docs/build.tex

   1 One of the biggest challenges to getting started with embedded devices is that you
   2 cannot just install a copy of Linux and expect to be able to compile a firmware.
   3 Even if you did remember to install a compiler and every development tool offered,
   4 you still would not have the basic set of tools needed to produce a firmware image.
   5 The embedded device represents an entirely new hardware platform, which is
   6 most of the time incompatible with the hardware on your development machine, so in a process called
   7 cross compiling you need to produce a new compiler capable of generating code for
   8 your embedded platform, and then use it to compile a basic Linux distribution to
   9 run on your device.
  10
  11 The process of creating a cross compiler can be tricky, it is not something that is
  12 regularly attempted and so there is a certain amount of mystery and black magic
  13 associated with it. In many cases when you are dealing with embedded devices you will
  14 be provided with a binary copy of a compiler and basic libraries rather than
  15 instructions for creating your own -- it is a time saving step but at the same time
  16 often means you will be using a rather dated set of tools. Likewise, it is also common
  17 to be provided with a patched copy of the Linux kernel from the board or chip vendor,
  18 but this is also dated and it can be difficult to spot exactly what has been
  19 modified to make the kernel run on the embedded platform.
  20
  21 \subsection{Building an image}
  22
  23 OpenWrt takes a different approach to building a firmware; downloading, patching
  24 and compiling everything from scratch, including the cross compiler. To put it
  25 in simpler terms, OpenWrt does not contain any executables or even sources, it is an
  26 automated system for downloading the sources, patching them to work with the given
  27 platform and compiling them correctly for that platform. What this means is that
  28 just by changing the template, you can change any step in the process.
  29
  30 As an example, if a new kernel is released, a simple change to one of the Makefiles
  31 will download the latest kernel, patch it to run on the embedded platform and produce
  32 a new firmware image -- there is no work to be done trying to track down an unmodified
  33 copy of the existing kernel to see what changes had been made, the patches are
  34 already provided and the process ends up almost completely transparent. This does not
  35 just apply to the kernel, but to anything included with OpenWrt -- It is this one
  36 simple understated concept which is what allows OpenWrt to stay on the bleeding edge
  37 with the latest compilers, latest kernels and latest applications.
  38
  39 So let's take a look at OpenWrt and see how this all works.
  40
  41
  42 \subsubsection{Download OpenWrt}
  43
  44 OpenWrt can be downloaded via subversion using the following command:
  45
  46 \begin{Verbatim}
  47 $ svn checkout svn://svn.openwrt.org/openwrt/trunk openwrt-trunk
  48 \end{Verbatim}
  49
  50 Additionally, there is a trac interface on \href{https://dev.openwrt.org/}{https://dev.openwrt.org/}
  51 which can be used to monitor svn commits and browse the source repository.
  52
  53
  54 \subsubsection{The directory structure}
  55
  56 There are four key directories in the base:
  57
  58 \begin{itemize}
  59     \item \texttt{tools}
  60     \item \texttt{toolchain}
  61     \item \texttt{package}
  62     \item \texttt{target}
  63 \end{itemize}
  64
  65 \texttt{tools} and \texttt{toolchain} refer to common tools which will be
  66 used to build the firmware image, the compiler, and the C library.
  67 The result of this is three new directories, \texttt{build\_dir/host}, which is a temporary
  68 directory for building the target independent tools, \texttt{build\_dir/toolchain-\textit{<arch>}*}
  69 which is used for building the toolchain for a specific architecture, and
  70 \texttt{staging\_dir/toolchain-\textit{<arch>}*} where the resulting toolchain is installed.
  71 You will not need to do anything with the toolchain directory unless you intend to
  72 add a new version of one of the components above.
