openwrt/docs/buildroot-documentation.html

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  15       <h1>OpenWrt Buildroot</h1>
  16     </div>
  17
  18     <p>Usage and documentation by Felix Fietkau, based on uClibc Buildroot
  19     documentation by Thomas Petazzoni. Contributions from Karsten Kruse,
  20     Ned Ludd, Martin Herren.</p>
  21
  22     <p><small>Last modification : $Id$</small></p>
  23
  24     <ul>
  25       <li><a href="#about">About OpenWrt Buildroot</a></li>
  26       <li><a href="#download">Obtaining OpenWrt Buildroot</a></li>
  27       <li><a href="#using">Using OpenWrt Buildroot</a></li>
  28       <li><a href="#custom_targetfs">Customizing the target filesystem</a></li>
  29       <li><a href="#custom_busybox">Customizing the Busybox
  30       configuration</a></li>
  31       <li><a href="#custom_uclibc">Customizing the uClibc
  32       configuration</a></li>
  33       <li><a href="#buildroot_innards">How OpenWrt Buildroot works</a></li>
  34       <li><a href="#using_toolchain">Using the uClibc toolchain</a></li>
  35       <li><a href="#toolchain_standalone">Using the uClibc toolchain
  36       outside of Buildroot</a></li>
  37       <li><a href="#downloaded_packages">Location of downloaded packages</a></li>
  38       <li><a href="#add_software">Extending OpenWrt with more Software</a></li>
  39       <li><a href="#links">Ressources</a></li>
  40     </ul>
  41
  42     <h2><a name="about" id="about"></a>About OpenWrt Buildroot</h2>
  43
  44     <p>OpenWrt Buildroot is a set of Makefiles and patches that allows to easily
  45     generate both a cross-compilation toolchain and a root filesystem for your
  46     Wireless Router. The cross-compilation toolchain uses uClibc (<a href=
  47     "http://www.uclibc.org/">http://www.uclibc.org/</a>), a tiny C standard
  48     library.</p>
  49
  50     <p>A compilation toolchain is the set of tools that allows to
  51     compile code for your system. It consists of a compiler (in our
  52     case, <code>gcc</code>), binary utils like assembler and linker
  53     (in our case, <code>binutils</code>) and a C standard library (for
  54     example <a href="http://www.gnu.org/software/libc/libc.html">GNU
  55     Libc</a>, <a href="http://www.uclibc.org">uClibc</a> or <a
  56     href="http://www.fefe.de/dietlibc/">dietlibc</a>). The system
  57     installed on your development station certainly already has a
  58     compilation toolchain that you can use to compile application that
  59     runs on your system. If you're using a PC, your compilation
  60     toolchain runs on an x86 processor and generates code for a x86
  61     processor. Under most Linux systems, the compilation toolchain
  62     uses the GNU libc as C standard library.  This compilation
  63     toolchain is called the "host compilation toolchain", and more
  64     generally, the machine on which it is running, and on which you're
  65     working is called the "host system". The compilation toolchain is
  66     provided by your distribution, and OpenWrt Buildroot has nothing to do
  67     with it.</p>
  68
  69     <p>As said above, the compilation toolchain that comes with your system
  70     runs and generates code for the processor of your host system. As your
  71     embedded system has a different processor, you need a cross-compilation
  72     toolchain: it's a compilation toolchain that runs on your host system but
  73     that generates code for your target system (and target processor). For
  74     example, if your host system uses x86 and your target system uses MIPS, the
  75     regular compilation toolchain of your host runs on x86 and generates code
  76     for x86, while the cross-compilation toolchain runs on x86 and generates
  77     code for MIPS.</p>
  78
  79     <p>You might wonder why such a tool is needed when you can compile
  80     <code>gcc</code>, <code>binutils</code>, uClibc and all the tools by hand.
