[libcamera-devel] [PATCH v3] Documentation: Add descriptions for env. variables
Sebastian Fricke
sebastian.fricke.linux at gmail.com
Wed Nov 4 19:48:48 CET 2020
Describe the environment variables used in libcamera, excluded
variables are `LIBCAMERA_IPA_FORCE_C_API` and `LIBCAMERA_IPA_PROXY_PATH`,
the former because it is likely to be removed and the later because
it has no current use-case.
Add a brief explanation for the IPA configuration and IPA modules.
List all the available Log levels and categories and add a short guide
for how to use them for debugging.
Signed-off-by: Sebastian Fricke <sebastian.fricke.linux at gmail.com>
---
Changes since V2:
* replace bullet point list with definition list
* Remove the category list as it is too difficult to maintain, instead
explain how the categories are set with the LOG_DECLARE_CATEGORY &
LOG_DEFINE_CATEGORY macros
* Remove the short summary for the IPA module, as it can be misleading
and probably not accurate enough
* Improve the notes for debugging part by linking to a full explaination
while extending the description in the documentation as well
* Add an example for the Log level setting
* Remove the documentation from guides and add it to the documentation
base path
Changes since V1:
* abandon the usage of tables as they are too clunky and difficult to
maintain
* Fix a wrong example that does not work on most distributions and setups
* Improve structure of log categories
---
Documentation/environment_variables.rst | 129 ++++++++++++++++++++++++
Documentation/index.rst | 1 +
Documentation/meson.build | 1 +
3 files changed, 131 insertions(+)
create mode 100644 Documentation/environment_variables.rst
diff --git a/Documentation/environment_variables.rst b/Documentation/environment_variables.rst
new file mode 100644
index 0000000..a03412b
--- /dev/null
+++ b/Documentation/environment_variables.rst
@@ -0,0 +1,129 @@
+Environment variables
+=====================
+
+List of variables
+-----------------
+
+LIBCAMERA_LOG_FILE
+ The custom destination for log output.
+
+ Example value: ``/home/{user}/camera_log.log``
+
+LIBCAMERA_LOG_LEVELS
+ Configure the verbosity of log messages for different categories (`more <#log-levels>`__)
+
+ Example value: ``*:DEBUG``
+
+LIBCAMERA_IPA_CONFIG_PATH
+ Define custom search locations for IPA configurations (`more <#ipa-configuration>`__)
+
+ Example value: ``/usr/path/one:/tmp/path/two``
+
+LIBCAMERA_IPA_MODULE_PATH
+ Define custom search locations for IPA modules (`more <#ipa-module>`__)
+
+ Example value: ``/usr/path/one:/tmp/path/two``
+
+Further details
+---------------
+
+Notes about debugging
+~~~~~~~~~~~~~~~~~~~~~
+
+The environment variables `LIBCAMERA_LOG_FILE` and `LIBCAMERA_LOG_LEVELS`
+are used to modify the destination and verbosity of messages provided by
+the libcamera API.
+
+The `LIBCAMERA_LOG_LEVELS` variable expects a comma-separated list of
+'category:level' pairs. The `level <#log-levels>`__ part can either be given
+as the index or the name in uppercase letters.
+While `category <#log-categories>`__ should either be the exact name of the
+category, the '*' wildcard symbol or no value, which targets every category.
+
+
+For more information refer to the `API-documentation <http://libcamera.org/api-html/log_8h.html#details>`__
+
+Examples:
+
+Enable full debug output to a separate file, for every `category <#log-categories>`__
+within a local environment:
+
+.. code:: bash
+
+ :~$ LIBCAMERA_LOG_FILE='/tmp/example_log.log' \
+ LIBCAMERA_LOG_LEVELS=0 \
+ cam --list
+
+Enable full debug output for the categories Camera & V4L2 within a
+global environment:
+
+.. code:: bash
+
+ :~$ export LIBCAMERA_LOG_LEVELS='Camera:DEBUG,V4L2:DEBUG'
+ :~$ cam --list
+
+Log levels
+~~~~~~~~~~~
+
+This is the list of available log levels, notice that all levels below
+the chosen one are printed, while those above are discarded.
+
+- DEBUG (0)
+- INFO (1)
+- WARN (2)
+- ERROR (3)
+- FATAL (4)
+
+Example:
+If you choose WARN (2), you will be able to see WARN (2), ERROR (3) & FATAL (4)
+but not DEBUG (0) & INFO (1).
+
+Log categories
+~~~~~~~~~~~~~~~
+
+Every category represent a specific area of the libcamera codebase,
+the names can be located within the source code, for example:
+`src/libcamera/camera_manager.cpp <https://git.libcamera.org/libcamera/libcamera.git/tree/src/libcamera/camera_manager.cpp#n35>`__
+
+.. code:: bash
+
+ LOG_DEFINE_CATEGORY(Camera)
+
+There are 2 available macros used to assign a category name to a part of the
+libcamera API:
+
+LOG_DEFINE_CATEGORY
+ This macro is required, in order to use the `LOGC` macro for a
+ particular category. It can only be used once for each category.
+ If you want to create log messages within multiple compilation
+ units for the same category utilize the `LOG_DECLARE_CATEGORY` macro,
+ in every file except the definition file.
+LOG_DECLARE_CATEGORY
+ Used for sharing an already defined category in between multiple
+ separately compiled files.
+
+Both macros have to be used within the namespace part of the C++ source code.
+
+
+IPA configuration
+~~~~~~~~~~~~~~~~~~
+
+The format and contents of the configuration file are specific to the
+IPA (Image Processing Algorithm). It usually contains data that optimize
+the behavior of the algorithms stored in JSON format. The
+`LIBCAMERA_IPA_CONFIG_PATH` variable can be used to specify custom
+storage locations to search for those configuration files.
+
+`Examples <https://git.libcamera.org/libcamera/libcamera.git/tree/src/ipa/raspberrypi/data>`__
+
+IPA module
+~~~~~~~~~~~
+
+In order to locate the correct IPA module for your hardware, libcamera gathers
+existing IPA modules from multiple locations. The default locations for this
+operation are the installed system path (for example on Debian:
+``/usr/local/x86_64-pc-linux-gnu/libcamera``) and the build directory.
+With the `LIBCAMERA_IPA_MODULE_PATH`, you can specify a non-default
+location to search for IPA modules.
+
+`Examples for existing IPA modules <https://git.libcamera.org/libcamera/libcamera.git/tree/src/ipa>`__
diff --git a/Documentation/index.rst b/Documentation/index.rst
index ff697d4..c49db18 100644
--- a/Documentation/index.rst
+++ b/Documentation/index.rst
@@ -17,3 +17,4 @@
Application Writer's Guide <guides/application-developer>
Pipeline Handler Writer's Guide <guides/pipeline-handler>
Tracing guide <guides/tracing>
+ Environment variables <environment_variables>
diff --git a/Documentation/meson.build b/Documentation/meson.build
index 26a12fc..8086abf 100644
--- a/Documentation/meson.build
+++ b/Documentation/meson.build
@@ -53,6 +53,7 @@ if sphinx.found()
'contributing.rst',
'docs.rst',
'index.rst',
+ 'environment_variables.rst',
'guides/introduction.rst',
'guides/application-developer.rst',
'guides/pipeline-handler.rst',
--
2.20.1
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