  73
  74 \begin{itemize}
  75     \item \texttt{build\_dir/host}
  76     \item \texttt{build\_dir/toolchain-\textit{<arch>}*}
  77 \end{itemize}
  78
  79 \texttt{package} is for exactly that -- packages. In an OpenWrt firmware, almost everything
  80 is an \texttt{.ipk}, a software package which can be added to the firmware to provide new
  81 features or removed to save space. Note that packages are also maintained outside of the main
  82 trunk and can be obtained from subversion using the package feeds system:
  83
  84 \begin{Verbatim}
  85 $ ./scripts/feeds update
  86 \end{Verbatim}
  87
  88 Those packages can be used to extend the functionality of the build system and need to be
  89 symlinked into the main trunk. Once you do that, the packages will show up in the menu for
  90 configuration. You would do something like this:
  91
  92 \begin{Verbatim}
  93 $ ./scripts/feeds search nmap
  94 Search results in feed 'packages':
  95 nmap       Network exploration and/or security auditing utility
  96
  97 $ ./scripts/feeds install nmap
  98 \end{Verbatim}
  99
 100 To include all packages, issue the following command:
 101
 102 \begin{Verbatim}
 103 $ make package/symlinks
 104 \end{Verbatim}
 105
 106 \texttt{target} refers to the embedded platform, this contains items which are specific to
 107 a specific embedded platform. Of particular interest here is the "\texttt{target/linux}"
 108 directory which is broken down by platform \textit{<arch>} and contains the patches to the
 109 kernel, profile config, for a particular platform. There's also the "\texttt{target/image}" directory
 110 which describes how to package a firmware for a specific platform.
 111
 112 Both the target and package steps will use the directory "\texttt{build\_dir/\textit{<arch>}}"
 113 as a temporary directory for compiling. Additionally, anything downloaded by the toolchain,
 114 target or package steps will be placed in the "\texttt{dl}" directory.
 115
 116 \begin{itemize}
 117     \item \texttt{build\_dir/\textit{<arch>}}
 118     \item \texttt{dl}
 119 \end{itemize}
 120
 121 \subsubsection{Building OpenWrt}
 122
 123 While the OpenWrt build environment was intended mostly for developers, it also has to be
 124 simple enough that an inexperienced end user can easily build his or her own customized firmware.
 125
 126 Running the command "\texttt{make menuconfig}" will bring up OpenWrt's configuration menu
 127 screen, through this menu you can select which platform you're targeting, which versions of
 128 the toolchain you want to use to build and what packages you want to install into the
 129 firmware image. Note that it will also check to make sure you have the basic dependencies for it
 130 to run correctly.  If that fails, you will need to install some more tools in your local environment
 131 before you can begin.
 132
 133 Similar to the linux kernel config, almost every option has three choices,
 134 \texttt{y/m/n} which are represented as follows:
 135
 136 \begin{itemize}
 137     \item{\texttt{<*>} (pressing y)} \\
 138         This will be included in the firmware image
 139     \item{\texttt{<M>} (pressing m)} \\
 140         This will be compiled but not included (for later install)
 141     \item{\texttt{< >} (pressing n)} \\
 142         This will not be compiled
 143 \end{itemize}
 144
 145 After you've finished with the menu configuration, exit and when prompted, save your
 146 configuration changes.
 147
 148 If you want, you can also modify the kernel config for the selected target system.
 149 simply run "\texttt{make kernel\_menuconfig}" and the build system will unpack the kernel sources
 150 (if necessary), run menuconfig inside of the kernel tree, and then copy the kernel config
 151 to \texttt{target/linux/\textit{<platform>}/config} so that it is preserved over
 152 "\texttt{make clean}" calls.
 153
 154 To begin compiling the firmware, type "\texttt{make}". By default
 155 OpenWrt will only display a high level overview of the compile process and not each individual
 156 command.
 157
 158 \subsubsection{Example:}
 159
 160 \begin{Verbatim}
 161 make[2] toolchain/install
 162 make[3] -C toolchain install
 163 make[2] target/compile
 164 make[3] -C target compile
 165 make[4] -C target/utils prepare
 166
 167 [...]
 168 \end{Verbatim}
 169
 170 This makes it easier to monitor which step it's actually compiling and reduces the amount
 171 of noise caused by the compile output. To see the full output, run the command
 172 "\texttt{make V=99}".
