scripts/kernel-doc: Adding cross-reference links to html documentation.

Functions, Structs and Parameters definitions on kernel documentation
are pure cosmetic, it only highlights the element.

To ease the navigation in the documentation we should use <links> inside
those tags so readers can easily jump between methods directly.

This was discussed in 2014[1] and is implemented by getting a list
of <refentries> from the DocBook XML to generate a database. Then it looks
for <function>,<structnames> and <paramdef> tags that matches the ones in
the database. As it only links existent references, no broken links are
added.

[1] - lists.freedesktop.org/archives/dri-devel/2014-August/065404.html
Signed-off-by: Danilo Cesar Lemes de Paula <danilo.cesar@collabora.co.uk>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Stephan Mueller <smueller@chronox.de>
Cc: Michal Marek <mmarek@suse.cz>
Cc: intel-gfx <intel-gfx@lists.freedesktop.org>
Cc: dri-devel <dri-devel@lists.freedesktop.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/DocBook/Makefile

@@ -66,6 +66,7 @@ installmandocs: mandocs
 
 ###
 #External programs used
+KERNELDOCXMLREF = $(srctree)/scripts/kernel-doc-xml-ref
 KERNELDOC       = $(srctree)/scripts/kernel-doc
 DOCPROC         = $(objtree)/scripts/docproc
 
@@ -91,7 +92,7 @@ define rule_docproc
         ) > $(dir $@).$(notdir $@).cmd
 endef
 
-%.xml: %.tmpl $(KERNELDOC) $(DOCPROC) FORCE
+%.xml: %.tmpl $(KERNELDOC) $(DOCPROC) $(KERNELDOCXMLREF) FORCE
 	$(call if_changed_rule,docproc)
 
 # Tell kbuild to always build the programs
@@ -142,7 +143,20 @@ quiet_cmd_db2html = HTML    $@
 		echo '<a HREF="$(patsubst %.html,%,$(notdir $@))/index.html"> \
 		$(patsubst %.html,%,$(notdir $@))</a><p>' > $@
 
-%.html:	%.xml
+###
+# Rules to create an aux XML and .db, and use them to re-process the DocBook XML
+# to fill internal hyperlinks
+       gen_aux_xml = :
+ quiet_gen_aux_xml = echo '  XMLREF  $@'
+silent_gen_aux_xml = :
+%.aux.xml: %.xml
+	@$($(quiet)gen_aux_xml)
+	@rm -rf $@
+	@(cat $< | egrep "^<refentry id" | egrep -o "\".*\"" | cut -f 2 -d \" > $<.db)
+	@$(KERNELDOCXMLREF) -db $<.db $< > $@
+.PRECIOUS: %.aux.xml
+
+%.html:	%.aux.xml
 	@(which xmlto > /dev/null 2>&1) || \
 	 (echo "*** You need to install xmlto ***"; \
 	  exit 1)
@@ -220,6 +234,9 @@ clean-files := $(DOCBOOKS) \
 	$(patsubst %.xml, %.pdf,     $(DOCBOOKS)) \
 	$(patsubst %.xml, %.html,    $(DOCBOOKS)) \
 	$(patsubst %.xml, %.9,       $(DOCBOOKS)) \
+	$(patsubst %.xml, %.aux.xml, $(DOCBOOKS)) \
+	$(patsubst %.xml, %.xml.db,  $(DOCBOOKS)) \
+	$(patsubst %.xml, %.xml,     $(DOCBOOKS)) \
 	$(index)
 
