--- /dev/null
+.. SPDX-License-Identifier: GPL-2.0
+
+Linux kernel licensing rules
+============================
+
+The Linux Kernel is provided under the terms of the GNU General Public
+License version 2 only (GPL-2.0), as published by the Free Software
+Foundation, and provided in the COPYING file. This documentation file is
+not meant to replace the COPYING file, but provides a description of how
+each source file should be annotated to make the licensing it is governed
+under clear and unambiguous.
+
+The license in the COPYING file applies to the kernel source as a whole,
+though individual source files can have a different license which is
+required to be compatible with the GPL-2.0::
+
+ GPL-1.0+ : GNU General Public License v1.0 or later
+ GPL-2.0+ : GNU General Public License v2.0 or later
+ LGPL-2.0 : GNU Library General Public License v2 only
+ LGPL-2.0+ : GNU Library General Public License v2 or later
+ LGPL-2.1 : GNU Lesser General Public License v2.1 only
+ LGPL-2.1+ : GNU Lesser General Public License v2.1 or later
+
+Aside from that, individual files can be provided under a dual license,
+e.g. one of the compatible GPL variants and alternatively under a
+permissive license like BSD, MIT etc.
+
+The User-space API (UAPI) header files, which describe the interface of
+user-space programs to the kernel are a special case. According to the
+note in the kernel COPYING file, the syscall interface is a clear boundary,
+which does not extend the GPL requirements to any software which uses it to
+communicate with the kernel. Because the UAPI headers must be includable
+into any source files which create an executable running on the Linux
+kernel, the exception must be documented by a special license expression.
+
+The common way of expressing the license of a source file is to add the
+matching boilerplate text into the top comment of the file. Due to
+formatting, typos etc. these "boilerplates" are hard to validate for
+tools which are used in the context of license compliance.
+
+An alternative to boilerplate text is the use of Software Package Data
+Exchange (SPDX) license identifiers in each source file. SPDX license
+identifiers are machine parsable and precise shorthands for the license
+under which the content of the file is contributed. SPDX license
+identifiers are managed by the SPDX Workgroup at the Linux Foundation and
+have been agreed on by partners throughout the industry, tool vendors, and
+legal teams. For further information see https://spdx.org/
+
+The Linux kernel requires the precise SPDX identifier in all source files.
+The valid identifiers used in the kernel are explained in the section
+`License identifiers`_ and have been retrieved from the official SPDX
+license list at https://spdx.org/licenses/ along with the license texts.
+
+License identifier syntax
+-------------------------
+
+1. Placement:
+
+ The SPDX license identifier in kernel files shall be added at the first
+ possible line in a file which can contain a comment. For the majority
+ or files this is the first line, except for scripts which require the
+ '#!PATH_TO_INTERPRETER' in the first line. For those scripts the SPDX
+ identifier goes into the second line.
+
+|
+
+2. Style:
+
+ The SPDX license identifier is added in form of a comment. The comment
+ style depends on the file type::
+
+ C source: // SPDX-License-Identifier: <SPDX License Expression>
+ C header: /* SPDX-License-Identifier: <SPDX License Expression> */
+ ASM: /* SPDX-License-Identifier: <SPDX License Expression> */
+ scripts: # SPDX-License-Identifier: <SPDX License Expression>
+ .rst: .. SPDX-License-Identifier: <SPDX License Expression>
+ .dts{i}: // SPDX-License-Identifier: <SPDX License Expression>
+
+ If a specific tool cannot handle the standard comment style, then the
+ appropriate comment mechanism which the tool accepts shall be used. This
+ is the reason for having the "/\* \*/" style comment in C header
+ files. There was build breakage observed with generated .lds files where
+ 'ld' failed to parse the C++ comment. This has been fixed by now, but
+ there are still older assembler tools which cannot handle C++ style
+ comments.
+
+|
+
+3. Syntax:
+
+ A <SPDX License Expression> is either an SPDX short form license
+ identifier found on the SPDX License List, or the combination of two
+ SPDX short form license identifiers separated by "WITH" when a license
+ exception applies. When multiple licenses apply, an expression consists
+ of keywords "AND", "OR" separating sub-expressions and surrounded by
+ "(", ")" .
+
+ License identifiers for licenses like [L]GPL with the 'or later' option
+ are constructed by using a "+" for indicating the 'or later' option.::
+
+ // SPDX-License-Identifier: GPL-2.0+
+ // SPDX-License-Identifier: LGPL-2.1+
+
+ WITH should be used when there is a modifier to a license needed.
