Merge branch 'build-script' into docs-mw

Quoth Mauro:

This series should probably be called:

    "Move the trick-or-treat build hacks accumulated over time
     into a single place and document them."

as this reflects its main goal. As such:

- it places the jobserver logic on a library;
- it removes sphinx/parallel-wrapper.sh;
- the code now properly implements a jobserver-aware logic
  to do the parallelism when called via GNU make, failing back to
  "-j" when there's  no jobserver;
- converts check-variable-fonts.sh to Python and uses it via
  function call;
- drops an extra script to generate man pages, adding a makefile
  target for it;
- ensures that return code is 0 when PDF successfully builds;
- about half of the script is comments and documentation.

I tried to do my best to document all tricks that are inside the
script. This way, the docs build steps is now documented.

It should be noticed that it is out of the scope of this series
to change the implementation. Surely the process can be improved,
but first let's consolidate and document everything on a single
place.

Such script was written in a way that it can be called either
directly or via a Makefile. Running outside Makefile is
interesting specially when debug is needed. The command line
interface replaces the need of having lots of env vars before
calling sphinx-build:

    $ ./tools/docs/sphinx-build-wrapper --help
    usage: sphinx-build-wrapper [-h]
	   [--sphinxdirs SPHINXDIRS [SPHINXDIRS ...]] [--conf CONF]
	   [--builddir BUILDDIR] [--theme THEME] [--css CSS] [--paper {,a4,letter}] [-v]
	   [-j JOBS] [-i] [-V [VENV]]
	   {cleandocs,linkcheckdocs,htmldocs,epubdocs,texinfodocs,infodocs,mandocs,latexdocs,pdfdocs,xmldocs}

    Kernel documentation builder

    positional arguments:
      {cleandocs,linkcheckdocs,htmldocs,epubdocs,texinfodocs,infodocs,mandocs,latexdocs,pdfdocs,xmldocs}
			    Documentation target to build

    options:
      -h, --help            show this help message and exit
      --sphinxdirs SPHINXDIRS [SPHINXDIRS ...]
			    Specific directories to build
      --conf CONF           Sphinx configuration file
      --builddir BUILDDIR   Sphinx configuration file
      --theme THEME         Sphinx theme to use
      --css CSS             Custom CSS file for HTML/EPUB
      --paper {,a4,letter}  Paper size for LaTeX/PDF output
      -v, --verbose         place build in verbose mode
      -j, --jobs JOBS       Sets number of jobs to use with sphinx-build
      -i, --interactive     Change latex default to run in interactive mode
      -V, --venv [VENV]     If used, run Sphinx from a venv dir (default dir: sphinx_latest)

the only mandatory argument is the target, which is identical with
"make" targets.

The call inside Makefile doesn't use the last four arguments. They're
there to help identifying problems at the build:

    -v makes the output verbose;
    -j helps to test parallelism;
    -i runs latexmk in interactive mode, allowing to debug PDF
       build issues;
    -V is useful when testing it with different venvs.

When used with GNU make (or some other make which implements jobserver),
a call like:

    make -j <targets> htmldocs

will make the wrapper to automatically use POSIX jobserver to claim
the number of available job slots, calling sphinx-build with a
"-j" parameter reflecting it. ON such case, the default can be
overriden via SPHINXDIRS argument.

Visiable changes when compared with the old behavior:

When V=0, the only visible difference is that:
- pdfdocs target now returns 0 on success, 1 on failures.
  This addresses an issue over the current process where we
  it always return success even on failures;
- it will now print the name of PDF files that failed to build,
  if any.

In verbose mode, sphinx-build-wrapper and sphinx-build command lines
are now displayed.