 clean-dirs := $(patsubst %.xml,%,$(DOCBOOKS)) man

scripts/kernel-doc-xml-ref

+#!/usr/bin/perl -w
+
+use strict;
+
+## Copyright (C) 2015  Intel Corporation                         ##
+#                                                                ##
+## This software falls under the GNU General Public License.     ##
+## Please read the COPYING file for more information             ##
+#
+#
+# This software reads a XML file and a list of valid interal
+# references to replace Docbook tags with links.
+#
+# The list of "valid internal references" must be one-per-line in the following format:
+#      API-struct-foo
+#      API-enum-bar
+#      API-my-function
+#
+# The software walks over the XML file looking for xml tags representing possible references
+# to the Document. Each reference will be cross checked against the "Valid Internal Reference" list. If
+# the referece is found it replaces its content by a <link> tag.
+#
+# usage:
+# kernel-doc-xml-ref -db filename
+#		     xml filename > outputfile
+
+# read arguments
+if ($#ARGV != 2) {
+	usage();
+}
+
+#Holds the database filename
+my $databasefile;
+my @database;
+
+#holds the inputfile
+my $inputfile;
+my $errors = 0;
+
+my %highlights = (
+	"<function>(.*?)</function>",
+	    "\"<function>\" . convert_function(\$1, \$line) . \"</function>\"",
+	"<structname>(.*?)</structname>",
+	    "\"<structname>\" . convert_struct(\$1) . \"</structname>\"",
+	"<funcdef>(.*?)<function>(.*?)</function></funcdef>",
+	    "\"<funcdef>\" . convert_param(\$1) . \"<function>\$2</function></funcdef>\"",
+	"<paramdef>(.*?)<parameter>(.*?)</parameter></paramdef>",
+	    "\"<paramdef>\" . convert_param(\$1) . \"<parameter>\$2</parameter></paramdef>\"");
+
+while($ARGV[0] =~ m/^-(.*)/) {
+	my $cmd = shift @ARGV;
+	if ($cmd eq "-db") {
+		$databasefile = shift @ARGV
+	} else {
+		usage();
+	}
+}
+$inputfile = shift @ARGV;
+
+sub open_database {
+	open (my $handle, '<', $databasefile) or die "Cannot open $databasefile";
+	chomp(my @lines = <$handle>);
+	close $handle;
+
+	@database = @lines;
+}
+
+sub process_file {
+	open_database();
+
+	my $dohighlight;
+	foreach my $pattern (keys %highlights) {
+		$dohighlight .=  "\$line =~ s:$pattern:$highlights{$pattern}:eg;\n";
+	}
+
+	open(FILE, $inputfile) or die("Could not open $inputfile") or die ("Cannot open $inputfile");
+	foreach my $line (<FILE>)  {
+		eval $dohighlight;
+		print $line;
+	}
+}
+
+sub trim($_)
+{
+	my $str = $_[0];
+	$str =~ s/^\s+|\s+$//g;
+	return $str
+}
+
+sub has_key_defined($_)
+{
+	if ( grep( /^$_[0]$/, @database)) {
+		return 1;
+	}
+	return 0;
+}
+
+# Gets a <function> content and add it a hyperlink if possible.
+sub convert_function($_)
+{
+	my $arg = $_[0];
+	my $key = $_[0];
+
+	my $line = $_[1];
+
+	$key = trim($key);
+
+	$key =~ s/[^A-Za-z0-9]/-/g;
+	$key = "API-" . $key;
+
+	# We shouldn't add links to <funcdef> prototype
+	if (!has_key_defined($key) || $line =~ m/\s+<funcdef/i) {
+		return $arg;
+	}
+
+	my $head = $arg;
+	my $tail = "";
+	if ($arg =~ /(.*?)( ?)$/) {
+		$head = $1;
+		$tail = $2;
+	}
+	return "<link linkend=\"$key\">$head</link>$tail";
+}
+
+# Converting a struct text to link
+sub convert_struct($_)
+{
+	my $arg = $_[0];
+	my $key = $_[0];
+	$key =~ s/(struct )?(\w)/$2/g;
+	$key =~ s/[^A-Za-z0-9]/-/g;
+	$key = "API-struct-" . $key;
+
+	if (!has_key_defined($key)) {
+		return $arg;
+	}
+
+	my ($head, $tail) = split_pointer($arg);
+	return "<link linkend=\"$key\">$head</link>$tail";
+}
+
+# Identify "object *" elements
+sub split_pointer($_)
+{
+	my $arg = $_[0];
+	if ($arg =~ /(.*?)( ?\* ?)/) {
+		return ($1, $2);
+	}
+	return ($arg, "");
+}
+
+sub convert_param($_)
+{
+	my $type = $_[0];
+	my $keyname = convert_key_name($type);
+
+	if (!has_key_defined($keyname)) {
+		return $type;
+	}
+
+	my ($head, $tail) = split_pointer($type);
+	return "<link linkend=\"$keyname\">$head</link>$tail";
+
+}
+
+# DocBook links are in the API-<TYPE>-<STRUCT-NAME> format
+# This method gets an element and returns a valid DocBook reference for it.
+sub convert_key_name($_)
+{
+	#Pattern $2 is optional and might be uninitialized
+	no warnings 'uninitialized';
+
+	my $str = $_[0];
+	$str =~ s/(const|static)? ?(struct)? ?([a-zA-Z0-9_]+) ?(\*|&)?/$2 $3/g ;
+
+	# trim
+	$str =~ s/^\s+|\s+$//g;
+
+	# spaces and _ to -
+	$str =~ s/[^A-Za-z0-9]/-/g;
+
+	return "API-" . $str;
+}
+
+sub usage {
+	print "Usage: $0 -db database filename\n";
+	print "         xml source file(s) > outputfile\n";
+	exit 1;
+}
+
+# starting point
+process_file();
+
+if ($errors) {
+	print STDERR "$errors errors\n";
+}
+
+exit($errors);