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// -*- mode:doc; -*-
Package directory
~~~~~~~~~~~~~~~~~
First of all, create a directory under the +package+ directory for
your software, for example +libfoo+.
Some packages have been grouped by topic in a sub-directory:
+multimedia+, +java+, +x11r7+, and +games+. If your package fits in
one of these categories, then create your package directory in these.
+Config.in+ file
^^^^^^^^^^^^^^^^
Then, create a file named +Config.in+. This file will contain the
option descriptions related to our +libfoo+ software that will be used
and displayed in the configuration tool. It should basically contain:
---------------------------
config BR2_PACKAGE_LIBFOO
bool "libfoo"
help
This is a comment that explains what libfoo is.
http://foosoftware.org/libfoo/
---------------------------
The +bool+ line, +help+ line and other meta-informations about the
configuration option must be indented with one tab. The help text
itself should be indented with one tab and two spaces, and it must
mention the upstream URL of the project.
Of course, you can add other sub-options into a +if
BR2_PACKAGE_LIBFOO...endif+ statement to configure particular things
in your software. You can look at examples in other packages. The
syntax of the +Config.in+ file is the same as the one for the kernel
Kconfig file. The documentation for this syntax is available at
http://lxr.free-electrons.com/source/Documentation/kbuild/kconfig-language.txt[]
Finally you have to add your new +libfoo/Config.in+ to
+package/Config.in+ (or in a category subdirectory if you decided to
put your package in one of the existing categories). The files
included there are 'sorted alphabetically' per category and are 'NOT'
supposed to contain anything but the 'bare' name of the package.
--------------------------
source "package/libfoo/Config.in"
--------------------------
[[depends-on-vs-select]]
The +Config.in+ file of your package must also ensure that
dependencies are enabled. Typically, Buildroot uses the following
rules:
* Use a +select+ type of dependency for dependencies on
libraries. These dependencies are generally not obvious and it
therefore make sense to have the kconfig system ensure that the
dependencies are selected. For example, the _libgtk2_ package uses
+select BR2_PACKAGE_LIBGLIB2+ to make sure this library is also
enabled.
The +select+ keyword express the dependency with a backward
semantic.
* Use a +depends on+ type of dependency when the user really needs to
be aware of the dependency. Typically, Buildroot uses this type of
dependency for dependencies on toolchain options (target
architecture, MMU support, C library, C++ support, large file
support, thread support, RPC support, IPV6 support, WCHAR support),
or for dependencies on "big" things, such as the X.org system. In
some cases, especially dependency on toolchain options, it is
recommended to add a +comment+ displayed when the option is not
enabled, so that the user knows why the package is not available.
The +depends on+ keyword express the dependency with a forward
semantic.
.Note
The current problem with the _kconfig_ language is that these two
dependency semantics are not internally linked. Therefore, it may be
possible to select a package, whom one of its dependencies/requirement
is not met.
An example illustrates both the usage of +select+ and +depends on+.
--------------------------
config BR2_PACKAGE_ACL
bool "acl"
select BR2_PACKAGE_ATTR
depends on BR2_LARGEFILE
help
POSIX Access Control Lists, which are used to define more
fine-grained discretionary access rights for files and
directories.
This package also provides libacl.
http://savannah.nongnu.org/projects/acl
comment "acl requires a toolchain with LARGEFILE support"
depends on !BR2_LARGEFILE
--------------------------
Note that these two dependency types are only transitive with the
dependencies of the same kind.
This means, in the following example:
--------------------------
config BR2_PACKAGE_A
bool "Package A"
config BR2_PACKAGE_B
bool "Package B"
depends on BR2_PACKAGE_A
config BR2_PACKAGE_C
bool "Package C"
depends on BR2_PACKAGE_B
config BR2_PACKAGE_D
bool "Package D"
select BR2_PACKAGE_B
config BR2_PACKAGE_E
bool "Package E"
select BR2_PACKAGE_D
--------------------------
* Selecting +Package C+ will be visible if +Package B+ has been
selected, which in turn is only visible if +Package A+ has been
selected.
* Selecting +Package E+ will select +Package D+, which will select
+Package B+, it will not check for the dependencies of +Package B+,
so it will not select +Package A+.
* Since +Package B+ is selected but +Package A+ is not, this violates
the dependency of +Package B+ on +Package A+. Therefore, in such a
situation, the transitive dependency has to be added explicitly:
--------------------------
config BR2_PACKAGE_D
bool "Package D"
select BR2_PACKAGE_B
depends on BR2_PACKAGE_A
config BR2_PACKAGE_E
bool "Package E"
select BR2_PACKAGE_D
depends on BR2_PACKAGE_A
--------------------------
Overall, for package library dependencies, +select+ should be
preferred.
Note that such dependencies will make sure that the dependency option
is also enabled, but not necessarily built before your package. To do
so, the dependency also needs to be expressed in the +.mk+ file of the
package.
Further formating details: see xref:writing-rules-config-in[the
writing rules].
The +.mk+ file
^^^^^^^^^^^^^^
Finally, here's the hardest part. Create a file named +libfoo.mk+. It
describes how the package should be downloaded, configured, built,
installed, etc.
Depending on the package type, the +.mk+ file must be written in a
different way, using different infrastructures:
* *Makefiles for generic packages* (not using autotools or CMake):
These are based on an infrastructure similar to the one used for
autotools-based packages, but requires a little more work from the
developer. They specify what should be done for the configuration,
compilation, installation and cleanup of the package. This
infrastructure must be used for all packages that do not use the
autotools as their build system. In the future, other specialized
infrastructures might be written for other build systems. We cover
them through in a xref:generic-package-tutorial[tutorial] and a
xref:generic-package-reference[reference].
* *Makefiles for autotools-based software* (autoconf, automake, etc.):
We provide a dedicated infrastructure for such packages, since
autotools is a very common build system. This infrastructure 'must'
be used for new packages that rely on the autotools as their build
system. We cover them through a xref:autotools-package-tutorial[tutorial]
and xref:autotools-package-reference[reference].
* *Makefiles for cmake-based software*: We provide a dedicated
infrastructure for such packages, as CMake is a more and more
commonly used build system and has a standardized behaviour. This
infrastructure 'must' be used for new packages that rely on
CMake. We cover them through a xref:cmake-package-tutorial[tutorial]
and xref:cmake-package-reference[reference].
Further formating details: see xref:writing-rules-mk[the writing
rules].
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