note:: The following is mean to be internal API and aren't exposed in libweston! .. doxygengroup:: internal-log :content-only: