docs: Move ja_JP/howto.rst to ja_JP/process/howto.rst

Let Japanese translation of howto.rst in the language drop-down list
by moving it to the expected place.

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Tsugikazu Shibata <shibata@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <b175c52f-34ee-4753-b172-e57fee6fcc30@gmail.com>

docs/ja_JP/index: update section title in Japanese

Update section title "Japanese Translation" in Japanese.
This change is to keep consistency with other translations.

Signed-off-by: Kosuke Fujimoto <fujimotokosuke0@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Tsugikazu Shibata <shibata@linuxfoundation.org>
Cc: Akira Yokosawa <akiyks@gmail.com>
Cc: linux-doc@vger.kernel.org
Reviewed-by: Akira Yokosawa <akiyks@gmail.com>
Link: https://lore.kernel.org/r/20220425124853.8347-1-fujimotokosuke0@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

docs/translations: Skip CJK contents if suitable fonts not found

On systems without "Noto Sans CJK" fonts, CJK chapters in
translations.pdf are full of "TOFU" boxes, with a long build time and
a large log file containing lots of missing-font warnings.

Avoid such waste of time and resources by skipping CJK chapters when
CJK fonts are not available.

To skip whole chapters, change the definition of
\kerneldocBegin{SC|TC|KR|JP} commands so that they can have an argument
to be ignored.
This works as far as the argument (#1) is not used in the command.
In place of skipped contents, put a note on skipped contents at the
beginning of the PDF.

Change the call sites in index.rst of CJK translations accordingly.

When CJK fonts are available, existing command definitions with
no argument just work. LaTeX engine will see additional pairs of
"{" and "}", which add a level of grouping without having any effect
on typesetting.

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/3359ca41-b81d-b2c7-e437-7618efbe241d@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

docs: pdfdocs: Add CJK-language-specific font settings

zh_TW, ko_KR, and ja_JP translations have their preferred glyph sets
different from that of zh_CN.

To switch CJK font in the middle of the translations, introduce custom
LaTeX macros listed below:

\kerneldocBeginSC
\kerneldocEndSC
\kerneldocBeginTC
\kerneldocEndTC
\kerneldocBeginKR
\kerneldocEndKR
\kerneldocBeginJP
\kerneldocEndJP

, and embed a pair of macros in each language's index.rst.

NOTE 1: Update of zh_TW/index.rst is deferred to a follow-up change.

NOTE 2: Custom macros added here do not imply \kerneldocCJK(on|off).
This is intentional. For example, \kerneldocCJKoff needs to be
at the top of Italian translations' index.rst for the footer of
final zh_TW page to be properly typeset.

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Link: https://lore.kernel.org/r/31906baf-7490-68cd-7153-4e4d320fb9b0@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

docs: Activate exCJK only in CJK chapters

Activating xeCJK in English and Italian-translation documents
results in sub-optimal typesetting with wide-looking apostrophes
and quotation marks.

The xeCJK package provides macros for enabling and disabling its
effect in the middle of a document, namely \makexeCJKactive and
\makexeCJKinactive.

So the goal of this change is to activate xeCJK in the relevant
chapters in translations.

To do this:

o Define custom macros in the preamble depending on the
availability of the "Noto Sans CJK" font so that those
macros can be used regardless of the use of xeCJK package.

o Patch \sphinxtableofcontents so that xeCJK is inactivated
after table of contents.

o Embed those custom macros in each language's index.rst file
as a ".. raw:: latex" construct.

Note: A CJK chapter needs \kerneldocCJKon in front of its chapter
heading, while a non-CJK chapter should have \kerneldocCJKoff
below its chapter heading.

This is to make sure the CJK font is available to CJK chapter's
heading and ending page's footer.

Tested against Sphinx versions 2.4.4 and 4.0.2.

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Tested-by: Wu XiangCheng <bobwxc@email.cn>
Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/lkml/2061da0a-6ab1-35f3-99c1-dbc415444f37@gmail.com
Link: https://lore.kernel.org/r/83208ddc-5de9-b283-3fd6-92c635348ca0@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation: Add HOWTO Japanese translation into rst based build system

This commit adds Japanese translation of HOWTO document into rst based
documentation build system with updates.

Signed-off-by: Tsugikazu Shibata <tshibata@ab.jp.nec.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>