kernel-doc: don't let V=1 change outcome

The kernel-doc script currently reports a number of issues
only in "verbose" mode, but that's initialized from V=1
(via KBUILD_VERBOSE), so if you use KDOC_WERROR=1 then
adding V=1 might actually break the build. This is rather
unexpected.

Change kernel-doc to not change its behaviour wrt. errors
(or warnings) when verbose mode is enabled, but rather add
separate warning flags (and -Wall) for it. Allow enabling
those flags via environment/make variables in the kernel's
build system for easier user use, but to not have to parse
them in the script itself.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Author: jmberg-intel

Documentation/kbuild/kbuild.rst

@@ -150,6 +150,12 @@ the UTS_MACHINE variable, and on some architectures also the kernel config.
 The value of KBUILD_DEBARCH is assumed (not checked) to be a valid Debian
 architecture.
 
+KDOCFLAGS
+---------
+Specify extra (warning/error) flags for kernel-doc checks during the build,
+see scripts/kernel-doc for which flags are supported. Note that this doesn't
+(currently) apply to documentation builds.
+
 ARCH
 ----
 Set ARCH to the architecture to be built.

scripts/Makefile.build

@@ -101,7 +101,7 @@ else ifeq ($(KBUILD_CHECKSRC),2)
 endif
 
 ifneq ($(KBUILD_EXTRA_WARN),)
-  cmd_checkdoc = $(srctree)/scripts/kernel-doc -none $<
+  cmd_checkdoc = $(srctree)/scripts/kernel-doc -none $(KDOCFLAGS) $<
 endif
 
 # Compile C sources (.c)

scripts/kernel-doc

@@ -23,7 +23,7 @@ kernel-doc - Print formatted kernel documentation to stdout
 
 =head1 SYNOPSIS
 
- kernel-doc [-h] [-v] [-Werror]
+ kernel-doc [-h] [-v] [-Werror] [-Wall] [-Wreturn] [-Wshort-description] [-Wcontents-before-sections]
    [ -man |
      -rst [-sphinx-version VERSION] [-enable-lineno] |
      -none
@@ -133,6 +133,9 @@ my $dohighlight = "";
 
 my $verbose = 0;
 my $Werror = 0;
+my $Wreturn = 0;
+my $Wshort_desc = 0;
+my $Wcontents_before_sections = 0;
 my $output_mode = "rst";
 my $output_preformatted = 0;
 my $no_doc_sections = 0;
@@ -187,9 +190,14 @@ if (defined($ENV{'KCFLAGS'})) {
 	}
 }
 
+# reading this variable is for backwards compat just in case
+# someone was calling it with the variable from outside the
+# kernel's build system
 if (defined($ENV{'KDOC_WERROR'})) {
 	$Werror = "$ENV{'KDOC_WERROR'}";
 }
+# other environment variables are converted to command-line
+# arguments in cmd_checkdoc in the build system
 
 # Generated docbook code is inserted in a template at a point where
 # docbook v3.1 requires a non-zero sequence of RefEntry's; see:
@@ -318,6 +326,16 @@ while ($ARGV[0] =~ m/^--?(.*)/) {
 	$verbose = 1;
     } elsif ($cmd eq "Werror") {
 	$Werror = 1;
+    } elsif ($cmd eq "Wreturn") {
+	$Wreturn = 1;
+    } elsif ($cmd eq "Wshort-desc") {
+	$Wshort_desc = 1;
+    } elsif ($cmd eq "Wcontents-before-sections") {
+	$Wcontents_before_sections = 1;
+    } elsif ($cmd eq "Wall") {
+        $Wreturn = 1;
+        $Wshort_desc = 1;
+        $Wcontents_before_sections = 1;
     } elsif (($cmd eq "h") || ($cmd eq "help")) {
 		pod2usage(-exitval => 0, -verbose => 2);
     } elsif ($cmd eq 'no-doc-sections') {
@@ -1748,9 +1766,9 @@ sub dump_function($$) {
     # This check emits a lot of warnings at the moment, because many
     # functions don't have a 'Return' doc section. So until the number
     # of warnings goes sufficiently down, the check is only performed in
-    # verbose mode.
+    # -Wreturn mode.
     # TODO: always perform the check.
-    if ($verbose && !$noret) {
+    if ($Wreturn && !$noret) {
 	    check_return_section($file, $declaration_name, $return_type);
     }
 
@@ -2054,7 +2072,7 @@ sub process_name($$) {
 	    $state = STATE_NORMAL;
 	}
 
-	if (($declaration_purpose eq "") && $verbose) {
+	if (($declaration_purpose eq "") && $Wshort_desc) {
 	    emit_warning("${file}:$.", "missing initial short description on line:\n$_");
 	}
 
@@ -2103,7 +2121,7 @@ sub process_body($$) {
 	}
 
 	if (($contents ne "") && ($contents ne "\n")) {
-	    if (!$in_doc_sect && $verbose) {
+	    if (!$in_doc_sect && $Wcontents_before_sections) {
 		emit_warning("${file}:$.", "contents before sections\n");
 	    }
 	    dump_section($file, $section, $contents);