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Unless required by applicable law or agreed to in writing, software
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See the License for the specific language governing permissions and
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Declaring elements
==================
.. _format_basics:
Element basics
--------------
Here is a rather complete example using the autotools element kind and git source kind:
.. code:: yaml
# Specify the kind of element this is
kind: autotools
# Specify some dependencies
depends:
- element1.bst
- element2.bst
# Specify the source which should be built
sources:
- kind: git
url: upstream:modulename.git
track: master
ref: d0b38561afb8122a3fc6bafc5a733ec502fcaed6
# Override some variables
variables:
sysconfdir: "%{prefix}/etc"
# Tweak the sandbox shell environment
environment:
LD_LIBRARY_PATH: /some/custom/path
# Specify the configuration of the element
config:
# Override autotools element default configure-commands
configure-commands:
- "%{configure} --enable-fancy-feature"
# Specify public domain data, visible to other elements.
public:
bst:
integration-commands:
- /usr/bin/update-fancy-feature-cache
# Specify a user id and group id to use in the build sandbox.
sandbox:
build-uid: 0
build-gid: 0
For most use cases you would not need to specify this much detail, we've provided
details here in order to have a more complete initial example.
Let's break down the above and give a brief explanation of what these attributes mean.
.. _format_element_names:
Element names and paths
~~~~~~~~~~~~~~~~~~~~~~~
An *element name* is the filename of an element relative to the project's
:ref:`element path <project_element_path>`.
Element names are the identifiers used to refer to elements, they are used
to specify an element's :ref:`dependencies <format_dependencies>`, to select
elements to build on the :ref:`command line <commands>`, and they are arbitrarily
used in various element specific configuration surfaces, for example the
*target* configuration of the :mod:`link <elements.link>` element is also
an *element name*.
Addressing elements
'''''''''''''''''''
When addressing elements in a single project, it is sufficient to use
the *element name* as a dependency or configuration parameter.
When muliple projects are connected through :mod:`junction <elements.junction>`
elements, there is a need to address elements which are not in the same
project but in a junctioned *subproject*. In the case that you need to
address elements across junction boundaries, one must use *element paths*.
An *element path* is a path to the element indicating the junction
elements leading up to the project, separated by ``:`` symbols, e.g.:
``junction.bst:element.bst``.
Elements can be address across multiple junction boundaries with multiple
``:`` separators, e.g.: ``junction.bst:junction.bst:element.bst``.
Element naming rules
''''''''''''''''''''
When naming the elements, use the following rules:
* The name of the file must have the ``.bst`` extension.
* All characters in the name must be printable 7-bit ASCII characters.
* Following characters are reserved and must not be part of the name:
- ``<`` (less than)
- ``>`` (greater than)
- ``:`` (colon)
- ``"`` (double quote)
- ``/`` (forward slash)
- ``\`` (backslash)
- ``|`` (vertical bar)
- ``?`` (question mark)
- ``*`` (asterisk)
Kind
~~~~
.. code:: yaml
# Specify the kind of element this is
kind: autotools
The ``kind`` attribute specifies which plugin will be operating on the element's input to
produce its output. Plugins define element types and each of them can be referred to by
name with the ``kind`` attribute.
To refer to a third party plugin, prefix the plugin with its package, for example:
.. code:: yaml
kind: buildstream-plugins:dpkg_build
.. _format_depends:
Depends
~~~~~~~
.. code:: yaml
# Specify some dependencies
depends:
- element1.bst
- element2.bst
Relationships between elements are specified with the ``depends`` attribute. Elements
may depend on other elements by specifying the :ref:`element names <format_element_names>`
they depend on here.
See :ref:`format_dependencies` for more information on the dependency model.
.. _format_build_depends:
Build-Depends
~~~~~~~~~~~~~
.. code:: yaml
# Specify some build-dependencies
build-depends:
- element1.bst
- element2.bst
Build dependencies between elements can be specified with the ``build-depends`` attribute.
The above code snippet is equivalent to:
.. code:: yaml
# Specify some build-dependencies
depends:
- filename: element1.bst
type: build
- filename: element2.bst
type: build
See :ref:`format_dependencies` for more information on the dependency model.
.. _format_runtime_depends:
Runtime-Depends
~~~~~~~~~~~~~~~
.. code:: yaml
# Specify some runtime-dependencies
runtime-depends:
- element1.bst
- element2.bst
Runtime dependencies between elements can be specified with the ``runtime-depends`` attribute.
The above code snippet is equivalent to:
.. code:: yaml
# Specify some runtime-dependencies
depends:
- filename: element1.bst
type: runtime
- filename: element2.bst
type: runtime
See :ref:`format_dependencies` for more information on the dependency model.