 173
 174 During the build process, buildroot will download all sources to the "\texttt{dl}"
 175 directory and will start patching and compiling them in the "\texttt{build\_dir/\textit{<arch>}}"
 176 directory. When finished, the resulting firmware will be in the "\texttt{bin}" directory
 177 and packages will be in the "\texttt{bin/packages}" directory.
 178
 179
 180 \subsection{Creating packages}
 181
 182 One of the things that we've attempted to do with OpenWrt's template system is make it
 183 incredibly easy to port software to OpenWrt. If you look at a typical package directory
 184 in OpenWrt you'll find several things:
 185
 186 \begin{itemize}
 187     \item \texttt{package/\textit{<name>}/Makefile}
 188     \item \texttt{package/\textit{<name>}/patches}
 189     \item \texttt{package/\textit{<name>}/files}
 190 \end{itemize}
 191
 192 The patches directory is optional and typically contains bug fixes or optimizations to
 193 reduce the size of the executable. The package makefile is the important item, provides
 194 the steps actually needed to download and compile the package.
 195
 196 The files directory is also optional and typicall contains package specific startup scripts or default configuration files that can be used out of the box with OpenWrt.
 197
 198 Looking at one of the package makefiles, you'd hardly recognize it as a makefile.
 199 Through what can only be described as blatant disregard and abuse of the traditional
 200 make format, the makefile has been transformed into an object oriented template which
 201 simplifies the entire ordeal.
 202
 203 Here for example, is \texttt{package/bridge/Makefile}:
 204
 205 \begin{Verbatim}[frame=single,numbers=left]
 206
 207 include $(TOPDIR)/rules.mk
 208
 209 PKG_NAME:=bridge
 210 PKG_VERSION:=1.0.6
 211 PKG_RELEASE:=1
 212
 213 PKG_SOURCE:=bridge-utils-$(PKG_VERSION).tar.gz
 214 PKG_SOURCE_URL:=@SF/bridge
 215 PKG_MD5SUM:=9b7dc52656f5cbec846a7ba3299f73bd
 216 PKG_CAT:=zcat
 217
 218 PKG_BUILD_DIR:=$(BUILD_DIR)/bridge-utils-$(PKG_VERSION)
 219
 220 include $(INCLUDE_DIR)/package.mk
 221
 222 define Package/bridge
 223   SECTION:=net
 224   CATEGORY:=Base system
 225   TITLE:=Ethernet bridging configuration utility
 226   URL:=http://bridge.sourceforge.net/
 227 endef
 228
 229 define Package/bridge/description
 230   Manage ethernet bridging:
 231   a way to connect networks together to form a larger network.
 232 endef
 233
 234 define Build/Configure
 235     $(call Build/Configure/Default, \
 236         --with-linux-headers="$(LINUX_DIR)" \
 237     )
 238 endef
 239
 240 define Package/bridge/install
 241     $(INSTALL_DIR) $(1)/usr/sbin
 242     $(INSTALL_BIN) $(PKG_BUILD_DIR)/brctl/brctl $(1)/usr/sbin/
 243 endef
 244
 245 $(eval $(call BuildPackage,bridge))
 246 \end{Verbatim}
 247
 248 As you can see, there's not much work to be done; everything is hidden in other makefiles
 249 and abstracted to the point where you only need to specify a few variables.
 250
 251 \begin{itemize}
 252     \item \texttt{PKG\_NAME} \\
 253         The name of the package, as seen via menuconfig and ipkg
 254     \item \texttt{PKG\_VERSION} \\
 255         The upstream version number that we are downloading
 256     \item \texttt{PKG\_RELEASE} \\
 257         The version of this package Makefile
 258     \item \texttt{PKG\_SOURCE} \\
 259         The filename of the original sources
 260     \item \texttt{PKG\_SOURCE\_URL} \\
 261         Where to download the sources from (no trailing slash), you can add multiple download sources by separating them with a \\ and a carriage return.