  81     Of course, doing so is possible. But dealing with all configure options,
  82     with all problems of every <code>gcc</code> or <code>binutils</code>
  83     version is very time-consuming and uninteresting. OpenWrt Buildroot automates this
  84     process through the use of Makefiles, and has a collection of patches for
  85     each <code>gcc</code> and <code>binutils</code> version to make them work
  86     on the MIPS architecture of most Wireless Routers.</p>
  87
  88     <h2><a name="download" id="download"></a>Obtaining OpenWrt Buildroot</h2>
  89
  90     <p>OpenWrt Buildroot is available via CVS - Concurrent Version System.
  91     For any kind of development you should get the latest version from cvs via:</p>
  92 <pre>
  93  $ cvs -d:pserver:anonymous@openwrt.org:/openwrt co openwrt
  94 </pre>
  95
  96     <h2><a name="using" id="using"></a>Using OpenWrt Buildroot</h2>
  97
  98     <p>OpenWrt Buildroot has a nice configuration tool similar to the one you can find
  99     in the Linux Kernel (<a href="http://www.kernel.org/">http://www.kernel.org/</a>)
 100     or in Busybox (<a href="http://www.busybox.org/">http://www.busybox.org/</a>).
 101     Note that you can run everything as a normal user. There is no need to be root to
 102     configure and use the Buildroot. The first step is to run the configuration
 103     assistant:</p>
 104
 105 <pre>
 106  $ make menuconfig
 107 </pre>
 108
 109     <p>For each entry of the configuration tool, you can find associated help
 110     that describes the purpose of the entry.</p>
 111
 112     <p>Once everything is configured, the configuration tool has generated a
 113     <code>.config</code> file that contains the description of your
 114     configuration. It will be used by the Makefiles to do what's needed.</p>
 115
 116     <p>Let's go:</p>
 117
 118 <pre>
 119  $ make
 120 </pre>
 121
 122     <p>This command will download, configure and compile all the selected
 123     tools, and finally generate target firmware images and additional packages
 124     (depending on your selections in <code>make menuconfig</code>.
 125     All the target files can be found in the <code>bin/</code> subdirectory.
 126     You can compile firmware images containing two different filesystem types:
 127     <ul>
 128         <li>jffs2</li>
 129         <li>squashfs</li>
 130     </ul>
 131     <p><code>jffs2</code> contains a writable root filesystem, which will expand to
 132     the size of your flash image. Note that you if you use the generic firmware
 133     Image, you need to pick the right image for your Flash size, because of different
 134     eraseblock sizes.</p>
 135
 136     <p><code>squashfs</code> contains a read-only root filesystem using a modified
 137     <code>squashfs</code> filesystem with LZMA compression. When booting it, you can
 138     create a writable second filesystem, which will contain your modifications to
 139     the root filesystem, including the packages you install.
 140
 141     <h2><a name="custom_targetfs" id="custom_targetfs"></a>Customizing the
 142     target filesystem</h2>
 143
 144     <p>There are two ways to customize the resulting target filesystem:</p>
 145
 146     <ul>
 147       <li>Customize the target filesystem directly, and rebuild the image. The
 148       target filesystem is available under <code>build_ARCH/root/</code> where
 149       <code>ARCH</code> is the chosen target architecture, usually mipsel.
 150       You can simply make your changes here, and run make target_install afterwards,
 151       which will rebuild the target filesystem image. This method allows to do
 152       everything on the target filesystem, but if you decide to rebuild your toolchain,
 153       tools or packages, these changes will be lost.</li>
 154
 155       <li>Customize the target filesystem skeleton, available under
 156       <code>target/default/target_skeleton/</code>. You can customize
 157       configuration files or other stuff here. However, the full file hierarchy
 158       is not yet present, because it's created during the compilation process.
 159       So you can't do everything on this target filesystem skeleton, but
 160       changes to it remains even when you completely rebuild the cross-compilation
 161       toolchain and the tools.<br />
 162     </ul>
 163
 164     <h2><a name="custom_busybox" id="custom_busybox"></a>Customizing the
 165     Busybox configuration</h2>
 166
 167     <p>Busybox is very configurable, and you may want to customize it.
