// -*- mode:doc; -*-
  // vim: set syntax=asciidoc:
  
  == General Buildroot usage
  
  include::make-tips.txt[]
  
  include::rebuilding-packages.txt[]
  
  === Offline builds
  
  If you intend to do an offline build and just want to download
  all sources that you previously selected in the configurator
  ('menuconfig', 'nconfig', 'xconfig' or 'gconfig'), then issue:
  
  --------------------
   $ make source
  --------------------
  
  You can now disconnect or copy the content of your +dl+
  directory to the build-host.
  
  === Building out-of-tree
  
  As default, everything built by Buildroot is stored in the directory
  +output+ in the Buildroot tree.
  
  Buildroot also supports building out of tree with a syntax similar to
  the Linux kernel. To use it, add +O=<directory>+ to the make command
  line:
  
  --------------------
   $ make O=/tmp/build
  --------------------
  
  Or:
  
  --------------------
   $ cd /tmp/build; make O=$PWD -C path/to/buildroot
  --------------------
  
  All the output files will be located under +/tmp/build+. If the +O+
  path does not exist, Buildroot will create it.
  
  *Note:* the +O+ path can be either an absolute or a relative path, but if it's
  passed as a relative path, it is important to note that it is interpreted
  relative to the main Buildroot source directory, *not* the current working
  directory.
  
  When using out-of-tree builds, the Buildroot +.config+ and temporary
  files are also stored in the output directory. This means that you can
  safely run multiple builds in parallel using the same source tree as
  long as they use unique output directories.
  
  For ease of use, Buildroot generates a Makefile wrapper in the output
  directory - so after the first run, you no longer need to pass +O=<...>+
  and +-C <...>+, simply run (in the output directory):
  
  --------------------
   $ make <target>
  --------------------
  
  [[env-vars]]
  
  === Environment variables
  
  Buildroot also honors some environment variables, when they are passed
  to +make+ or set in the environment:
  
  * +HOSTCXX+, the host C++ compiler to use
  * +HOSTCC+, the host C compiler to use
  * +UCLIBC_CONFIG_FILE=<path/to/.config>+, path to
    the uClibc configuration file, used to compile uClibc, if an
    internal toolchain is being built.
    +
    Note that the uClibc configuration file can also be set from the
    configuration interface, so through the Buildroot +.config+ file; this
    is the recommended way of setting it.
    +
  * +BUSYBOX_CONFIG_FILE=<path/to/.config>+, path to
    the BusyBox configuration file.
    +
    Note that the BusyBox configuration file can also be set from the
    configuration interface, so through the Buildroot +.config+ file; this
    is the recommended way of setting it.
    +
  * +BR2_CCACHE_DIR+ to override the directory where
    Buildroot stores the cached files when using ccache.
    +
  * +BR2_DL_DIR+ to override the directory in which
    Buildroot stores/retrieves downloaded files
    +
    Note that the Buildroot download directory can also be set from the
    configuration interface, so through the Buildroot +.config+ file; this
    is the recommended way of setting it.
  * +BR2_GRAPH_ALT+, if set and non-empty, to use an alternate color-scheme in
    build-time graphs
  * +BR2_GRAPH_OUT+ to set the filetype of generated graphs, either +pdf+ (the
    default), or +png+.
  * +BR2_GRAPH_DEPS_OPTS+ to pass extra options to the dependency graph; see
    xref:graph-depends[] for the accepted options
  * +BR2_GRAPH_DOT_OPTS+ is passed verbatim as options to the +dot+ utility to
    draw the dependency graph.
  