1 files changed, 841 insertions, 0 deletions

diff --git a/tools/docs/sphinx-build-wrapper b/tools/docs/sphinx-build-wrapper
new file mode 100755
index 000000000000..3e6d166d4102
--- /dev/null
+++ b/tools/docs/sphinx-build-wrapper
@@ -0,0 +1,841 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2025 Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
+#
+# pylint: disable=R0902, R0912, R0913, R0914, R0915, R0917, C0103
+#
+# Converted from docs Makefile and parallel-wrapper.sh, both under
+# GPLv2, copyrighted since 2008 by the following authors:
+#
+#    Akira Yokosawa <akiyks@gmail.com>
+#    Arnd Bergmann <arnd@arndb.de>
+#    Breno Leitao <leitao@debian.org>
+#    Carlos Bilbao <carlos.bilbao@amd.com>
+#    Dave Young <dyoung@redhat.com>
+#    Donald Hunter <donald.hunter@gmail.com>
+#    Geert Uytterhoeven <geert+renesas@glider.be>
+#    Jani Nikula <jani.nikula@intel.com>
+#    Jan Stancek <jstancek@redhat.com>
+#    Jonathan Corbet <corbet@lwn.net>
+#    Joshua Clayton <stillcompiling@gmail.com>
+#    Kees Cook <keescook@chromium.org>
+#    Linus Torvalds <torvalds@linux-foundation.org>
+#    Magnus Damm <damm+renesas@opensource.se>
+#    Masahiro Yamada <masahiroy@kernel.org>
+#    Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
+#    Maxim Cournoyer <maxim.cournoyer@gmail.com>
+#    Peter Foley <pefoley2@pefoley.com>
+#    Randy Dunlap <rdunlap@infradead.org>
+#    Rob Herring <robh@kernel.org>
+#    Shuah Khan <shuahkh@osg.samsung.com>
+#    Thorsten Blum <thorsten.blum@toblux.com>
+#    Tomas Winkler <tomas.winkler@intel.com>
+
+
+"""
+Sphinx build wrapper that handles Kernel-specific business rules:
+
+- it gets the Kernel build environment vars;
+- it determines what's the best parallelism;
+- it handles SPHINXDIRS
+
+This tool ensures that MIN_PYTHON_VERSION is satisfied. If version is
+below that, it seeks for a new Python version. If found, it re-runs using
+the newer version.
+"""
+
+import argparse
+import locale
+import os
+import re
+import shlex
+import shutil
+import subprocess
+import sys
+
+from concurrent import futures
+from glob import glob
+
+from lib.python_version import PythonVersion
+from lib.latex_fonts import LatexFontChecker
+
+LIB_DIR = "../../scripts/lib"
+SRC_DIR = os.path.dirname(os.path.realpath(__file__))
+
+sys.path.insert(0, os.path.join(SRC_DIR, LIB_DIR))
+
+from jobserver import JobserverExec         # pylint: disable=C0413,C0411,E0401
+
+#
+#  Some constants
+#
+VENV_DEFAULT = "sphinx_latest"
+MIN_PYTHON_VERSION = PythonVersion("3.7").version
+PAPER = ["", "a4", "letter"]
+
+TARGETS = {
+    "cleandocs":     { "builder": "clean" },
+    "linkcheckdocs": { "builder": "linkcheck" },
+    "htmldocs":      { "builder": "html" },
+    "epubdocs":      { "builder": "epub",    "out_dir": "epub" },
+    "texinfodocs":   { "builder": "texinfo", "out_dir": "texinfo" },
+    "infodocs":      { "builder": "texinfo", "out_dir": "texinfo" },
+    "mandocs":       { "builder": "man",     "out_dir": "man" },
+    "latexdocs":     { "builder": "latex",   "out_dir": "latex" },
+    "pdfdocs":       { "builder": "latex",   "out_dir": "latex" },
+    "xmldocs":       { "builder": "xml",     "out_dir": "xml" },
+}
+
+
+#
+# SphinxBuilder class
+#
+
+class SphinxBuilder:
+    """
+    Handles a sphinx-build target, adding needed arguments to build
+    with the Kernel.
+    """
+
+    def get_path(self, path, use_cwd=False, abs_path=False):
+        """
+        Ancillary routine to handle patches the right way, as shell does.
+
+        It first expands "~" and "~user". Then, if patch is not absolute,
+        join self.srctree. Finally, if requested, convert to abspath.
+        """
+
+        path = os.path.expanduser(path)
+        if not path.startswith("/"):
+            if use_cwd:
+                base = os.getcwd()
+            else:
+                base = self.srctree
+
+            path = os.path.join(base, path)
+
+        if abs_path:
+            return os.path.abspath(path)
+
+        return path
+
+    def get_sphinx_extra_opts(self, n_jobs):
+        """
+        Get the number of jobs to be used for docs build passed via command
+        line and desired sphinx verbosity.
+
+        The number of jobs can be on different places:
+
+        1) It can be passed via "-j" argument;
