LICENSES: add 'license-rules.txt'

Add a file to the LICENSES directory to describe how file licenses
should be described in all the OpenOCD files, using the SPDX
identifier, as well as where all licenses should be in the source
tree for people to refer to (LICENSES/).

This file is mainly copied from the Linux kernel file in
	Documentation/process/license-rules.rst
originally written by Thomas Gleixner <tglx@linutronix.de>, with
specific adaptations for OpenOCD.

Change-Id: I7a98fc756df90dc86dbc6e0c47c009a610a0318d
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5973
Tested-by: jenkins
Reviewed-by: Tim Newsome <tim@sifive.com>

COPYING

@@ -7,4 +7,10 @@ later, according with:
 
 	LICENSES/preferred/GPL-2.0
 
+In addition, other licenses may also apply. Please see:
+
+	LICENSES/license-rules.txt
+
+for more details.
+
 All contributions to OpenOCD are subject to this COPYING file.

LICENSES/license-rules.txt

@@ -0,0 +1,218 @@
+# SPDX-License-Identifier: GPL-2.0-or-later OR GFDL-1.2-no-invariants-or-later
+
+OpenOCD licensing rules
+=======================
+
+The OpenOCD source code is provided under the terms of the GNU General
+Public License version 2 or later (GPL-2.0-or-later), as provided in
+LICENSES/preferred/GPL-2.0.
+
+The OpenOCD documentation is provided under the terms of the GNU Free
+Documentation License version 1.2 or later without Invariant Sections
+(GFDL-1.2-no-invariants-or-later).
+
+Few stand-alone applications coexist in the same code tree of OpenOCD
+and are provided under the terms of the GNU General Public License
+version 3 (GPL-3.0), as provided in LICENSES/stand-alone/GPL-3.0.
+
+This documentation file provides a description of how each source file
+should be annotated to make its license clear and unambiguous.
+It doesn't replace the OpenOCD's license.
+
+The license described in the COPYING file applies to the OpenOCD 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-or-later  : GNU General Public License v1.0 or later
+    GPL-2.0-or-later  : GNU General Public License v2.0 or later
+    LGPL-2.0          : GNU Library General Public License v2 only
+    LGPL-2.0-or-later : GNU Library General Public License v2 or later
+    LGPL-2.1          : GNU Lesser General Public License v2.1 only
+    LGPL-2.1-or-later : 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 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/
+
+OpenOCD requires the precise SPDX identifier in all source files.
+The valid identifiers used in OpenOCD 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 OpenOCD files shall be added at the
+   first possible line in a file which can contain a comment. For the
+   majority of 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> */
+      makefiles: # SPDX-License-Identifier: <SPDX License Expression>
+      scripts:   # SPDX-License-Identifier: <SPDX License Expression>
+      texinfo:   @c SPDX-License-Identifier: <SPDX License Expression>
+      text:      # 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 "-or-later":
+
+      // SPDX-License-Identifier: GPL-2.0-or-later
+      // SPDX-License-Identifier: LGPL-2.1-or-later
+
+   WITH should be used when there is a modifier to a license needed.
+   Exceptions can only be used with particular License identifiers. The
+   valid License identifiers are listed in the tags of the exception text
+   file.
+
+   OR should be used if the file is dual licensed and only one license is
+   to be selected. For example, some source files are available under dual
+   licenses:
+
+      // SPDX-License-Identifier: GPL-2.0-or-later OR BSD-1-Clause
+      // SPDX-License-Identifier: GPL-2.0-or-later OR BSD-2-Clause
+      // SPDX-License-Identifier: GPL-2.0-or-later OR BSD-3-Clause
+
+   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 OpenOCD, but the
+   original license terms need to remain in effect::
+
+      // SPDX-License-Identifier: GPL-2.0-or-later AND MIT
+
+License identifiers
+-------------------
+
+The licenses currently used, as well as the licenses for code added to
+OpenOCD, 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 OpenOCD 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.
+
+   `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-only
+      Valid-License-Identifier: GPL-2.0-or-later
+      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
+        or
+          SPDX-License-Identifier: GPL-2.0-only
+        For 'GNU General Public License (GPL) version 2 or any later version' use:
+          SPDX-License-Identifier: GPL-2.0-or-later
+      License-Text:
+        Full license text
+
+2. Stand-alone licenses:
+
+   These licenses should only be used for stand-alone applications that are
+   distributed with OpenOCD but are not included in the OpenOCD binary.
+   These licenses are available from the directory:
+
+     LICENSES/stand-alone/
+
+   in the OpenOCD source tree.
+
+   Examples:
+
+     SPDX-License-Identifier: GPL-3.0
+
+The format and requirements of the license files in the other sub-directories
+of directory
+
+   LICENSES
+
+have to follow the same format and requirements of the `Preferred licenses`.
+
+All SPDX license identifiers and exceptions must have a corresponding file
+in the LICENSES 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/>`.

Makefile.am

@@ -50,6 +50,7 @@ EXTRA_DIST += \
 	README.macOS \
 	$(EXTRA_DIST_NEWS) \
 	Doxyfile.in \
+	LICENSES/license-rules.txt \
 	LICENSES/preferred/BSD-1-Clause \
 	LICENSES/preferred/BSD-2-Clause \
 	LICENSES/preferred/BSD-3-Clause \