  An example that uses config files located in the toplevel directory and
  in your $HOME:
  
  --------------------
   $ make UCLIBC_CONFIG_FILE=uClibc.config BUSYBOX_CONFIG_FILE=$HOME/bb.config
  --------------------
  
  If you want to use a compiler other than the default +gcc+
  or +g+++ for building helper-binaries on your host, then do
  
  --------------------
   $ make HOSTCXX=g++-4.3-HEAD HOSTCC=gcc-4.3-HEAD
  --------------------
  
  === Dealing efficiently with filesystem images
  
  Filesystem images can get pretty big, depending on the filesystem you choose,
  the number of packages, whether you provisioned free space... Yet, some
  locations in the filesystems images may just be _empty_ (e.g. a long run of
  'zeroes'); such a file is called a _sparse_ file.
  
  Most tools can handle sparse files efficiently, and will only store or write
  those parts of a sparse file that are not empty.
  
  For example:
  
  * +tar+ accepts the +-S+ option to tell it to only store non-zero blocks
    of sparse files:
  ** +tar cf archive.tar -S [files...]+ will efficiently store sparse files
     in a tarball
  ** +tar xf archive.tar -S+ will efficiently store sparse files extracted
     from a tarball
  
  * +cp+ accepts the +--sparse=WHEN+ option (+WHEN+ is one of +auto+,
    +never+ or +always+):
  ** +cp --sparse=always source.file dest.file+ will make +dest.file+ a
     sparse file if +source.file+ has long runs of zeroes
  
  Other tools may have similar options. Please consult their respective man
  pages.
  
  You can use sparse files if you need to store the filesystem images (e.g.
  to transfer from one machine to another), or if you need to send them (e.g.
  to the Q&A team).
  
  Note however that flashing a filesystem image to a device while using the
  sparse mode of +dd+ may result in a broken filesystem (e.g. the block bitmap
  of an ext2 filesystem may be corrupted; or, if you have sparse files in
  your filesystem, those parts may not be all-zeroes when read back). You
  should only use sparse files when handling files on the build machine, not
  when transferring them to an actual device that will be used on the target.
  
  === Graphing the dependencies between packages
  
  [[graph-depends]]
  
  One of Buildroot's jobs is to know the dependencies between packages,
  and make sure they are built in the right order. These dependencies
  can sometimes be quite complicated, and for a given system, it is
  often not easy to understand why such or such package was brought into
  the build by Buildroot.
  
  In order to help understanding the dependencies, and therefore better
  understand what is the role of the different components in your
  embedded Linux system, Buildroot is capable of generating dependency
  graphs.
  
  To generate a dependency graph of the full system you have compiled,
  simply run:
  
  ------------------------
  make graph-depends
  ------------------------
  
  You will find the generated graph in
  +output/graphs/graph-depends.pdf+.
  
  If your system is quite large, the dependency graph may be too complex
  and difficult to read. It is therefore possible to generate the
  dependency graph just for a given package:
  
  ------------------------
  make <pkg>-graph-depends
  ------------------------
  
  You will find the generated graph in
  +output/graph/<pkg>-graph-depends.pdf+.
  
  Note that the dependency graphs are generated using the +dot+ tool
  from the _Graphviz_ project, which you must have installed on your
  system to use this feature. In most distributions, it is available as
  the +graphviz+ package.
  
  By default, the dependency graphs are generated in the PDF
  format. However, by passing the +BR2_GRAPH_OUT+ environment variable, you
  can switch to other output formats, such as PNG, PostScript or
  SVG. All formats supported by the +-T+ option of the +dot+ tool are
  supported.
  
  --------------------------------
  BR2_GRAPH_OUT=svg make graph-depends
  --------------------------------
  
  The +graph-depends+ behaviour can be controlled by setting options in the
  +BR2_GRAPH_DEPS_OPTS+ environment variable. The accepted options are:
  
  * +--depth N+, +-d N+, to limit the dependency depth to +N+ levels. The
    default, +0+, means no limit.
  
  * +--stop-on PKG+, +-s PKG+, to stop the graph on the package +PKG+.
    +PKG+ can be an actual package name, a glob, the keyword 'virtual'
    (to stop on virtual packages), or the keyword 'host' (to stop on
    host packages). The package is still present on the graph, but its
    dependencies are not.
  