+        2) The SPHINXOPTS="-j8" env var may have "-j";
+        3) if called via GNU make, -j specifies the desired number of jobs.
+           with GNU makefile, this number is available via POSIX jobserver;
+        4) if none of the above is available, it should default to "-jauto",
+           and let sphinx decide the best value.
+        """
+
+        #
+        # SPHINXOPTS env var, if used, contains extra arguments to be used
+        # by sphinx-build time. Among them, it may contain sphinx verbosity
+        # and desired number of parallel jobs.
+        #
+        parser = argparse.ArgumentParser()
+        parser.add_argument('-j', '--jobs', type=int)
+        parser.add_argument('-q', '--quiet', action='store_true')
+
+        #
+        # Other sphinx-build arguments go as-is, so place them
+        # at self.sphinxopts, using shell parser
+        #
+        sphinxopts = shlex.split(os.environ.get("SPHINXOPTS", ""))
+
+        #
+        # Build a list of sphinx args, honoring verbosity here if specified
+        #
+
+        verbose = self.verbose
+        sphinx_args, self.sphinxopts = parser.parse_known_args(sphinxopts)
+        if sphinx_args.quiet is True:
+            verbose = False
+
+        #
+        # If the user explicitly sets "-j" at command line, use it.
+        # Otherwise, pick it from SPHINXOPTS args
+        #
+        if n_jobs:
+            self.n_jobs = n_jobs
+        elif sphinx_args.jobs:
+            self.n_jobs = sphinx_args.jobs
+        else:
+            self.n_jobs = None
+
+        if not verbose:
+            self.sphinxopts += ["-q"]
+
+    def __init__(self, builddir, venv=None, verbose=False, n_jobs=None,
+                 interactive=None):
+        """Initialize internal variables"""
+        self.venv = venv
+        self.verbose = None
+
+        #
+        # Normal variables passed from Kernel's makefile
+        #
+        self.kernelversion = os.environ.get("KERNELVERSION", "unknown")
+        self.kernelrelease = os.environ.get("KERNELRELEASE", "unknown")
+        self.pdflatex = os.environ.get("PDFLATEX", "xelatex")
+
+        #
+        # Kernel main Makefile defines a PYTHON3 variable whose default is
+        # "python3". When set to a different value, it allows running a
+        # diferent version than the default official python3 package.
+        # Several distros package python3xx-sphinx packages with newer
+        # versions of Python and sphinx-build.
+        #
+        # Honor such variable different than default
+        #
+        self.python = os.environ.get("PYTHON3")
+        if self.python == "python3":
+            self.python = None
+
+        if not interactive:
+            self.latexopts = os.environ.get("LATEXOPTS", "-interaction=batchmode -no-shell-escape")
+        else:
+            self.latexopts = os.environ.get("LATEXOPTS", "")
+
+        if not verbose:
+            verbose = bool(os.environ.get("KBUILD_VERBOSE", "") != "")
+
+        if verbose is not None:
+            self.verbose = verbose
+
+        #
+        # Source tree directory. This needs to be at os.environ, as
+        # Sphinx extensions use it
+        #
+        self.srctree = os.environ.get("srctree")
+        if not self.srctree:
+            self.srctree = "."
+            os.environ["srctree"] = self.srctree
+
+        #
+        # Now that we can expand srctree, get other directories as well
+        #
+        self.sphinxbuild = os.environ.get("SPHINXBUILD", "sphinx-build")
+        self.kerneldoc = self.get_path(os.environ.get("KERNELDOC",
+                                                      "scripts/kernel-doc.py"))
+        self.builddir = self.get_path(builddir, use_cwd=True, abs_path=True)
+
+        #
+        # Get directory locations for LaTeX build toolchain
+        #
+        self.pdflatex_cmd = shutil.which(self.pdflatex)
+        self.latexmk_cmd = shutil.which("latexmk")
+
+        self.env = os.environ.copy()
+
+        self.get_sphinx_extra_opts(n_jobs)
+
+        #
+        # If venv command line argument is specified, run Sphinx from venv
+        #
+        if venv:
+            bin_dir = os.path.join(venv, "bin")
+            if not os.path.isfile(os.path.join(bin_dir, "activate")):
+                sys.exit(f"Venv {venv} not found.")
+
+            # "activate" virtual env
