[PATCH] checkpatch: warn if changed lines exceeds a maximum size

[Brown, Nicholas]

Changed lines is the total of inserted and deleted lines.
By default there is no limit, --max-changed-lines may be used to set a
value. Some users may wish to encourage that patches are split into
smaller parts using this.
See Documentation/process/submitting-patches.rst#split-changes

Signed-off-by: Nicholas Brown <nick.brown@xxxxxxx>
---
 scripts/checkpatch.pl | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 31031f10fe56..1217d782b6bb 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -49,6 +49,7 @@ my @ignore = ();
 my $help = 0;
 my $configuration_file = ".checkpatch.conf";
 my $max_line_length = 80;
+my $max_changed_lines; # undef = no max
 my $ignore_perl_version = 0;
 my $minimum_perl_version = 5.10.0;
 my $min_conf_desc_length = 4;
@@ -209,6 +210,7 @@ GetOptions(
 	'show-types!'	=> \$show_types,
 	'list-types!'	=> \$list_types,
 	'max-line-length=i' => \$max_line_length,
+	'max-changed-lines=i' => \$max_changed_lines,
 	'min-conf-desc-length=i' => \$min_conf_desc_length,
 	'root=s'	=> \$root,
 	'summary!'	=> \$summary,
@@ -2165,6 +2167,8 @@ sub process {
 	my $filename = shift;
 
 	my $linenr=0;
+	my $inserted_lines_total=0;
+	my $deleted_lines_total=0;
 	my $prevline="";
 	my $prevrawline="";
 	my $stashline="";
@@ -2233,6 +2237,14 @@ sub process {
 
 		push(@fixed, $rawline) if ($fix);
 
+		if ($rawline=~/^\+/) {
+		  $inserted_lines_total++
+		}
+
+		if ($rawline=~/^-/) {
+		  $deleted_lines_total++
+		}
+
 		if ($rawline=~/^\+\+\+\s+(\S+)/) {
 			$setup_docs = 0;
 			if ($1 =~ m@Documentation/admin-guide/kernel-parameters.rst$@) {
@@ -2306,6 +2318,11 @@ sub process {
 
 	$prefix = '';
 
+	if (defined $max_changed_lines &&
+	    ($inserted_lines_total+$deleted_lines_total > $max_changed_lines)) {
+	  WARN("MAX_CHANGED_LINES", "please split the change into smaller parts\n");
+	}
+
 	$realcnt = 0;
 	$linenr = 0;
 	$fixlinenr = -1;
-- 
2.14.1