manual: document usage of the legal-info feature

  You can find some documentation for this syntax in the xref:makedev-syntax[].

  This variable is optional.

* +LIBFOO_LICENSE+ defines the license (or licenses) under which the package

  is released.

  This name will appear in the manifest file produced by +make legal-info+.

  If the license is one of those listed in xref:legal-info[],

  use the same string to make the manifest file uniform.

  Otherwise, describe the license in a precise and concise way, avoiding

  ambiguous names such as +BSD+ which actually name a family of licenses.

  If the root filesystem you generate contains non-opensource packages, you

  can define their license as +PROPRIETARY+: Buildroot will not save any

  licensing info or source code for this package.

  This variable is optional. If it is not defined, +unknown+ will appear in

  the +license+ field of the manifest file for this package.

* +LIBFOO_LICENSE_FILES+ is a space-separated list of files in the package

  tarball that contain the license(s) under which the package is released.

  +make legal-info+ copies all of these files in the +legal-info+ directory.

  See xref:legal-info[] for more information.

  This variable is optional. If it is not defined, a warning will be produced

  to let you know, and +not saved+ will appear in the +license files+ field

  of the manifest file for this package.

The recommended way to define these variables is to use the following

syntax:

--------------------

 $ make HOSTCXX=g++-4.3-HEAD HOSTCC=gcc-4.3-HEAD

--------------------

Complying with opensource licenses

----------------------------------

[[legal-info]]

All of the end products of Buildroot (toolchain, root filesystem, kernel,

bootloaders) contain opensource software, released under various licenses.

Using opensource software gives you the freedom to build rich embedded

systems choosing from a wide range of packages, but also gives some

obligations that you must know and honour.

Some licenses require you to publish the license text in the documentation of

your product. Other require you to redistribute the source code of the

software to those that receive your product.

The exact requirements of each license is documented in each package, and it is

your (or your legal office's) responsibility to comply with these requirements.

To make this easier for you, Buildroot can collect for you some material you

will probably need. To produce this material, after you configured Buildroot

with +make menuconfig+, +make xconfig+ or +make gconfig+, run:

--------------------

make legal-info

--------------------

Buildroot will collect legally-relevant material in your output directory,

under the +legal-info/+ subdirectory.

There you will find:

* A +README+ file, that summarizes the produced material and contains warnings

  about material that Buildroot could not produce.

* +buildroot.config+: this is the Buildroot configuration file that is usually

  produced with +make menuconfig+, and which is necessary to reproduce the

  build.

* The source code for all packages; this is saved in the +sources/+

  subdirectory (except for proprietary packages, whose source code is not

  saved);

  patches applied to some packages by Buildroot are distributed with the

  Buildroot sources and are not duplicated in the +sources/+ subdirectory.

* A manifest file listing the configured packages, their version, license and

  related information.

  Some of these information might be not defined in Buildroot; in this case

  they are clearly marked as "unknown" or similar.

* A +licenses/+ subdirectory, which contains the license text of packages.

  If the license file(s) are not defined in Buildroot, the file is not produced

  and a warning in the +README+ indicates this.

Please note that the aim of the +legal-info+ feature of Buildroot is to

produce all the material that is somehow relevant for legal compliance with the

package licenses. Buildroot does not try to produce the exact material that

you must somehow make public. It does surely produce some more material than is

needed for a strict legal compliance. For example, it produces the source code

for packages released under BSD-like licenses, that you might not want to

redistribute in source form.

Moreover, due to technical limitations, Buildroot does not produce some

material that you will or may need, such as the toolchain source code and the

Buildroot source code itself.

When you run +make legal-info+, Buildroot produces warnings in the +README+

file to inform you of relevant material that could not be saved.

Here is a list of the licenses that are most widely used by packages in

Buildroot, with the name used in the manifest file:

* +GPLv2+:

  http://www.gnu.org/licenses/old-licenses/gpl-2.0.html[

  GNU General Public License, version 2];

* +GPLv2++:

  http://www.gnu.org/licenses/old-licenses/gpl-2.0.html[

  GNU General Public License, version 2]

  or (at your option) any later version;

* +GPLv3+:

  http://www.gnu.org/licenses/gpl.html[

  GNU General Public License, version 3];

* +GPLv3++:

  http://www.gnu.org/licenses/gpl.html[

  GNU General Public License, version 3]

  or (at your option) any later version;

* +GPL+:

  http://www.gnu.org/licenses/gpl.html[

  GNU General Public License] (any version);

* +LGPLv2.1+:

  http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html[

  GNU Lesser General Public License, version 2.1];

* +LGPLv2.1++:

  http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html[

  GNU Lesser General Public License, version 2.1]

  or (at your option) any later version;

* +LGPLv3+:

  http://www.gnu.org/licenses/lgpl.html[

  GNU Lesser General Public License, version 3];

* +LGPLv3++:

  http://www.gnu.org/licenses/lgpl.html[

  GNU Lesser General Public License, version 3]

  or (at your option) any later version;

* +LGPL+:

  http://www.gnu.org/licenses/lgpl.html[

  GNU Lesser General Public License] (any version);

* +BSD-4c+: Original BSD 4-clause license;

* +BSD-3c+: BSD 3-clause license;

* +BSD-2c+: BSD 2-clause license;

* +PROPRIETARY+: marks a non-opensource package;

  Buildroot does not save any licensing info or source code for these packages.