+            self.env["PATH"] = bin_dir + ":" + self.env["PATH"]
+            self.env["VIRTUAL_ENV"] = venv
+            if "PYTHONHOME" in self.env:
+                del self.env["PYTHONHOME"]
+            print(f"Setting venv to {venv}")
+
+    def run_sphinx(self, sphinx_build, build_args, *args, **pwargs):
+        """
+        Executes sphinx-build using current python3 command.
+
+        When calling via GNU make, POSIX jobserver is used to tell how
+        many jobs are still available from a job pool. claim all remaining
+        jobs, as we don't want sphinx-build to run in parallel with other
+        jobs.
+
+        Despite that, the user may actually force a different value than
+        the number of available jobs via command line.
+
+        The "with" logic here is used to ensure that the claimed jobs will
+        be freed once subprocess finishes
+        """
+
+        with JobserverExec() as jobserver:
+            if jobserver.claim:
+                #
+                # when GNU make is used, claim available jobs from jobserver
+                #
+                n_jobs = str(jobserver.claim)
+            else:
+                #
+                # Otherwise, let sphinx decide by default
+                #
+                n_jobs = "auto"
+
+            #
+            # If explicitly requested via command line, override default
+            #
+            if self.n_jobs:
+                n_jobs = str(self.n_jobs)
+
+            #
+            # We can't simply call python3 sphinx-build, as OpenSUSE
+            # Tumbleweed uses an ELF binary file (/usr/bin/alts) to switch
+            # between different versions of sphinx-build. So, only call it
+            # prepending "python3.xx" when PYTHON3 variable is not default.
+            #
+            if self.python:
+                cmd = [self.python]
+            else:
+                cmd = []
+
+            cmd += [sphinx_build]
+            cmd += [f"-j{n_jobs}"]
+            cmd += self.sphinxopts
+            cmd += build_args
+
+            if self.verbose:
+                print(" ".join(cmd))
+
+            return subprocess.call(cmd, *args, **pwargs)
+
+    def handle_html(self, css, output_dir, rustdoc):
+        """
+        Extra steps for HTML and epub output.
+
+        For such targets, we need to ensure that CSS will be properly
+        copied to the output _static directory
+        """
+
+        if css:
+            css = os.path.expanduser(css)
+            if not css.startswith("/"):
+                css = os.path.join(self.srctree, css)
+
+            static_dir = os.path.join(output_dir, "_static")
+            os.makedirs(static_dir, exist_ok=True)
+
+            try:
+                shutil.copy2(css, static_dir)
+            except (OSError, IOError) as e:
+                print(f"Warning: Failed to copy CSS: {e}", file=sys.stderr)
+
+        if rustdoc:
+            if "MAKE" in self.env:
+                cmd = [self.env["MAKE"]]
+            else:
+                cmd = ["make", "LLVM=1"]
+
+            cmd += [ "rustdoc"]
+            if self.verbose:
+                print(" ".join(cmd))
+
+            try:
+                subprocess.run(cmd, check=True)
+            except subprocess.CalledProcessError as e:
+                print(f"Ignored errors when building rustdoc: {e}. Is RUST enabled?",
+                      file=sys.stderr)
+
+    def build_pdf_file(self, latex_cmd, from_dir, path):
+        """Builds a single pdf file using latex_cmd"""
+        try:
+            subprocess.run(latex_cmd + [path],
+                            cwd=from_dir, check=True, env=self.env)
+
+            return True
+        except subprocess.CalledProcessError:
+            return False
+
+    def pdf_parallel_build(self, tex_suffix, latex_cmd, tex_files, n_jobs):
+        """Build PDF files in parallel if possible"""
+        builds = {}
+        build_failed = False
+        max_len = 0
+        has_tex = False
+
+        #
+        # LaTeX PDF error code is almost useless for us:
+        # any warning makes it non-zero. For kernel doc builds it always return
+        # non-zero even when build succeeds. So, let's do the best next thing:
+        # Ignore build errors. At the end, check if all PDF files were built,