  * +--exclude PKG+, +-x PKG+, like +--stop-on+, but also omits +PKG+ from
    the graph.
  
  * +--transitive+, +--no-transitive+, to draw (or not) the transitive
    dependencies. The default is to not draw transitive dependencies.
  
  * +--colours R,T,H+, the comma-separated list of colours to draw the
    root package (+R+), the target packages (+T+) and the host packages
    (+H+). Defaults to: +lightblue,grey,gainsboro+
  
  --------------------------------
  BR2_GRAPH_DEPS_OPTS='-d 3 --no-transitive --colours=red,green,blue' make graph-depends
  --------------------------------
  
  === Graphing the build duration
  
  [[graph-duration]]
  
  When the build of a system takes a long time, it is sometimes useful
  to be able to understand which packages are the longest to build, to
  see if anything can be done to speed up the build. In order to help
  such build time analysis, Buildroot collects the build time of each
  step of each package, and allows to generate graphs from this data.
  
  To generate the build time graph after a build, run:
  
  ----------------
  make graph-build
  ----------------
  
  This will generate a set of files in +output/graphs+ :
  
  * +build.hist-build.pdf+, a histogram of the build time for each
    package, ordered in the build order.
  
  * +build.hist-duration.pdf+, a histogram of the build time for each
    package, ordered by duration (longest first)
  
  * +build.hist-name.pdf+, a histogram of the build time for each
    package, order by package name.
  
  * +build.pie-packages.pdf+, a pie chart of the build time per package
  
  * +build.pie-steps.pdf+, a pie chart of the global time spent in each
    step of the packages build process.
  
  This +graph-build+ target requires the Python Matplotlib and Numpy
  libraries to be installed (+python-matplotlib+ and +python-numpy+ on
  most distributions), and also the +argparse+ module if you're using a
  Python version older than 2.7 (+python-argparse+ on most
  distributions).
  
  By default, the output format for the graph is PDF, but a different
  format can be selected using the +BR2_GRAPH_OUT+ environment variable. The
  only other format supported is PNG:
  
  ----------------
  BR2_GRAPH_OUT=png make graph-build
  ----------------
  
  === Graphing the filesystem size contribution of packages
  
  When your target system grows, it is sometimes useful to understand
  how much each Buildroot package is contributing to the overall root
  filesystem size. To help with such an analysis, Buildroot collects
  data about files installed by each package and using this data,
  generates a graph and CSV files detailing the size contribution of
  the different packages.
  
  To generate these data after a build, run:
  
  ----------------
  make graph-size
  ----------------
  
  This will generate:
  
  * +output/graphs/graph-size.pdf+, a pie chart of the contribution of
    each package to the overall root filesystem size
  
  * +output/graphs/package-size-stats.csv+, a CSV file giving the size
    contribution of each package to the overall root filesystem size
  
  * +output/graphs/file-size-stats.csv+, a CSV file giving the size
    contribution of each installed file to the package it belongs, and
    to the overall filesystem size.
  
  This +graph-size+ target requires the Python Matplotlib library to be
  installed (+python-matplotlib+ on most distributions), and also the
  +argparse+ module if you're using a Python version older than 2.7
  (+python-argparse+ on most distributions).
  
  Just like for the duration graph, a +BR2_GRAPH_OUT+ environment is
  supported to adjust the output file format. See xref:graph-depends[]
  for details about this environment variable.
  
  .Note
  The collected filesystem size data is only meaningful after a complete
  clean rebuild. Be sure to run +make clean all+ before using +make
  graph-size+.
  
  To compare the root filesystem size of two different Buildroot compilations,
  for example after adjusting the configuration or when switching to another
  Buildroot release, use the +size-stats-compare+ script. It takes two
  +file-size-stats.csv+ files (produced by +make graph-size+) as input.
  Refer to the help text of this script for more details:
  
  ----------------
  support/scripts/size-stats-compare -h
  ----------------
  
  include::eclipse-integration.txt[]
  
  include::advanced.txt[]