.. _format_sources:
Sources
~~~~~~~
.. code:: yaml
# Specify the source which should be built
sources:
- kind: git
url: upstream:modulename.git
track: master
ref: d0b38561afb8122a3fc6bafc5a733ec502fcaed6
Here we specify some input for the element, any number of sources may be specified.
By default the sources will be staged in the root of the element's build directory
in the build sandbox, but sources may specify a ``directory`` attribute to control
where the sources will be staged. The ``directory`` attribute may specify a build
sandbox relative subdirectory.
For example, one might encounter a component which requires a separate data package
in order to build itself, in this case the sources might be listed as:
.. code:: yaml
sources:
# Specify the source which should be built
- kind: git
url: upstream:modulename.git
track: master
ref: d0b38561afb8122a3fc6bafc5a733ec502fcaed6
# Specify the data package we need for build frobnication,
# we need it to be unpacked in a src/frobdir
- kind: tarball
directory: src/frobdir
url: data:frobs.tgz
ref: 9d4b1147f8cf244b0002ba74bfb0b8dfb3...
Like Elements, Source types are plugins which are indicated by the ``kind`` attribute.
Asides from the common ``kind`` and ``directory`` attributes which may be applied to all
Sources, refer to the Source specific documentation for meaningful attributes for the
particular Source.
Variables
~~~~~~~~~
.. code:: yaml
# Override some variables
variables:
sysconfdir: "%{prefix}/etc"
Variables can be declared or overridden from an element. Variables can also be
declared and overridden in the :ref:`projectconf`
See :ref:`format_variables` below for a more in depth discussion on variables in BuildStream.
.. _format_environment:
Environment
~~~~~~~~~~~
.. code:: yaml
# Tweak the sandbox shell environment
environment:
LD_LIBRARY_PATH: /some/custom/path
Environment variables can be set to literal values here, these environment
variables will be effective in the :mod:`Sandbox <buildstream.sandbox>` where
build instructions are run for this element.
Environment variables can also be declared and overridden in the :ref:`projectconf`
.. _format_config:
Config
~~~~~~
.. code:: yaml
# Specify the configuration of the element
config:
# Override autotools element default configure-commands
configure-commands:
- "%{configure} --enable-fancy-feature"
Here we configure the element itself. The autotools element provides sane defaults for
building sources which use autotools. Element default configurations can be overridden
in the ``project.conf`` file and additionally overridden in the declaration of an element.
For meaningful documentation on what can be specified in the ``config`` section for a given
element ``kind``, refer to the :ref:`element specific documentation <plugins>`.
.. _format_public:
Public
~~~~~~
.. code:: yaml
# Specify public domain data, visible to other elements.
public:
bst:
integration-commands:
- /usr/bin/update-fancy-feature-cache
Metadata declared in the ``public`` section of an element is visible to
any other element which depends on the declaring element in a given pipeline.
BuildStream itself consumes public data from the ``bst`` domain. The ``integration-commands``
demonstrated above for example, describe commands which should be run in an
environment where the given element is installed but before anything should be run.
An element is allowed to read domain data from any element it depends on, and users
may specify additional domains to be understood and processed by their own element
plugins.
The public data keys which are recognized under the ``bst`` domain
can be viewed in detail in the :ref:`builtin public data <public_builtin>` section.
.. _format_sandbox:
Sandbox
~~~~~~~
Configuration for the build sandbox (other than :ref:`environment variables <format_environment>`)
can be placed in the ``sandbox`` configuration. The UID and GID used by the user
in the group can be specified, as well as the desired OS and machine
architecture. Possible machine architecture follow the same list as specified in
the :ref:`architecture option <project_options_arch>`.
.. code:: yaml
# Specify a user id and group id to use in the build sandbox.
sandbox:
build-uid: 1003
build-gid: 1001
BuildStream normally uses uid 0 and gid 0 (root) to perform all
builds. However, the behaviour of certain tools depends on user id,
behaving differently when run as non-root. To support those builds,
you can supply a different uid or gid for the sandbox. Only
bwrap-style sandboxes support custom user IDs at the moment, and hence
this will only work on Linux host platforms.
.. code:: yaml
# Specify build OS and architecture
sandbox:
build-os: AIX
build-arch: power-isa-be
When building locally, if these don't match the host machine then generally the
build will fail. The exception is when the OS is Linux and the architecture
specifies an ``x86-32`` build on an ``x86-64`` machine, or ``aarch32`` build on
a ``aarch64`` machine, in which case the ``linux32`` command is prepended to the
bubblewrap command.