+        # printing a summary with the built ones and returning 0 if all of
+        # them were actually built.
+        #
+        with futures.ThreadPoolExecutor(max_workers=n_jobs) as executor:
+            jobs = {}
+
+            for from_dir, pdf_dir, entry in tex_files:
+                name = entry.name
+
+                if not name.endswith(tex_suffix):
+                    continue
+
+                name = name[:-len(tex_suffix)]
+                has_tex = True
+
+                future = executor.submit(self.build_pdf_file, latex_cmd,
+                                         from_dir, entry.path)
+                jobs[future] = (from_dir, pdf_dir, name)
+
+            for future in futures.as_completed(jobs):
+                from_dir, pdf_dir, name = jobs[future]
+
+                pdf_name = name + ".pdf"
+                pdf_from = os.path.join(from_dir, pdf_name)
+                pdf_to = os.path.join(pdf_dir, pdf_name)
+                out_name = os.path.relpath(pdf_to, self.builddir)
+                max_len = max(max_len, len(out_name))
+
+                try:
+                    success = future.result()
+
+                    if success and os.path.exists(pdf_from):
+                        os.rename(pdf_from, pdf_to)
+
+                        #
+                        # if verbose, get the name of built PDF file
+                        #
+                        if self.verbose:
+                           builds[out_name] = "SUCCESS"
+                    else:
+                        builds[out_name] = "FAILED"
+                        build_failed = True
+                except futures.Error as e:
+                    builds[out_name] = f"FAILED ({repr(e)})"
+                    build_failed = True
+
+        #
+        # Handle case where no .tex files were found
+        #
+        if not has_tex:
+            out_name = "LaTeX files"
+            max_len = max(max_len, len(out_name))
+            builds[out_name] = "FAILED: no .tex files were generated"
+            build_failed = True
+
+        return builds, build_failed, max_len
+
+    def handle_pdf(self, output_dirs, deny_vf):
+        """
+        Extra steps for PDF output.
+
+        As PDF is handled via a LaTeX output, after building the .tex file,
+        a new build is needed to create the PDF output from the latex
+        directory.
+        """
+        builds = {}
+        max_len = 0
+        tex_suffix = ".tex"
+        tex_files = []
+
+        #
+        # Since early 2024, Fedora and openSUSE tumbleweed have started
+        # deploying variable-font format of "Noto CJK", causing LaTeX
+        # to break with CJK. Work around it, by denying the variable font
+        # usage during xelatex build by passing the location of a config
+        # file with a deny list.
+        #
+        # See tools/docs/lib/latex_fonts.py for more details.
+        #
+        if deny_vf:
+            deny_vf = os.path.expanduser(deny_vf)
+            if os.path.isdir(deny_vf):
+                self.env["XDG_CONFIG_HOME"] = deny_vf
+
+        for from_dir in output_dirs:
+            pdf_dir = os.path.join(from_dir, "../pdf")
+            os.makedirs(pdf_dir, exist_ok=True)
+
+            if self.latexmk_cmd:
+                latex_cmd = [self.latexmk_cmd, f"-{self.pdflatex}"]
+            else:
+                latex_cmd = [self.pdflatex]
+
+            latex_cmd.extend(shlex.split(self.latexopts))
+
+            # Get a list of tex files to process
+            with os.scandir(from_dir) as it:
+                for entry in it:
+                    if entry.name.endswith(tex_suffix):
+                        tex_files.append((from_dir, pdf_dir, entry))
+
+        #
+        # When using make, this won't be used, as the number of jobs comes
+        # from POSIX jobserver. So, this covers the case where build comes
+        # from command line. On such case, serialize by default, except if
+        # the user explicitly sets the number of jobs.
+        #
+        n_jobs = 1
+
+        # n_jobs is either an integer or "auto". Only use it if it is a number
+        if self.n_jobs:
+            try:
+                n_jobs = int(self.n_jobs)
+            except ValueError:
+                pass
+
+        #
+        # When using make, jobserver.claim is the number of jobs that were