 262     \item \texttt{PKG\_MD5SUM} \\
 263         A checksum to validate the download
 264     \item \texttt{PKG\_CAT} \\
 265         How to decompress the sources (zcat, bzcat, unzip)
 266     \item \texttt{PKG\_BUILD\_DIR} \\
 267         Where to compile the package
 268 \end{itemize}
 269
 270 The \texttt{PKG\_*} variables define where to download the package from;
 271 \texttt{@SF} is a special keyword for downloading packages from sourceforge. There is also
 272 another keyword of \texttt{@GNU} for grabbing GNU source releases. If any of the above mentionned download source fails, the OpenWrt mirrors will be used as source.
 273
 274 The md5sum (if present) is used to verify the package was downloaded correctly and
 275 \texttt{PKG\_BUILD\_DIR} defines where to find the package after the sources are
 276 uncompressed into \texttt{\$(BUILD\_DIR)}.
 277
 278 At the bottom of the file is where the real magic happens, "BuildPackage" is a macro
 279 set up by the earlier include statements. BuildPackage only takes one argument directly --
 280 the name of the package to be built, in this case "\texttt{bridge}". All other information
 281 is taken from the define blocks. This is a way of providing a level of verbosity, it's
 282 inherently clear what the contents of the \texttt{description} template in
 283 \texttt{Package/bridge} is, which wouldn't be the case if we passed this information
 284 directly as the Nth argument to \texttt{BuildPackage}.
 285
 286 \texttt{BuildPackage} uses the following defines:
 287
 288 \textbf{\texttt{Package/\textit{<name>}}:} \\
 289     \texttt{\textit{<name>}} matches the argument passed to buildroot, this describes
 290     the package the menuconfig and ipkg entries. Within \texttt{Package/\textit{<name>}}
 291     you can define the following variables:
 292
 293     \begin{itemize}
 294         \item \texttt{SECTION} \\
 295             The section of package (currently unused)
 296         \item \texttt{CATEGORY} \\
 297             Which menu it appears in menuconfig: Network, Sound, Utilities, Multimedia ...
 298         \item \texttt{TITLE} \\
 299             A short description of the package
 300         \item \texttt{URL} \\
 301             Where to find the original software
 302         \item \texttt{MAINTAINER} (optional) \\
 303             Who to contact concerning the package
 304         \item \texttt{DEPENDS} (optional) \\
 305             Which packages must be built/installed before this package. To reference a dependency defined in the
 306                         same Makefile, use \textit{<dependency name>}. If defined as an external package, use
 307                         \textit{+<dependency name>}. For a kernel version dependency use: \textit{@LINUX\_2\_<minor version>}
 308                 \item \texttt{BUILDONLY} (optional) \\
 309                         Set this option to 1 if you do NOT want your package to appear in menuconfig.
 310                         This is useful for packages which are only used as build dependencies.
 311     \end{itemize}
 312
 313 \textbf{\texttt{Package/\textit{<name>}/conffiles} (optional):} \\
 314    A list of config files installed by this package, one file per line.
 315
 316 \textbf{\texttt{Build/Prepare} (optional):} \\
 317    A set of commands to unpack and patch the sources. You may safely leave this
 318    undefined.
 319
 320 \textbf{\texttt{Build/Configure} (optional):} \\
 321    You can leave this undefined if the source doesn't use configure or has a
 322    normal config script, otherwise you can put your own commands here or use
 323    "\texttt{\$(call Build/Configure/Default,\textit{<first list of arguments, second list>})}" as above to
 324    pass in additional arguments for a standard configure script. The first list of arguments will be passed
 325    to the configure script like that: \texttt{--arg 1} \texttt{--arg 2}. The second list contains arguments that should be
 326    defined before running the configure script such as autoconf or compiler specific variables.