 168     Its configuration is completely integrated into the main menuconfig system.
 169     You can find it under "OpenWrt Package Selection" =&gt; "Busybox Configuration"</p>
 170
 171     <h2><a name="custom_uclibc" id="custom_uclibc"></a>Customizing the uClibc
 172     configuration</h2>
 173
 174     <p>Just like <a href="#custom_busybox">BusyBox</a>, <a
 175     href="http://www.uclibc.org">uClibc</a> offers a lot of
 176     configuration options. They allow to select various
 177     functionalities, depending on your needs and limitations.</p>
 178
 179     <p>The easiest way to modify the configuration of uClibc is to
 180     follow these steps :</p>
 181
 182     <ol>
 183
 184       <li>Make a first compilation of buildroot without trying to
 185       customize uClibc.</li>
 186
 187       <li>Go into the directory
 188       <code>toolchain_build_ARCH/uClibc/</code> and run <code>make
 189       menuconfig</code>. The nice configuration assistant, similar to
 190       the one used in the Linux Kernel appears. Make
 191       your configuration as appropriate.</li>
 192
 193       <li>Copy the <code>.config</code> file to
 194       <code>toolchain/uClibc/uClibc.config</code> or
 195       <code>toolchain/uClibc/uClibc.config-locale</code>. The former
 196       is used if you haven't selected locale support in the Buildroot
 197       configuration, and the latter is used if you have selected
 198       locale support.</li>
 199
 200       <li>Run the compilation again</li>
 201
 202     </ol>
 203
 204     <p>Otherwise, you can simply change
 205     <code>toolchain/uClibc/uClibc.config</code> or
 206     <code>toolchain/uClibc/uClibc.config-locale</code> without running
 207     the configuration assistant.</p>
 208
 209     <h2><a name="buildroot_innards" id="buildroot_innards"></a>How OpenWrt Buildroot
 210     works</h2>
 211
 212     <p>As said above, OpenWrt is basically a set of Makefiles that download,
 213     configure and compiles software with the correct options. It also includes
 214     some patches for various software, mainly the ones involved in the
 215     cross-compilation tool chain (<code>gcc</code>, <code>binutils</code> and
 216     uClibc).</p>
 217
 218     <p>There is basically one Makefile per software, and they are named <code>Makefile</code>.
 219     Makefiles are split into three sections:</p>
 220
 221     <ul>
 222       <li><b>package</b> (in the <code>package/</code> directory) contains the
 223       Makefiles and associated files for all user-space tools that Buildroot
 224       can compile and add to the target root filesystem. There is one
 225       sub-directory per tool.</li>
 226
 227       <li><b>toolchain</b> (in the <code>toolchain/</code> directory) contains
 228       the Makefiles and associated files for all software related to the
 229       cross-compilation toolchain : <code>binutils</code>, <code>ccache</code>,
 230       <code>gcc</code>, <code>gdb</code>, <code>kernel-headers</code> and
 231       <code>uClibc</code>.</li>
 232
 233       <li><b>target</b> (in the <code>target</code> directory) contains the
 234       Makefiles and associated files for software related to the generation of
 235       the target root filesystem image. Two types of filesystems are supported
 236       : jffs2 and squashfs.