+        # used with "-j" and that aren't used by other make targets
+        #
+        with JobserverExec() as jobserver:
+            n_jobs = 1
+
+            #
+            # Handle the case when a parameter is passed via command line,
+            # using it as default, if jobserver doesn't claim anything
+            #
+            if self.n_jobs:
+                try:
+                    n_jobs = int(self.n_jobs)
+                except ValueError:
+                    pass
+
+            if jobserver.claim:
+                n_jobs = jobserver.claim
+
+            builds, build_failed, max_len = self.pdf_parallel_build(tex_suffix,
+                                                                    latex_cmd,
+                                                                    tex_files,
+                                                                    n_jobs)
+
+        #
+        # In verbose mode, print a summary with the build results per file.
+        # Otherwise, print a single line with all failures, if any.
+        # On both cases, return code 1 indicates build failures,
+        #
+        if self.verbose:
+            msg = "Summary"
+            msg += "\n" + "=" * len(msg)
+            print()
+            print(msg)
+
+            for pdf_name, pdf_file in builds.items():
+                print(f"{pdf_name:<{max_len}}: {pdf_file}")
+
+            print()
+            if build_failed:
+                msg = LatexFontChecker().check()
+                if msg:
+                    print(msg)
+
+                sys.exit("Error: not all PDF files were created.")
+
+        elif build_failed:
+            n_failures = len(builds)
+            failures = ", ".join(builds.keys())
+
+            msg = LatexFontChecker().check()
+            if msg:
+                print(msg)
+
+            sys.exit(f"Error: Can't build {n_failures} PDF file(s): {failures}")
+
+    def handle_info(self, output_dirs):
+        """
+        Extra steps for Info output.
+
+        For texinfo generation, an additional make is needed from the
+        texinfo directory.
+        """
+
+        for output_dir in output_dirs:
+            try:
+                subprocess.run(["make", "info"], cwd=output_dir, check=True)
+            except subprocess.CalledProcessError as e:
+                sys.exit(f"Error generating info docs: {e}")
+
+    def handle_man(self, kerneldoc, docs_dir, src_dir, output_dir):
+        """
+        Create man pages from kernel-doc output
+        """
+
+        re_kernel_doc = re.compile(r"^\.\.\s+kernel-doc::\s*(\S+)")
+        re_man = re.compile(r'^\.TH "[^"]*" (\d+) "([^"]*)"')
+
+        if docs_dir == src_dir:
+            #
+            # Pick the entire set of kernel-doc markups from the entire tree
+            #
+            kdoc_files = set([self.srctree])
+        else:
+            kdoc_files = set()
+
+            for fname in glob(os.path.join(src_dir, "**"), recursive=True):
+                if os.path.isfile(fname) and fname.endswith(".rst"):
+                    with open(fname, "r", encoding="utf-8") as in_fp:
+                        data = in_fp.read()
+
+                    for line in data.split("\n"):
+                        match = re_kernel_doc.match(line)
+                        if match:
+                            if os.path.isfile(match.group(1)):
+                                kdoc_files.add(match.group(1))
+
+        if not kdoc_files:
+                sys.exit(f"Directory {src_dir} doesn't contain kernel-doc tags")
+
+        cmd = [ kerneldoc, "-m" ] + sorted(kdoc_files)
+        try:
+            if self.verbose:
+                print(" ".join(cmd))
+
+            result = subprocess.run(cmd, stdout=subprocess.PIPE, text= True)
+
+            if result.returncode:
+                print(f"Warning: kernel-doc returned {result.returncode} warnings")
+
+        except (OSError, ValueError, subprocess.SubprocessError) as e:
+            sys.exit(f"Failed to create man pages for {src_dir}: {repr(e)}")
+
+        fp = None
+        try:
+            for line in result.stdout.split("\n"):
+                match = re_man.match(line)
+                if not match:
+                    if fp:
+                        fp.write(line + '\n')
+                    continue