When building remotely, the OS and architecture are added to the ``Platform``
field in the ``Command`` uploaded. Whether this actually results in a building
the element for the desired OS and architecture is dependent on the server
having implemented these options the same as buildstream.
.. _format_dependencies:
Dependencies
------------
The dependency model in BuildStream is simplified by treating software distribution
and software building as separate problem spaces. This is to say that one element
can only ever depend on another element but never on a subset of the product which
another element produces.
In this section we'll quickly go over the few features BuildStream offers in its
dependency model.
Expressing dependencies
~~~~~~~~~~~~~~~~~~~~~~~
Dependencies in BuildStream are parameterizable objects, however as demonstrated
in the :ref:`above example <format_depends>`, they can also be expressed as simple
strings as a convenience shorthand in most cases, whenever the default dependency
attributes are suitable.
.. note::
Note the order in which element dependencies are declared in the ``depends``,
``build-depends`` and ``runtime-depends`` lists are not meaningful.
Dependency dictionary:
.. code:: yaml
# Fully specified dependency
depends:
- filename: foo.bst
type: build
junction: baseproject.bst
strict: false
Attributes:
* ``filename``
The :ref:`element name <format_element_names>` to depend on, or a list of mutiple element names.
Specifying multiple element names in a single dependency will result in multiple dependencies
being declared with common properties.
For example, one can declare multiple build dependencies with the same junction:
.. code:: yaml
# Declare three build dependencies from subproject.bst
depends:
- type: build
junction: subproject.bst
filename:
- element-a.bst
- element-b.bst
- element-c.bst
* ``junction``
This attribute can be used to specify the junction portion of the :ref:`element name <format_element_names>`
separately from the project local element name.
This should be the *element name* of the :mod:`junction <elements.junction>` element
in the local project, possibly followed by other junctions in subprojects leading
to the project in which the element you want to depend on resides.
In the case that a *junction* is specified, the ``filename`` attribute indicates an
element in the *junctioned project*.
* ``type``
This attribute is used to express the :ref:`dependency type <format_dependencies_types>`.
This field is not permitted in the :ref:`build-depends <format_build_depends>` or
:ref:`runtime-depends <format_runtime_depends>` lists.
* ``strict``
This attribute can be used to specify that this element should
be rebuilt when the dependency changes, even when
:ref:`strict mode <user_config_strict_mode>` has been turned off.
This is appropriate whenever a dependency's output is consumed
verbatim in the output of the depending element, for instance
when static linking is in use.
* ``config``
This attribute defines the custom :term:`dependency configuration <Dependency configuration>`,
which is supported by select :mod:`Element <buildstream.element>` implementations.
Elements which support :term:`dependency configuration <Dependency configuration>` do so
by implementing the
:func:`Element.configure_dependencies() <buildstream.element.Element.configure_dependencies>`
abstract method. It is up to each element or abstract element class to
document what is supported in their :term:`dependency configuration <Dependency configuration>`.
.. attention::
It is illegal to declare :term:`dependency configuration <Dependency configuration>`
on runtime dependencies, since runtime dependencies are not visible to the depending
element.
Redundant dependency declarations
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It is permitted to declare dependencies multiple times on the same element in the same
element declaration, the result will be an inclusive OR of all configurations you have
expressed in the redundant dependencies on the same element.
* If a dependency is defined once as a ``build`` dependency and once as a ``runtime``
:ref:`dependency type <format_dependencies_types>`, then the resulting dependency
type will be ``all``
* If any of the redundantly declared dependencies are specified as ``strict``, then
the resulting dependency will be ``strict``.
Declaring redundant dependencies on the same element can be interesting when you
need to specify multiple :term:`dependency configurations <Dependency configuration>`
for the same element. For example, one might want to stage the same dependency
in multiple locations in the build sandbox.
Cross-junction dependencies
~~~~~~~~~~~~~~~~~~~~~~~~~~~
As explained in the :ref:`element name <format_element_names>` section
on element addressing, elements can be addressed across junction boundaries
using *element paths* such as ``junction.bst:element.bst``. An element
at any depth can be specified by specifying multiple junction elements.
For example, one can specify a subproject element dependency with
the following syntax:
.. code:: yaml
build-depends:
- baseproject.bst:element.bst
And one can specify an element residing in a sub-subproject as a
dependency like so:
.. code:: yaml
depends:
- baseproject.bst:middleproject.bst:element.bst
.. _format_dependencies_types:
Dependency types
~~~~~~~~~~~~~~~~
The dependency ``type`` attribute defines what the dependency is required for
and is essential to how BuildStream plots a build plan.