 237     </ul>
 238
 239     <p>Each directory contains at least 2 files :</p>
 240
 241     <ul>
 242       <li><code>Makefile</code> is the Makefile that downloads, configures,
 243       compiles and installs the software <code>something</code>.</li>
 244
 245       <li><code>Config.in</code> is a part of the configuration tool
 246       description file. It describes the option related to the current
 247       software.</li>
 248     </ul>
 249
 250     <p>The main Makefile do the job through the following steps (once the
 251     configuration is done):</p>
 252
 253     <ol>
 254       <li>Create the download directory (<code>dl/</code> by default). This is
 255       where the tarballs will be downloaded. It is interesting to know that the
 256       tarballs are in this directory because it may be useful to save them
 257       somewhere to avoid further downloads.</li>
 258
 259       <li>Create the build directory (<code>build_ARCH/</code> by default,
 260       where <code>ARCH</code> is your architecture). This is where all
 261       user-space tools while be compiled.</li>
 262
 263       <li>Create the toolchain build directory
 264       (<code>toolchain_build_ARCH/</code> by default, where <code>ARCH</code>
 265       is your architecture). This is where the cross compilation toolchain will
 266       be compiled.</li>
 267
 268       <li>Setup the staging directory (<code>staging_dir_ARCH/</code> by
 269       default). This is where the cross-compilation toolchain will be
 270       installed. If you want to use the same cross-compilation toolchain for
 271       other purposes, such as compiling third-party applications, you can add
 272       <code>staging_dir_ARCH/bin</code> to your PATH, and then use
 273       <code>arch-linux-gcc</code> to compile your application. In order to
 274       setup this staging directory, it first removes it, and then it creates
 275       various subdirectories and symlinks inside it.</li>
 276
 277       <li>Create the target directory (<code>build_ARCH/root/</code> by
 278       default) and the target filesystem skeleton. This directory will contain
 279       the final root filesystem. To setup it up, it first deletes it, then it
 280       copies the skeleton available in  <code>target/default/target_skeleton</code>
 281       and then removes useless <code>CVS/</code> directories.</li>
 282
 283       <li>Call the <code>prepare</code>, <code>compile</code> and <code>install</code>
 284       targets for the subdirectories <code>toolchain</code>, <code>package</code>
 285       and <code>target</code></li>
 286     </ol>
 287
 288     <h2><a name="using_toolchain" id="using_toolchain"></a>Using the
 289     uClibc toolchain</h2>
 290
 291     <p>You may want to compile your own programs or other software
 292     that are not packaged in OpenWrt. In order to do this, you can
 293     use the toolchain that was generated by the Buildroot.</p>
 294
 295     <p>The toolchain generated by the Buildroot by default is located in
 296     <code>staging_dir_ARCH</code>. The simplest way to use it
 297     is to add <code>staging_dir_ARCH/bin/</code> to your PATH
 298     environment variable, and then to use
 299     <code>arch-linux-gcc</code>, <code>arch-linux-objdump</code>,
 300     <code>arch-linux-ld</code>, etc.</p>
 301
 302     <p>For example, you may add the following to your
 303     <code>.bashrc</code> (considering you're building for the MIPS
 304     architecture and that Buildroot is located in
 305     <code>~/buildroot/</code>) :</p>
 306
 307 <pre>
 308 export PATH=$PATH:~/buildroot/staging_dir_mipsel/bin/
 309 </pre>
 310
 311     <p>Then you can simply do :</p>
 312
 313 <pre>
 314 mipsel-linux-uclibc-gcc -o foo foo.c
 315 </pre>
 316
 317     <p><b>Important</b> : do not try to move the toolchain to an other
 318     directory, it won't work. There are some hard-coded paths in the
