docs: kernel_abi.py: add a script to parse ABI documentation

The ABI documentation is special: it is not plain text files,
but, instead, files with an strict format, as specified by
Documentation/ABI/README.

Add a parser for it.
Acked-by: NJonathan Corbet <corbet@lwn.net>
Signed-off-by: NMauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/48abf1a410237e63f85354a8cd7027fdf25657bf.1604042072.git.mchehab+huawei@kernel.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/sphinx/kernel_abi.py

+# -*- coding: utf-8; mode: python -*-
+# SPDX-License-Identifier: GPL-2.0
+u"""
+    kernel-abi
+    ~~~~~~~~~~
+
+    Implementation of the ``kernel-abi`` reST-directive.
+
+    :copyright:  Copyright (C) 2016  Markus Heiser
+    :copyright:  Copyright (C) 2016-2020  Mauro Carvalho Chehab
+    :maintained-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
+    :license:    GPL Version 2, June 1991 see Linux/COPYING for details.
+
+    The ``kernel-abi`` (:py:class:`KernelCmd`) directive calls the
+    scripts/get_abi.pl script to parse the Kernel ABI files.
+
+    Overview of directive's argument and options.
+
+    .. code-block:: rst
+
+        .. kernel-abi:: <ABI directory location>
+            :debug:
+
+    The argument ``<ABI directory location>`` is required. It contains the
+    location of the ABI files to be parsed.
+
+    ``debug``
+      Inserts a code-block with the *raw* reST. Sometimes it is helpful to see
+      what reST is generated.
+
+"""
+
+import sys
+import os
+from os import path
+import subprocess
+
+from sphinx.ext.autodoc import AutodocReporter
+
+from docutils import nodes
+from docutils.parsers.rst import Directive, directives
+from docutils.statemachine import ViewList
+from docutils.utils.error_reporting import ErrorString
+
+
+__version__  = '1.0'
+
+# We can't assume that six is installed
+PY3 = sys.version_info[0] == 3
+PY2 = sys.version_info[0] == 2
+if PY3:
+    # pylint: disable=C0103, W0622
+    unicode     = str
+    basestring  = str
+
+def setup(app):
+
+    app.add_directive("kernel-abi", KernelCmd)
+    return dict(
+        version = __version__
+        , parallel_read_safe = True
+        , parallel_write_safe = True
+    )
+
+class KernelCmd(Directive):
+
+    u"""KernelABI (``kernel-abi``) directive"""
+
+    required_arguments = 1
+    optional_arguments = 0
+    has_content = False
+    final_argument_whitespace = True
+
+    option_spec = {
+        "debug"     : directives.flag
+    }
+
+    def warn(self, message, **replace):
+        replace["fname"]   = self.state.document.current_source
+        replace["line_no"] = replace.get("line_no", self.lineno)
+        message = ("%(fname)s:%(line_no)s: [kernel-abi WARN] : " + message) % replace
+        self.state.document.settings.env.app.warn(message, prefix="")
+
+    def run(self):
+
+        doc = self.state.document
+        if not doc.settings.file_insertion_enabled:
+            raise self.warning("docutils: file insertion disabled")
+
+        env = doc.settings.env
+        cwd = path.dirname(doc.current_source)
+        cmd = "get_abi.pl rest --dir "
+        cmd += self.arguments[0]
+
+        srctree = path.abspath(os.environ["srctree"])
+
+        fname = cmd
+
+        # extend PATH with $(srctree)/scripts
+        path_env = os.pathsep.join([
+            srctree + os.sep + "scripts",
+            os.environ["PATH"]
+        ])
+        shell_env = os.environ.copy()
+        shell_env["PATH"]    = path_env
+        shell_env["srctree"] = srctree
+
+        lines = self.runCmd(cmd, shell=True, cwd=cwd, env=shell_env)
+        nodeList = self.nestedParse(lines, fname)
+        return nodeList
+
+    def runCmd(self, cmd, **kwargs):
+        u"""Run command ``cmd`` and return it's stdout as unicode."""
+
+        try:
+            proc = subprocess.Popen(
+                cmd
+                , stdout = subprocess.PIPE
+                , stderr = subprocess.PIPE
+                , universal_newlines = True
+                , **kwargs
+            )
+            out, err = proc.communicate()
+            if err:
+                self.warn(err)
+            if proc.returncode != 0:
+                raise self.severe(
+                    u"command '%s' failed with return code %d"
+                    % (cmd, proc.returncode)
+                )
+        except OSError as exc:
+            raise self.severe(u"problems with '%s' directive: %s."
+                              % (self.name, ErrorString(exc)))
+        return unicode(out)
+
+    def nestedParse(self, lines, fname):
+        content = ViewList()
+        node    = nodes.section()
+
+        if "debug" in self.options:
+            code_block = "\n\n.. code-block:: rst\n    :linenos:\n"
+            for l in lines.split("\n"):
+                code_block += "\n    " + l
+            lines = code_block + "\n\n"
+
+        for c, l in enumerate(lines.split("\n")):
+            content.append(l, fname, c)
+
+        buf  = self.state.memo.title_styles, self.state.memo.section_level, self.state.memo.reporter
+        self.state.memo.title_styles  = []
+        self.state.memo.section_level = 0
+        self.state.memo.reporter      = AutodocReporter(content, self.state.memo.reporter)
+        try:
+            self.state.nested_parse(content, 0, node, match_titles=1)
+        finally:
+            self.state.memo.title_styles, self.state.memo.section_level, self.state.memo.reporter = buf
+        return node.children