84 lines
3.4 KiB
Plaintext
84 lines
3.4 KiB
Plaintext
// -*- mode:doc; -*-
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// vim: set syntax=asciidoc:
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=== Using Buildroot during development
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The normal operation of Buildroot is to download a tarball, extract
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it, configure, compile and install the software component found inside
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this tarball. The source code is extracted in
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+output/build/<package>-<version>+, which is a temporary directory:
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whenever +make clean+ is used, this directory is entirely removed, and
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re-recreated at the next +make+ invocation. Even when a Git or
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Subversion repository is used as the input for the package source
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code, Buildroot creates a tarball out of it, and then behaves as it
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normally does with tarballs.
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This behavior is well-suited when Buildroot is used mainly as an
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integration tool, to build and integrate all the components of an
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embedded Linux system. However, if one uses Buildroot during the
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development of certain components of the system, this behavior is not
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very convenient: one would instead like to make a small change to the
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source code of one package, and be able to quickly rebuild the system
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with Buildroot.
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Making changes directly in +output/build/<package>-<version>+ is not
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an appropriate solution, because this directory is removed on +make
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clean+.
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Therefore, Buildroot provides a specific mechanism for this use case:
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the +<pkg>_OVERRIDE_SRCDIR+ mechanism. Buildroot reads an _override_
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file, which allows the user to tell Buildroot the location of the
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source for certain packages. By default this _override_ file is named
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+local.mk+ and located in the top directory of the Buildroot source
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tree, but a different location can be specified through the
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+BR2_PACKAGE_OVERRIDE_FILE+ configuration option.
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In this _override_ file, Buildroot expects to find lines of the form:
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------------------
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<pkg1>_OVERRIDE_SRCDIR = /path/to/pkg1/sources
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<pkg2>_OVERRIDE_SRCDIR = /path/to/pkg2/sources
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------------------
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For example:
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------------------
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LINUX_OVERRIDE_SRCDIR = /home/bob/linux/
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BUSYBOX_OVERRIDE_SRCDIR = /home/bob/busybox/
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------------------
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When Buildroot finds that for a given package, an
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+<pkg>_OVERRIDE_SRCDIR+ has been defined, it will no longer attempt to
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download, extract and patch the package. Instead, it will directly use
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the source code available in in the specified directory and +make
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clean+ will not touch this directory. This allows to point Buildroot
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to your own directories, that can be managed by Git, Subversion, or
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any other version control system. To achieve this, Buildroot will use
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_rsync_ to copy the source code of the component from the specified
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+<pkg>_OVERRIDE_SRCDIR+ to +output/build/<package>-custom/+.
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This mechanism is best used in conjunction with the +make
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<pkg>-rebuild+ and +make <pkg>-reconfigure+ targets. A +make
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<pkg>-rebuild all+ sequence will _rsync_ the source code from
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+<pkg>_OVERRIDE_SRCDIR+ to +output/build/<package>-custom+ (thanks to
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_rsync_, only the modified files are copied), and restart the build
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process of just this package.
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In the example of the +linux+ package above, the developer can then
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make a source code change in +/home/bob/linux+ and then run:
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-----------------------
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make linux-rebuild all
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-----------------------
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and in a matter of seconds gets the updated Linux kernel image in
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+output/images+. Similarly, a change can be made to the BusyBox source
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code in +/home/bob/busybox+, and after:
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-----------------------
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make busybox-rebuild all
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-----------------------
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the root filesystem image in +output/images+ contains the updated
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BusyBox.
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