 319     <i>gcc</i> configuration. If the default toolchain directory
 320     doesn't suit your needs, please refer to the <a
 321     href="#toolchain_standalone">Using the uClibc toolchain outside of
 322     buildroot</a> section.</p>
 323
 324     <h2><a name="toolchain_standalone" id="toolchain_standalone"></a>Using the
 325     uClibc toolchain outside of buildroot</h2>
 326
 327     <p>By default, the cross-compilation toolchain is generated inside
 328     <code>staging_dir_ARCH/</code>. But sometimes, it may be useful to
 329     install it somewhere else, so that it can be used to compile other programs
 330     or by other users. Moving the <code>staging_dir_ARCH/</code>
 331     directory elsewhere is <b>not possible</b>, because they are some hardcoded
 332     paths in the toolchain configuration.</p>
 333
 334     <p>If you want to use the generated toolchain for other purposes,
 335     you can configure Buildroot to generate it elsewhere using the
 336     option of the configuration tool : <code>Build options -&gt;
 337     Toolchain and header file location</code>, which defaults to
 338     <code>staging_dir_ARCH/</code>.</p>
 339
 340     <h2><a name="downloaded_packages"
 341     id="downloaded_packages"></a>Location of downloaded packages</h2>
 342
 343     <p>It might be useful to know that the various tarballs that are
 344     downloaded by the <i>Makefiles</i> are all stored in the
 345     <code>DL_DIR</code> which by default is the <code>dl</code>
 346     directory. It's useful for example if you want to keep a complete
 347     version of Buildroot which is know to be working with the
 348     associated tarballs. This will allow you to regenerate the
 349     toolchain and the target filesystem with exactly the same
 350     versions.</p>
 351
 352     <h2><a name="add_software" id="add_software"></a>Extending OpenWrt with
 353     more software</h2>
 354
 355     <p>This section will only consider the case in which you want to
 356     add user-space software.</p>
 357
 358     <h3>Package directory</h3>
 359
 360     <p>First of all, create a directory under the <code>package</code>
 361     directory for your software, for example <code>foo</code>.</p>
 362
 363     <h3><code>Config.in</code> file</h3>
 364
 365     <p>Then, create a file named <code>Config.in</code>. This file
 366     will contain the portion of options description related to our
 367     <code>foo</code> software that will be used and displayed in the
 368     configuration tool. It should basically contain :</p>
 369
 370 <pre>
 371 config BR2_PACKAGE_FOO
 372         tristate "foo"
 373         default n
 374         help
 375              This is a comment that explains what foo is.
 376 </pre>
 377
 378     <p>Of course, you can add other options to configure particular
 379     things in your software.</p>
 380
 381     <h3><code>Makefile</code> in the package directory</h3>
 382
 383     <p>To add your package to the build process, you need to edit
 384     the Makefile in the <code>package/</code> directory. Locate the
 385     lines that look like the following:</p>
 386
 387 <pre>
 388 package-$(BR2_PACKAGE_FOO) += foo
 389 </pre>
 390
 391    <p>As you can see, this short line simply adds the target
 392    <code>foo</code> to the list of targets handled by OpenWrt Buildroot.</p>
 393
 394
 395     <p>In addition to the default dependencies, you make your package
 396     depend on another package (e.g. a library) by adding a line:
 397
 398 <pre>
 399 foo-compile: bar-compile
 400 </pre>
 401
 402    <h3>The <i>.control</i> file</h3>
 403    <p>Additionally, you need to create a control file which contains
 404    information about your package, readable by the <i>ipkg</i> package
 405    utility.</p>
 406
 407    <p>The file looks like this</p>
 408
 409 <pre>
 410      1  Package: foo
 411      2  Priority: optional
 412      3  Section: net
 413      4  Maintainer: Foo Software &lt;foo@foosoftware.com&gt;