There are three types which one can specify for a dependency:
* ``build``
A ``build`` dependency type states that the given element's product must
be staged in order to build the depending element. Depending on an element
which has ``build`` dependencies will not implicitly depend on that element's
``build`` dependencies.
For convenience, these can be specified under the :ref:`build-depends <format_build_depends>`
list.
* ``runtime``
A ``runtime`` dependency type states that the given element's product
must be present for the depending element to function. An element's
``runtime`` dependencies are not available to the element at build time.
For convenience, these can be specified under the :ref:`runtime-depends <format_runtime_depends>`
list.
* ``all``
An ``all`` dependency is the default dependency type. If ``all`` is specified,
or if ``type`` is not specified at all, then it is assumed that the dependency
is required both at build time and runtime.
.. note::
It is assumed that a dependency which is required for building an
element must run while building the depending element. This means that
``build`` depending on a given element implies that that element's
``runtime`` dependencies will also be staged for the purpose of building.
.. _format_variables:
Using variables
---------------
Variables in BuildStream are a way to make your build instructions and
element configurations more dynamic.
Referring to variables
~~~~~~~~~~~~~~~~~~~~~~
Variables are expressed as ``%{...}``, where ``...`` must contain only
alphanumeric characters and the separators ``_`` and ``-``. Further, the
first letter of ``...`` must be an alphabetic character.
.. code:: yaml
This is release version %{version}
Declaring and overriding variables
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
To declare or override a variable, one need only specify a value
in the relevant *variables* section:
.. code:: yaml
variables:
hello: Hello World
You can refer to another variable while declaring a variable:
.. code:: yaml
variables:
release-text: This is release version %{version}
The order in which you declare variables is arbitrary, so long as there is no cyclic
dependency and that all referenced variables are declared, the following is fine:
.. code:: yaml
variables:
release-text: This is release version %{version}
version: 5.5
.. note::
It should be noted that variable resolution only happens after all
:ref:`Element Composition <format_composition>` has already taken place.
This is to say that overriding ``%{version}`` at a higher priority will affect
the final result of ``%{release-text}``.
**Example:**
.. code:: yaml
kind: autotools
# Declare variable, expect %{version} was already declared
variables:
release-text: This is release version %{version}
config:
# Customize the installation
install-commands:
- |
%{make-install} RELEASE_TEXT="%{release-text}"
Variables declared by BuildStream
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
BuildStream declares a set of :ref:`builtin <project_builtin_defaults>`
variables that may be overridden. In addition, the following
read-only variables are also dynamically declared by BuildStream:
* ``element-name``
The name of the element being processed (e.g base/alpine.bst).
* ``project-name``
The name of project where BuildStream is being used.
* ``project-root`` & ``project-root-uri``
The directory where the project is located on the host.
This variable is only available when declaring
:ref:`source alias values <project_source_aliases>` or
:ref:`source mirror values <project_essentials_mirrors>` and allows
access to files in a project on the build host.
* The ``project-root`` variable is a regular absolute path
* The ``project-root-uri`` variable is a properly quoted ``file://`` URI
.. tip::
Use this variable to declare :ref:`source alias values <project_source_aliases>`
to refer to files which you store as a part of your project, e.g. tarballs
which you have committed to you BuildStream project.
.. attention::
This feature has been provided for convenience when putting together a
project without the use of proper infrastructure.
A better long term solution for accessing internal binaries and source
code is to setup internal infrastructure in your organization and use
the regular ways to access these sources from a well known internal URI.
* ``toplevel-root`` & ``toplevel-root-uri``
The directory where the toplevel project is located on the host.
This variable is only available when declaring
:ref:`source alias values <project_source_aliases>` or
:ref:`source mirror values <project_essentials_mirrors>` and allows
access to files in a project on the build host.
* The ``toplevel-root`` variable is a regular absolute path
* The ``toplevel-root-uri`` variable is a properly quoted ``file://`` URI
.. tip::
Use this variable to declare :ref:`source alias values <project_source_aliases>`
to refer to files which you do not store as a part of your project, e.g.
tarballs or git repositories which must be placed in a directory within
the toplevel project before running the build.
.. attention::
This feature has been provided for convenience when putting together a
project without the use of proper infrastructure.
A better long term solution for accessing internal binaries and source
code is to setup internal infrastructure in your organization and use
the regular ways to access these sources from a well known internal URI.
* ``max-jobs``
Maximum number of parallel build processes within a given
build, support for this is conditional on the element type
and the build system used (any element using 'make' can
implement this).