linux-kernel - [PATCH 2/2] s390/sclp_vt220: convert newlines to CRLF instead of LFCR

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Message-Id: <20241014-s390-kunit-v1-2-941defa765a6@linutronix.de>
Date: Mon, 14 Oct 2024 07:50:07 +0200
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>, 
 Alexander Gordeev <agordeev@...ux.ibm.com>, 
 Christian Borntraeger <borntraeger@...ux.ibm.com>, 
 Sven Schnelle <svens@...ux.ibm.com>, 
 "Guilherme G. Piccoli" <gpiccoli@...lia.com>
Cc: linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>, 
 stable@...r.kernel.org
Subject: [PATCH 2/2] s390/sclp_vt220: convert newlines to CRLF instead of
 LFCR

According to the VT220 specification the possible character combinations
sent on RETURN are only CR or CRLF [0].

	The Return key sends either a CR character (0/13) or a CR
	character (0/13) and an LF character (0/10), depending on the
	set/reset state of line feed/new line mode (LNM).

The sclip/vt220 driver however uses LFCR. This can confuse tools, for
example the kunit runner.

Link: https://vt100.net/docs/vt220-rm/chapter3.html#S3.2
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@...r.kernel.org
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>

---

I'm not entirely sure that SCLP is meant to follow the VT220 standard
here. The only other reference observation I found is the QEMU code and
they are doing "what Linux does".
It would also be possible to hack around this in the kunit runner.
---
 drivers/s390/char/sclp_vt220.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/char/sclp_vt220.c b/drivers/s390/char/sclp_vt220.c
index 218ae604f737ff9e20764ebce857ce427e4a7c44..33b9c968dbcba6584015d70a8500f9f5f70227db 100644
--- a/drivers/s390/char/sclp_vt220.c
+++ b/drivers/s390/char/sclp_vt220.c
@@ -319,7 +319,7 @@ sclp_vt220_add_msg(struct sclp_vt220_request *request,
 	buffer = (void *) ((addr_t) sccb + sccb->header.length);

 	if (convertlf) {
-		/* Perform Linefeed conversion (0x0a -> 0x0a 0x0d)*/
+		/* Perform Linefeed conversion (0x0a -> 0x0d 0x0a)*/
 		for (from=0, to=0;
 		     (from < count) && (to < sclp_vt220_space_left(request));
 		     from++) {
@@ -328,8 +328,8 @@ sclp_vt220_add_msg(struct sclp_vt220_request *request,
 			/* Perform conversion */
 			if (c == 0x0a) {
 				if (to + 1 < sclp_vt220_space_left(request)) {
-					((unsigned char *) buffer)[to++] = c;
 					((unsigned char *) buffer)[to++] = 0x0d;
+					((unsigned char *) buffer)[to++] = c;
 				} else
 					break;

-- 
2.47.0