 327
 328    To make it easier to modify the configure command line, you can either extend or completely override the following variables:
 329    \begin{itemize}
 330      \item \texttt{CONFIGURE\_ARGS} \\
 331              Contains all command line arguments (format: \texttt{--arg 1} \texttt{--arg 2})
 332      \item \texttt{CONFIGURE\_VARS} \\
 333              Contains all environment variables that are passed to ./configure (format: \texttt{NAME="value"})
 334    \end{itemize}
 335
 336 \textbf{\texttt{Build/Compile} (optional):} \\
 337    How to compile the source; in most cases you should leave this undefined.
 338
 339    As with \texttt{Build/Configure} there are two variables that allow you to override
 340    the make command line environment variables and flags:
 341    \begin{itemize}
 342      \item \texttt{MAKE\_FLAGS} \\
 343            Contains all command line arguments (typically variable overrides like \texttt{NAME="value"}
 344          \item \texttt{MAKE\_VARS} \\
 345            Contains all environment variables that are passed to the make command
 346    \end{itemize}
 347
 348 \textbf{\texttt{Build/InstallDev} (optional):} \\
 349         If your package provides a library that needs to be made available to other packages,
 350         you can use the \texttt{Build/InstallDev} template to copy it into the staging directory
 351         which is used to collect all files that other packages might depend on at build time.
 352         When it is called by the build system, two parameters are passed to it. \texttt{\$(1)} points to
 353         the regular staging dir, typically \texttt{staging\_dir/\textit{ARCH}}, while \texttt{\$(2)} points
 354         to \texttt{staging\_dir/host}. The host staging dir is only used for binaries, which are
 355         to be executed or linked against on the host and its \texttt{bin/} subdirectory is included
 356         in the \texttt{PATH} which is passed down to the build system processes.
 357         Please use \texttt{\$(1)} and \texttt{\$(2)} here instead of the build system variables
 358         \texttt{\$(STAGING\_DIR)} and \texttt{\$(STAGING\_DIR\_HOST)}, because the build system behavior
 359         when staging libraries might change in the future to include automatic uninstallation.
 360
 361 \textbf{\texttt{Package/\textit{<name>}/install}:} \\
 362    A set of commands to copy files out of the compiled source and into the ipkg
 363    which is represented by the \texttt{\$(1)} directory. Note that there are currently
 364    4 defined install macros:
 365    \begin{itemize}
 366        \item \texttt{INSTALL\_DIR} \\
 367            install -d -m0755
 368        \item \texttt{INSTALL\_BIN} \\
 369            install -m0755
 370        \item \texttt{INSTALL\_DATA} \\
 371            install -m0644
 372        \item \texttt{INSTALL\_CONF} \\
 373            install -m0600
 374    \end{itemize}
 375
 376 The reason that some of the defines are prefixed by "\texttt{Package/\textit{<name>}}"
 377 and others are simply "\texttt{Build}" is because of the possibility of generating
 378 multiple packages from a single source. OpenWrt works under the assumption of one
 379 source per package Makefile, but you can split that source into as many packages as
 380 desired. Since you only need to compile the sources once, there's one global set of
 381 "\texttt{Build}" defines, but you can add as many "Package/<name>" defines as you want
 382 by adding extra calls to \texttt{BuildPackage} -- see the dropbear package for an example.
 383
 384 After you have created your \texttt{package/\textit{<name>}/Makefile}, the new package
 385 will automatically show in the menu the next time you run "make menuconfig" and if selected
 386 will be built automatically the next time "\texttt{make}" is run.