+
+                if fp:
+                    fp.close()
+
+                fname = f"{output_dir}/{match.group(2)}.{match.group(1)}"
+
+                if self.verbose:
+                    print(f"Creating {fname}")
+                fp = open(fname, "w", encoding="utf-8")
+                fp.write(line + '\n')
+        finally:
+            if fp:
+                fp.close()
+
+    def cleandocs(self, builder):           # pylint: disable=W0613
+        """Remove documentation output directory"""
+        shutil.rmtree(self.builddir, ignore_errors=True)
+
+    def build(self, target, sphinxdirs=None,
+              theme=None, css=None, paper=None, deny_vf=None, rustdoc=False,
+              skip_sphinx=False):
+        """
+        Build documentation using Sphinx. This is the core function of this
+        module. It prepares all arguments required by sphinx-build.
+        """
+
+        builder = TARGETS[target]["builder"]
+        out_dir = TARGETS[target].get("out_dir", "")
+
+        #
+        # Cleandocs doesn't require sphinx-build
+        #
+        if target == "cleandocs":
+            self.cleandocs(builder)
+            return
+
+        if theme:
+            os.environ["DOCS_THEME"] = theme
+
+        #
+        # Other targets require sphinx-build, so check if it exists
+        #
+        if not skip_sphinx:
+            sphinxbuild = shutil.which(self.sphinxbuild, path=self.env["PATH"])
+            if not sphinxbuild and target != "mandocs":
+                sys.exit(f"Error: {self.sphinxbuild} not found in PATH.\n")
+
+        if target == "pdfdocs":
+            if not self.pdflatex_cmd and not self.latexmk_cmd:
+                sys.exit("Error: pdflatex or latexmk required for PDF generation")
+
+        docs_dir = os.path.abspath(os.path.join(self.srctree, "Documentation"))
+
+        #
+        # Fill in base arguments for Sphinx build
+        #
+        kerneldoc = self.kerneldoc
+        if kerneldoc.startswith(self.srctree):
+            kerneldoc = os.path.relpath(kerneldoc, self.srctree)
+
+        args = [ "-b", builder, "-c", docs_dir ]
+
+        if builder == "latex":
+            if not paper:
+                paper = PAPER[1]
+
+            args.extend(["-D", f"latex_elements.papersize={paper}paper"])
+
+        if rustdoc:
+            args.extend(["-t", "rustdoc"])
+
+        if not sphinxdirs:
+            sphinxdirs = os.environ.get("SPHINXDIRS", ".")
+
+        #
+        # The sphinx-build tool has a bug: internally, it tries to set
+        # locale with locale.setlocale(locale.LC_ALL, ''). This causes a
+        # crash if language is not set. Detect and fix it.
+        #
+        try:
+            locale.setlocale(locale.LC_ALL, '')
+        except locale.Error:
+            self.env["LC_ALL"] = "C"
+
+        #
+        # sphinxdirs can be a list or a whitespace-separated string
+        #
+        sphinxdirs_list = []
+        for sphinxdir in sphinxdirs:
+            if isinstance(sphinxdir, list):
+                sphinxdirs_list += sphinxdir
+            else:
+                sphinxdirs_list += sphinxdir.split()
+
+        #
+        # Step 1:  Build each directory in separate.
+        #
+        # This is not the best way of handling it, as cross-references between
+        # them will be broken, but this is what we've been doing since
+        # the beginning.
+        #
+        output_dirs = []
+        for sphinxdir in sphinxdirs_list:
+            src_dir = os.path.join(docs_dir, sphinxdir)
+            doctree_dir = os.path.join(self.builddir, ".doctrees")
+            output_dir = os.path.join(self.builddir, sphinxdir, out_dir)
+
+            #
+            # Make directory names canonical
+            #
+            src_dir = os.path.normpath(src_dir)
+            doctree_dir = os.path.normpath(doctree_dir)
+            output_dir = os.path.normpath(output_dir)
+
+            os.makedirs(doctree_dir, exist_ok=True)
+            os.makedirs(output_dir, exist_ok=True)
+
+            output_dirs.append(output_dir)
+
+            build_args = args + [
+                "-d", doctree_dir,
+                "-D", f"kerneldoc_bin={kerneldoc}",
+                "-D", f"version={self.kernelversion}",
+                "-D", f"release={self.kernelrelease}",