+ For example, the linux kernel UAPI files use the expression::
+
+ // SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note
+ // SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note
+
+ Other examples using WITH exceptions found in the kernel are::
+
+ // SPDX-License-Identifier: GPL-2.0 WITH mif-exception
+ // SPDX-License-Identifier: GPL-2.0+ WITH GCC-exception-2.0
+
+ Exceptions can only be used with particular License identifiers. The
+ valid License identifiers are listed in the tags of the exception text
+ file. For details see the point `Exceptions`_ in the chapter `License
+ identifiers`_.
+
+ OR should be used if the file is dual licensed and only one license is
+ to be selected. For example, some dtsi files are available under dual
+ licenses::
+
+ // SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
+
+ Examples from the kernel for license expressions in dual licensed files::
+
+ // SPDX-License-Identifier: GPL-2.0 OR MIT
+ // SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
+ // SPDX-License-Identifier: GPL-2.0 OR Apache-2.0
+ // SPDX-License-Identifier: GPL-2.0 OR MPL-1.1
+ // SPDX-License-Identifier: (GPL-2.0 WITH Linux-syscall-note) OR MIT
+ // SPDX-License-Identifier: GPL-1.0+ OR BSD-3-Clause OR OpenSSL
+
+ AND should be used if the file has multiple licenses whose terms all
+ apply to use the file. For example, if code is inherited from another
+ project and permission has been given to put it in the kernel, but the
+ original license terms need to remain in effect::
+
+ // SPDX-License-Identifier: (GPL-2.0 WITH Linux-syscall-note) AND MIT
+
+ Another other example where both sets of license terms need to be
+ adhered to is::
+
+ // SPDX-License-Identifier: GPL-1.0+ AND LGPL-2.1+
+
+License identifiers
+-------------------
+
+The licenses currently used, as well as the licenses for code added to the
+kernel, can be broken down into:
+
+1. _`Preferred licenses`:
+
+ Whenever possible these licenses should be used as they are known to be
+ fully compatible and widely used. These licenses are available from the
+ directory::
+
+ LICENSES/preferred/
+
+ in the kernel source tree.
+
+ The files in this directory contain the full license text and
+ `Metatags`_. The file names are identical to the SPDX license
+ identifier which shall be used for the license in source files.
+
+ Examples::
+
+ LICENSES/preferred/GPL-2.0
+
+ Contains the GPL version 2 license text and the required metatags::
+
+ LICENSES/preferred/MIT
+
+ Contains the MIT license text and the required metatags
+
+ _`Metatags`:
+
+ The following meta tags must be available in a license file:
+
+ - Valid-License-Identifier:
+
+ One or more lines which declare which License Identifiers are valid
+ inside the project to reference this particular license text. Usually
+ this is a single valid identifier, but e.g. for licenses with the 'or
+ later' options two identifiers are valid.
+
+ - SPDX-URL:
+
+ The URL of the SPDX page which contains additional information related
+ to the license.
+
+ - Usage-Guidance:
+
+ Freeform text for usage advice. The text must include correct examples
+ for the SPDX license identifiers as they should be put into source
+ files according to the `License identifier syntax`_ guidelines.
+
+ - License-Text:
+
+ All text after this tag is treated as the original license text
+
+ File format examples::
+
+ Valid-License-Identifier: GPL-2.0
+ Valid-License-Identifier: GPL-2.0+
+ SPDX-URL: https://spdx.org/licenses/GPL-2.0.html
+ Usage-Guide:
+ To use this license in source code, put one of the following SPDX
+ tag/value pairs into a comment according to the placement
+ guidelines in the licensing rules documentation.
+ For 'GNU General Public License (GPL) version 2 only' use:
+ SPDX-License-Identifier: GPL-2.0
+ For 'GNU General Public License (GPL) version 2 or any later version' use:
+ SPDX-License-Identifier: GPL-2.0+
+ License-Text:
+ Full license text
+
+ ::
+
+ SPDX-License-Identifier: MIT
+ SPDX-URL: https://spdx.org/licenses/MIT.html
+ Usage-Guide:
+ To use this license in source code, put the following SPDX
+ tag/value pair into a comment according to the placement
+ guidelines in the licensing rules documentation.
+ SPDX-License-Identifier: MIT
+ License-Text:
+ Full license text
+
+|
+
+2. Not recommended licenses:
+
+ These licenses should only be used for existing code or for importing
+ code from a different project. These licenses are available from the
+ directory::
+
+ LICENSES/other/
+
+ in the kernel source tree.