 387
 388 \subsection{Creating binary packages}
 389
 390 You might want to create binary packages and include them in the resulting images as packages.
 391 To do so, you can use the following template, which basically sets to nothing the Configure and
 392 Compile templates.
 393
 394 \begin{Verbatim}[frame=single,numbers=left]
 395
 396 include $(TOPDIR)/rules.mk
 397
 398 PKG_NAME:=binpkg
 399 PKG_VERSION:=1.0
 400 PKG_RELEASE:=1
 401
 402 PKG_SOURCE:=binpkg-$(PKG_VERSION).tar.gz
 403 PKG_SOURCE_URL:=http://server
 404 PKG_MD5SUM:=9b7dc52656f5cbec846a7ba3299f73bd
 405 PKG_CAT:=zcat
 406
 407 include $(INCLUDE_DIR)/package.mk
 408
 409 define Package/binpkg
 410   SECTION:=net
 411   CATEGORY:=Network
 412   TITLE:=Binary package
 413 endef
 414
 415 define Package/bridge/description
 416   Binary package
 417 endef
 418
 419 define Build/Configure
 420 endef
 421
 422 define Build/Compile
 423 endef
 424
 425 define Package/bridge/install
 426     $(INSTALL_DIR) $(1)/usr/sbin
 427     $(INSTALL_BIN) $(PKG_BUILD_DIR)/* $(1)/usr/sbin/
 428 endef
 429
 430 $(eval $(call BuildPackage,bridge))
 431 \end{Verbatim}
 432
 433 Provided that the tarball which contains the binaries reflects the final
 434 directory layout (/usr, /lib ...), it becomes very easy to get your package
 435 look like one build from sources.
 436
 437 Note that using the same technique, you can easily create binary pcakages
 438 for your proprietary kernel modules as well.
 439
 440 \subsection{Creating kernel modules packages}
 441
 442 The OpenWrt distribution makes the distinction between two kind of kernel modules, those coming along with the mainline kernel, and the others available as a separate project. We will see later that a common template is used for both of them.
 443
 444 For kernel modules that are part of the mainline kernel source, the makefiles are located in \textit{package/kernel/modules/*.mk} and they appear under the section "Kernel modules"
 445
 446 For external kernel modules, you can add them to the build system just like if they were software packages by defining a KernelPackage section in the package makefile.
 447
 448 Here for instance the Makefile for the I2C subsytem kernel modules :
 449
 450 \begin{Verbatim}[frame=single,numbers=left]
 451
 452 I2CMENU:=I2C Bus
 453
 454 define KernelPackage/i2c-core
 455   TITLE:=I2C support
 456   DESCRIPTION:=Kernel modules for i2c support
 457   SUBMENU:=$(I2CMENU)
 458   KCONFIG:=CONFIG_I2C_CORE CONFIG_I2C_DEV
 459   FILES:=$(MODULES_DIR)/kernel/drivers/i2c/*.$(LINUX_KMOD_SUFFIX)
 460   AUTOLOAD:=$(call AutoLoad,50,i2c-core i2c-dev)
 461 endef
 462 $(eval $(call KernelPackage,i2c-core))
 463 \end{Verbatim}
 464
 465 To group kernel modules under a common description in menuconfig, you might want to define a \textit{<description>MENU} variable on top of the kernel modules makefile.
 466
 467 \begin{itemize}
 468     \item \texttt{TITLE} \\
 469         The name of the module as seen via menuconfig
 470     \item \texttt{DESCRIPTION} \\
 471         The description as seen via help in menuconfig
 472     \item \texttt{SUBMENU} \\
 473         The sub menu under which this package will be seen
 474     \item \texttt{KCONFIG} \\
 475         Kernel configuration option dependency. For external modules, remove it.
 476     \item \texttt{FILES} \\
 477         Files you want to inlude to this kernel module package, separate with spaces.
 478     \item \texttt{AUTOLOAD} \\
 479         Modules that will be loaded automatically on boot, the order you write them is the order they would be loaded.
 480 \end{itemize}
 481
 482 After you have created your \texttt{package/kernel/modules/\textit{<name>}.mk}, the new kernel modules package
 483 will automatically show in the menu under "Kernel modules" next time you run "make menuconfig" and if selected
 484 will be built automatically the next time "\texttt{make}" is run.