 414      5  Source: http://foosoftware.com
 415      6  Description: Your Package Description
 416 </pre>
 417
 418    <p>You can skip the usual <code>Version:</code> and <code>Architecture</code>
 419    fields, as they will be generated by the <code>make-ipkg-dir.sh</code> script
 420    called from your Makefile</p>
 421
 422    <h3>The real <i>Makefile</i></h3>
 423
 424    <p>Finally, here's the hardest part. Create a file named
 425    <code>Makefile</code>. It will contain the <i>Makefile</i> rules that
 426    are in charge of downloading, configuring, compiling and installing
 427    the software. Below is an example that we will comment
 428    afterwards.</p>
 429
 430 <pre>
 431      1  # $Id$
 432      2  include $(TOPDIR)/rules.mk
 433      3  PKG_NAME:=foo
 434      4  PKG_VERSION:=1.0
 435      5  PKG_RELEASE:=1
 436      6  PKG_MD5SUM:=4584f226523776a3cdd2fb6f8212ba8d
 437      7
 438      8  PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 439      9  PKG_SOURCE_URL:=http://www.foosoftware.org/downloads
 440     10  PKG_DIR:=$(BUILD_DIR)/$(PKG_NAME)-$(PKG_VERSION)
 441     11  PKG_IPK:=$(PACKAGE_DIR)/$(PKG_NAME)_$(PKG_VERSION)-$(PKG_RELEASE)_$(ARCH).ipk
 442     12  PKG_IPK_DIR:=$(PKG_DIR)/ipkg
 443     13
 444     14  $(DL_DIR)/$(PKG_SOURCE):
 445     15          $(SCRIPT_DIR)/download.pl $(DL_DIR) $(PKG_SOURCE) $(PKG_MD5SUM) $(PKG_SOURCE_URL)
 446     16
 447     17  $(PKG_DIR)/.source: $(DL_DIR)/$(PKG_SOURCE)
 448     18          zcat $(DL_DIR)/$(PKG_SOURCE) | tar -C $(BUILD_DIR) $(TAR_OPTIONS) -
 449     19          touch $(PKG_DIR)/.source
 450     20
 451     21  $(PKG_DIR)/.configured: $(PKG_DIR)/.source
 452     22          (cd $(PKG_DIR); \
 453     23                  $(TARGET_CONFIGURE_OPTS) \
 454     24                  CFLAGS="$(TARGET_CFLAGS)" \
 455     25                  ./configure \
 456     26                  --target=$(GNU_TARGET_NAME) \
 457     27                  --host=$(GNU_TARGET_NAME) \
 458     28                  --build=$(GNU_HOST_NAME) \
 459     29                  --prefix=/usr \
 460     30                  --sysconfdir=/etc \
 461     31          );
 462     32          touch $(PKG_DIR)/.configured;
 463     33
 464     34  $(PKG_DIR)/$(PKG_NAME): $(PKG_DIR)/.configured
 465     35          $(MAKE) CC=$(TARGET_CC) -C $(PKG_DIR)
 466     36
 467     37  $(PKG_IPK): $(PKG_DIR)/$(PKG_NAME)
 468     38          $(SCRIPT_DIR)/make-ipkg-dir.sh $(PKG_IPK_DIR) $(PKG_NAME).control $(PKG_VERSION)-$(PKG_RELEASE) $(ARCH)
 469     39          $(MAKE) prefix=$(PKG_IPK_DIR)/usr -C $(PKG_DIR) install
 470     40          rm -Rf $(PKG_IPK_DIR)/usr/man
 471     41          $(IPKG_BUILD) $(PKG_IPK_DIR) $(PACKAGE_DIR)
 472     42
 473     43  $(IPKG_STATE_DIR)/info/$(PKG_NAME).list: $(PKG_IPK)
 474     44          $(IPKG) install $(PKG_IPK)
 475     45
 476     46  prepare: $(PKG_DIR)/.source
 477     47  compile: $(PKG_IPK)
 478     48  install: $(IPKG_STATE_DIR)/info/$(PKG_NAME).list
 479     49  clean:
 480     50          rm -rf $(PKG_DIR)
 481     51          rm -f $(PKG_IPK)
 482 </pre>
 483
 484     <p>First of all, this <i>Makefile</i> example works for a single
 485     binary software. For other software such as libraries or more
 486     complex stuff with multiple binaries, it should be adapted. Look at
 487     the other <code>Makefile</code> files in the <code>package</code>
 488     directory.</p>
 489
 490     <p>At lines 3-12, a couple of useful variables are defined :</p>
 491
 492     <ul>
 493      <li><code>PKG_NAME</code> : The package name, e.g. <i>foo</i>.</li>
 494
 495      <li><code>PKG_VERSION</code> : The version of the package that
 496      should be downloaded.</li>
 497
 498      <li><code>PKG_RELEASE</code> : The release number that will be
 499      appended to the version number of your <i>ipkg</i> package.
 500
 501      <li><code>PKG_MD5SUM</code> : The md5sum of the software archive.
