checkpatch: warn when a patch doesn't have a description

Potential patches should have a commit description.  Emit a warning when
there isn't one.

[akpm@linux-foundation.org: s/else if/elsif/]
Link: http://lkml.kernel.org/r/1b099f4d8373aa583a17011992676bf0f3f09eee.camel@perches.com
Signed-off-by: Joe Perches <joe@perches.com>
Suggested-by: Prakruthi Deepak Heragu <pheragu@codeaurora.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -2253,6 +2253,7 @@ sub process {
 	my $in_header_lines = $file ? 0 : 1;
 	my $in_commit_log = 0;		#Scanning lines before patch
 	my $has_commit_log = 0;		#Encountered lines before patch
+	my $commit_log_lines = 0;	#Number of commit log lines
 	my $commit_log_possible_stack_dump = 0;
 	my $commit_log_long_line = 0;
 	my $commit_log_has_diff = 0;
@@ -2510,6 +2511,18 @@ sub process {
 
 		$cnt_lines++ if ($realcnt != 0);
 
+# Verify the existence of a commit log if appropriate
+# 2 is used because a $signature is counted in $commit_log_lines
+		if ($in_commit_log) {
+			if ($line !~ /^\s*$/) {
+				$commit_log_lines++;	#could be a $signature
+			}
+		} elsif ($has_commit_log && $commit_log_lines < 2) {
+			WARN("COMMIT_MESSAGE",
+			     "Missing commit description - Add an appropriate one\n");
+			$commit_log_lines = 2;	#warn only once
+		}
+
 # Check if the commit log has what seems like a diff which can confuse patch
 		if ($in_commit_log && !$commit_log_has_diff &&
 		    (($line =~ m@^\s+diff\b.*a/[\w/]+@ &&