 485
 486 \subsection{Conventions}
 487
 488 There are a couple conventions to follow regarding packages:
 489
 490 \begin{itemize}
 491     \item \texttt{files}
 492     \begin{enumerate}
 493         \item configuration files follow the convention \\
 494         \texttt{\textit{<name>}.conf}
 495         \item init files follow the convention \\
 496         \texttt{\textit{<name>}.init}
 497     \end{enumerate}
 498     \item \texttt{patches}
 499     \begin{enumerate}
 500         \item patches are numerically prefixed and named related to what they do
 501     \end{enumerate}
 502 \end{itemize}
 503
 504 \subsection{Troubleshooting}
 505
 506 If you find your package doesn't show up in menuconfig, try the following command to
 507 see if you get the correct description:
 508
 509 \begin{Verbatim}
 510   TOPDIR=$PWD make -C package/<name> DUMP=1 V=99
 511 \end{Verbatim}
 512
 513 If you're just having trouble getting your package to compile, there's a few
 514 shortcuts you can take. Instead of waiting for make to get to your package, you can
 515 run one of the following:
 516
 517 \begin{itemize}
 518     \item \texttt{make package/\textit{<name>}/clean V=99}
 519     \item \texttt{make package/\textit{<name>}/install V=99}
 520 \end{itemize}
 521
 522 Another nice trick is that if the source directory under \texttt{build\_dir/\textit{<arch>}}
 523 is newer than the package directory, it won't clobber it by unpacking the sources again.
 524 If you were working on a patch you could simply edit the sources under the
 525 \texttt{build\_dir/\textit{<arch>}/\textit{<source>}} directory and run the install command above,
 526 when satisfied, copy the patched sources elsewhere and diff them with the unpatched
 527 sources. A warning though - if you go modify anything under \texttt{package/\textit{<name>}}
 528 it will remove the old sources and unpack a fresh copy.
 529
 530 Other useful targets include:
 531
 532 \begin{itemize}
 533     \item \texttt{make package/\textit{<name>}/prepare V=99}
 534     \item \texttt{make package/\textit{<name>}/compile V=99}
 535     \item \texttt{make package/\textit{<name>}/configure V=99}
 536 \end{itemize}
 537
 538
 539 \subsection{Using build environments}
 540 OpenWrt provides a means of building images for multiple configurations
 541 which can use multiple targets in one single checkout. These \emph{environments}
 542 store a copy of the .config file generated by \texttt{make menuconfig} and the contents
 543 of the \texttt{./files} folder.
 544 The script \texttt{./scripts/env} is used to manage these environments, it uses
 545 \texttt{git} (which needs to be installed on your system) as backend for version control.
 546
 547 The command
 548 \begin{Verbatim}
 549   ./scripts/env help
 550 \end{Verbatim}
 551 produces a short help text with a list of commands.
 552
 553 To create a new environment named \texttt{current}, run the following command
 554 \begin{Verbatim}
 555   ./scripts/env new current
 556 \end{Verbatim}
 557 This will move your \texttt{.config} file and \texttt{./files} (if it exists) to
 558 the \texttt{env/} subdirectory and create symlinks in the base folder.
 559
 560 After running make menuconfig or changing things in files/, your current state will
 561 differ from what has been saved before. To show these changes, use:
 562 \begin{Verbatim}
 563   ./scripts/env diff
 564 \end{Verbatim}
 565
 566 If you want to save these changes, run:
 567 \begin{Verbatim}
 568   ./scripts/env save
 569 \end{Verbatim}
 570 If you want to revert your changes to the previously saved copy, run:
 571 \begin{Verbatim}
 572   ./scripts/env revert
 573 \end{Verbatim}
 574
 575 If you want, you can now create a second environment using the \texttt{new} command.
 576 It will ask you whether you want to make it a clone of the current environment (e.g.
 577 for minor changes) or if you want to start with a clean version (e.g. for selecting
 578 a new target).
 579
 580 To switch to a different environment (e.g. \texttt{test1}), use:
 581 \begin{Verbatim}
 582   ./scripts/env switch test1
 583 \end{Verbatim}
 584
 585 To rename the current branch to a new name (e.g. \texttt{test2}), use:
 586 \begin{Verbatim}
 587   ./scripts/env rename test2
 588 \end{Verbatim}
 589
 590 If you want to get rid of environment switching and keep everything in the base directory
 591 again, use:
 592 \begin{Verbatim}
 593   ./scripts/env clear
 594 \end{Verbatim}