[PATCH 1/2] checkpatch: Add check item for RFC tags is outside the subject prefix

[Cai Huoqing <caihuoqing@baidu.com>]

Some patches have been sent, the RFC tag of which is
outside the subject prefix is incorrect. like this:
"Subject: [PATCH v2] RFC:"

Perfer "Subject: [RFC PATCH v2]" to "Subject: [PATCH v2] RFC:",
so add check item for it.

Signed-off-by: Cai Huoqing <caihuoqing@baidu.com>
---
 scripts/checkpatch.pl | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index c27d2312cfc3..802f78904247 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -3121,6 +3121,12 @@ sub process {
 			     "A patch subject line should describe the change not the tool that found it\n" . $herecurr);
 		}
 
+# Check if RFC tags is outside the subject prefix
+		if ($in_header_lines && $line =~ /^Subject:.*patch\s*.*]\s*rfc:/i) {
+			WARN("RFC_TAG_PREFIX",
+			     "RFC tag is outside subject prefix, try \"git format-patch --rfc\"\n" . $herecurr);
+		}
+
 # Check for Gerrit Change-Ids not in any patch context
 		if ($realfile eq '' && !$has_patch_separator && $line =~ /^\s*change-id:/i) {
 			if (ERROR("GERRIT_CHANGE_ID",
-- 
2.25.1