 502
 503      <li><code>PKG_SOURCE</code> : The name of the tarball of
 504      your package on the download website of FTP site. As you can see
 505      <code>PKG_NAME</code> and <code>PKG_VERSION</code> are used.</li>
 506
 507      <li><code>PKG_SOURCE_URL</code> : Space separated list of the HTTP
 508      or FTP sites from which the archive is downloaded. It must include the complete
 509      path to the directory where <code>FOO_SOURCE</code> can be
 510      found.</li>
 511
 512      <li><code>PKG_DIR</code> : The directory into which the software
 513      will be configured and compiled. Basically, it's a subdirectory
 514      of <code>BUILD_DIR</code> which is created upon decompression of
 515      the tarball.</li>
 516
 517      <li><code>PKG_IPK</code> : The resulting <i>ipkg</i> package
 518
 519     </ul>
 520
 521     <p>Lines 14-15 defines a target that downloads the tarball from
 522     the remote site to the download directory
 523     (<code>DL_DIR</code>).</p>
 524
 525     <p>Lines 17-19 defines a target and associated rules that
 526     uncompress the downloaded tarball. As you can see, this target
 527     depends on the tarball file, so that the previous target (line
 528     14-15) is called before executing the rules of the current
 529     target. Uncompressing is followed by <i>touching</i> a hidden file
 530     to mark the software has having been uncompressed. This trick is
 531     used everywhere in Buildroot <i>Makefile</i> to split steps
 532     (download, uncompress, configure, compile, install) while still
 533     having correct dependencies.</p>
 534
 535     <p>Lines 21-32 defines a target and associated rules that
 536     configures the software. It depends on the previous target (the
 537     hidden <code>.source</code> file) so that we are sure the software has
 538     been uncompressed. In order to configure it, it basically runs the
 539     well-known <code>./configure</code>script. As we may be doing
 540     cross-compilation, <code>target</code>, <code>host</code> and
 541     <code>build</code> arguments are given. The prefix is also set to
 542     <code>/usr</code>, not because the software will be installed in
 543     <code>/usr</code> on your host system, but in the target
 544     filesystem. Finally it creates a <code>.configured</code> file to
 545     mark the software as configured.</p>
 546
 547     <p>Lines 34-35 defines a target and a rule that compiles the
 548     software. This target will create the binary file in the
 549     compilation directory, and depends on the software being already
 550     configured (hence the reference to the <code>.configured</code>
 551     file). It basically runs <code>make</code> inside the source
 552     directory.</p>
 553
 554     <p>Lines 37-41 defines a target and associated rules that create
 555     the <i>ipkg</i> package which can optionally be embedded into
 556     the resulting firmware image. It depends on the binary file in
 557     the source directory, to make sure the software has been compiled.
 558     It uses the make-ipkg-dir.sh script, which will create the ipkg
 559     build directory for your package, copy your control file into
 560     that directory and add version and architecture information.
 561     Then it calls the <code>install</code> target of the
 562     software <code>Makefile</code> by passing a <code>prefix</code>
 563     argument, so that the <code>Makefile</code> doesn't try to install
 564     the software inside host <code>/usr</code> but inside target
 565     <code>/usr</code>. After the installation, the
 566     <code>/usr/man</code> directory inside the target filesystem is
 567     removed to save space.
 568     Finally <code>IPKG_BUILD</code> is called to create the package.</p>
 569
 570     <p>Line 43 and 44 define the installation target of your package,
 571     which will embed the software into the target filesystem.</p>
 572
 573     <p>Lines 46-51 define the main targets that the Makefile in the
 574     <code>package</code> dir calls.
 575     <ul>
 576       <li><code>prepare</code> : Download and unpack the source</li>
 577       <li><code>compile</code> : Compile the source and create the package</li>
 578       <li><code>install</code> : Embed the package into the target filesystem</li>
 579       <li><code>clean</code> : Remove all the files created by the build process</li>
 580     </ul></p>
 581
 582     <h3>Conclusion</h3>
 583
 584     <p>As you can see, adding a software to buildroot is simply a
 585     matter of writing a <i>Makefile</i> using an already existing
 586     example and to modify it according to the compilation process of
 587     the software.</p>
 588
 589     <p>If you package software that might be useful for other persons,
 590     don't forget to send a patch to OpenWrt developers !</p>
 591
 592      <h2><a name="links" id="links"></a>Resources</h2>
 593
 594     <p>To learn more about OpenWrt Buildroot you can visit this
 595     website: <a href="http://openwrt.org/">http://openwrt.org/</a></p>
 596
 597   </div>
 598 </body>
 599 </html>