+
+ The files in this directory contain the full license text and
+ `Metatags`_. The file names are identical to the SPDX license
+ identifier which shall be used for the license in source files.
+
+ Examples::
+
+ LICENSES/other/ISC
+
+ Contains the Internet Systems Consortium license text and the required
+ metatags::
+
+ LICENSES/other/ZLib
+
+ Contains the ZLIB license text and the required metatags.
+
+ Metatags:
+
+ The metatag requirements for 'other' licenses are identical to the
+ requirements of the `Preferred licenses`_.
+
+ File format example::
+
+ Valid-License-Identifier: ISC
+ SPDX-URL: https://spdx.org/licenses/ISC.html
+ Usage-Guide:
+ Usage of this license in the kernel for new code is discouraged
+ and it should solely be used for importing code from an already
+ existing project.
+ To use this license in source code, put the following SPDX
+ tag/value pair into a comment according to the placement
+ guidelines in the licensing rules documentation.
+ SPDX-License-Identifier: ISC
+ License-Text:
+ Full license text
+
+|
+
+3. _`Exceptions`:
+
+ Some licenses can be amended with exceptions which grant certain rights
+ which the original license does not. These exceptions are available
+ from the directory::
+
+ LICENSES/exceptions/
+
+ in the kernel source tree. The files in this directory contain the full
+ exception text and the required `Exception Metatags`_.
+
+ Examples::
+
+ LICENSES/exceptions/Linux-syscall-note
+
+ Contains the Linux syscall exception as documented in the COPYING
+ file of the Linux kernel, which is used for UAPI header files.
+ e.g. /\* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note \*/::
+
+ LICENSES/exceptions/GCC-exception-2.0
+
+ Contains the GCC 'linking exception' which allows to link any binary
+ independent of its license against the compiled version of a file marked
+ with this exception. This is required for creating runnable executables
+ from source code which is not compatible with the GPL.
+
+ _`Exception Metatags`:
+
+ The following meta tags must be available in an exception file:
+
+ - SPDX-Exception-Identifier:
+
+ One exception identifier which can be used with SPDX license
+ identifiers.
+
+ - SPDX-URL:
+
+ The URL of the SPDX page which contains additional information related
+ to the exception.
+
+ - SPDX-Licenses:
+
+ A comma separated list of SPDX license identifiers for which the
+ exception can be used.
+
+ - Usage-Guidance:
+
+ Freeform text for usage advice. The text must be followed by correct
+ examples for the SPDX license identifiers as they should be put into
+ source files according to the `License identifier syntax`_ guidelines.
+
+ - Exception-Text:
+
+ All text after this tag is treated as the original exception text
+
+ File format examples::
+
+ SPDX-Exception-Identifier: Linux-syscall-note
+ SPDX-URL: https://spdx.org/licenses/Linux-syscall-note.html
+ SPDX-Licenses: GPL-2.0, GPL-2.0+, GPL-1.0+, LGPL-2.0, LGPL-2.0+, LGPL-2.1, LGPL-2.1+
+ Usage-Guidance:
+ This exception is used together with one of the above SPDX-Licenses
+ to mark user-space API (uapi) header files so they can be included
+ into non GPL compliant user-space application code.
+ To use this exception add it with the keyword WITH to one of the
+ identifiers in the SPDX-Licenses tag:
+ SPDX-License-Identifier: <SPDX-License> WITH Linux-syscall-note
+ Exception-Text:
+ Full exception text
+
+ ::
+
+ SPDX-Exception-Identifier: GCC-exception-2.0
+ SPDX-URL: https://spdx.org/licenses/GCC-exception-2.0.html
+ SPDX-Licenses: GPL-2.0, GPL-2.0+
+ Usage-Guidance:
+ The "GCC Runtime Library exception 2.0" is used together with one
+ of the above SPDX-Licenses for code imported from the GCC runtime
+ library.
+ To use this exception add it with the keyword WITH to one of the
+ identifiers in the SPDX-Licenses tag:
+ SPDX-License-Identifier: <SPDX-License> WITH GCC-exception-2.0
+ Exception-Text:
+ Full exception text
+
+
+All SPDX license identifiers and exceptions must have a corresponding file
+in the LICENSE subdirectories. This is required to allow tool
+verification (e.g. checkpatch.pl) and to have the licenses ready to read
+and extract right from the source, which is recommended by various FOSS
+organizations, e.g. the `FSFE REUSE initiative <https://reuse.software/>`_.
projects / linux-2.6-microblaze.git / blobdiff