+                "-D", f"kerneldoc_srctree={self.srctree}",
+                src_dir,
+                output_dir,
+            ]
+
+            if target == "mandocs":
+                self.handle_man(kerneldoc, docs_dir, src_dir, output_dir)
+            elif not skip_sphinx:
+                try:
+                    result = self.run_sphinx(sphinxbuild, build_args,
+                                             env=self.env)
+
+                    if result:
+                        sys.exit(f"Build failed: return code: {result}")
+
+                except (OSError, ValueError, subprocess.SubprocessError) as e:
+                    sys.exit(f"Build failed: {repr(e)}")
+
+            #
+            # Ensure that each html/epub output will have needed static files
+            #
+            if target in ["htmldocs", "epubdocs"]:
+                self.handle_html(css, output_dir, rustdoc)
+
+        #
+        # Step 2: Some targets (PDF and info) require an extra step once
+        #         sphinx-build finishes
+        #
+        if target == "pdfdocs":
+            self.handle_pdf(output_dirs, deny_vf)
+        elif target == "infodocs":
+            self.handle_info(output_dirs)
+
+def jobs_type(value):
+    """
+    Handle valid values for -j. Accepts Sphinx "-jauto", plus a number
+    equal or bigger than one.
+    """
+    if value is None:
+        return None
+
+    if value.lower() == 'auto':
+        return value.lower()
+
+    try:
+        if int(value) >= 1:
+            return value
+
+        raise argparse.ArgumentTypeError(f"Minimum jobs is 1, got {value}")
+    except ValueError:
+        raise argparse.ArgumentTypeError(f"Must be 'auto' or positive integer, got {value}")  # pylint: disable=W0707
+
+def main():
+    """
+    Main function. The only mandatory argument is the target. If not
+    specified, the other arguments will use default values if not
+    specified at os.environ.
+    """
+    parser = argparse.ArgumentParser(description="Kernel documentation builder")
+
+    parser.add_argument("target", choices=list(TARGETS.keys()),
+                        help="Documentation target to build")
+    parser.add_argument("--sphinxdirs", nargs="+",
+                        help="Specific directories to build")
+    parser.add_argument("--builddir", default="output",
+                        help="Sphinx configuration file")
+
+    parser.add_argument("--theme", help="Sphinx theme to use")
+
+    parser.add_argument("--css", help="Custom CSS file for HTML/EPUB")
+
+    parser.add_argument("--paper", choices=PAPER, default=PAPER[0],
+                        help="Paper size for LaTeX/PDF output")
+
+    parser.add_argument('--deny-vf',
+                        help="Configuration to deny variable fonts on pdf builds")
+
+    parser.add_argument('--rustdoc', action="store_true",
+                        help="Enable rustdoc build. Requires CONFIG_RUST")
+
+    parser.add_argument("-v", "--verbose", action='store_true',
+                        help="place build in verbose mode")
+
+    parser.add_argument('-j', '--jobs', type=jobs_type,
+                        help="Sets number of jobs to use with sphinx-build")
+
+    parser.add_argument('-i', '--interactive', action='store_true',
+                        help="Change latex default to run in interactive mode")
+
+    parser.add_argument('-s', '--skip-sphinx-build', action='store_true',
+                        help="Skip sphinx-build step")
+
+    parser.add_argument("-V", "--venv", nargs='?', const=f'{VENV_DEFAULT}',
+                        default=None,
+                        help=f'If used, run Sphinx from a venv dir (default dir: {VENV_DEFAULT})')
+
+    args = parser.parse_args()
+
+    PythonVersion.check_python(MIN_PYTHON_VERSION, show_alternatives=True,
+                               bail_out=True)
+
+    builder = SphinxBuilder(builddir=args.builddir, venv=args.venv,
+                            verbose=args.verbose, n_jobs=args.jobs,
+                            interactive=args.interactive)
+
+    builder.build(args.target, sphinxdirs=args.sphinxdirs,
+                  theme=args.theme, css=args.css, paper=args.paper,
+                  rustdoc=args.rustdoc, deny_vf=args.deny_vf,
+                  skip_sphinx=args.skip_sphinx_build)
+
+if __name__ == "__main__":
+    main()