From b53fe14843ab1d5fc73d3e0ae2b14c182c6ee577 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bojan=20Novkovi=C4=87?= <bojan.novkovic@fer.hr>
Date: Sat, 7 Oct 2023 20:59:57 +0300
Subject: [PATCH] (s)tty: add support for IUTF8 input flag

This patch adds the necessary kernel and stty code to support setting
the IUTF8 flag for ttys. It is the first of two patches that fix
backspace behaviour for UTF-8 encoded characters when in canonical mode.

Reported by:	christos
Reviewed by:	christos, imp
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D42066

(cherry picked from commit 128f63cedc14ae21b35f74e11e2fe1a5659c58e8)
---
 bin/stty/modes.c         | 2 ++
 bin/stty/print.c         | 1 +
 bin/stty/stty.1          | 3 +++
 share/man/man4/termios.4 | 2 ++
 sys/kern/tty.c           | 4 ++--
 sys/sys/_termios.h       | 1 +
 6 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/bin/stty/modes.c b/bin/stty/modes.c
index ce39083d7d6..3818677ddc4 100644
--- a/bin/stty/modes.c
+++ b/bin/stty/modes.c
@@ -126,6 +126,8 @@ static const struct modes imodes[] = {
 	{ "-decctlq",	IXANY, 0 },
 	{ "imaxbel",	IMAXBEL, 0 },
 	{ "-imaxbel",	0, IMAXBEL },
+	{ "iutf8",	IUTF8, 0 },
+	{ "-iutf8",	0, IUTF8 },
 	{ NULL,		0, 0 },
 };
 
diff --git a/bin/stty/print.c b/bin/stty/print.c
index 07a3c205847..33472bbccea 100644
--- a/bin/stty/print.c
+++ b/bin/stty/print.c
@@ -127,6 +127,7 @@ print(struct termios *tp, struct winsize *wp, int ldisc, enum FMT fmt)
 	put("-inpck", INPCK, 0);
 	put("-ignpar", IGNPAR, 0);
 	put("-parmrk", PARMRK, 0);
+	put("-iutf8", IUTF8, 1);
 
 	/* output flags */
 	tmp = tp->c_oflag;
diff --git a/bin/stty/stty.1 b/bin/stty/stty.1
index 9e9405928c6..c572a657a99 100644
--- a/bin/stty/stty.1
+++ b/bin/stty/stty.1
@@ -224,6 +224,9 @@ if
 .Cm imaxbel
 is unset and the input queue is full, the next input character causes
 the entire input and output queues to be discarded.
+.It Cm iutf8 Pq Fl iutf8
+Assume that input characters are UTF-8 encoded. Setting this flag
+causes backspace to properly delete multibyte characters in canonical mode.
 .El
 .Ss Output Modes:
 This corresponds to the c_oflag of the termios structure.
diff --git a/share/man/man4/termios.4 b/share/man/man4/termios.4
index d3a5c8fa582..80015025345 100644
--- a/share/man/man4/termios.4
+++ b/share/man/man4/termios.4
@@ -884,6 +884,8 @@ following masks:
 /* any char will restart after stop */
 .It Dv IMAXBEL
 /* ring bell on input queue full */
+.It Dv IUTF8
+/* assume input is UTF-8 encoded */
 .El
 .Pp
 In the context of asynchronous serial data transmission, a break
diff --git a/sys/kern/tty.c b/sys/kern/tty.c
index 134c1dfba98..62023394741 100644
--- a/sys/kern/tty.c
+++ b/sys/kern/tty.c
@@ -85,8 +85,8 @@ static const char	*dev_console_filename;
 /*
  * Flags that are supported and stored by this implementation.
  */
-#define TTYSUP_IFLAG	(IGNBRK|BRKINT|IGNPAR|PARMRK|INPCK|ISTRIP|\
-			INLCR|IGNCR|ICRNL|IXON|IXOFF|IXANY|IMAXBEL)
+#define TTYSUP_IFLAG	(IGNBRK|BRKINT|IGNPAR|PARMRK|INPCK|ISTRIP|INLCR|\
+			IGNCR|ICRNL|IXON|IXOFF|IXANY|IMAXBEL|IUTF8)
 #define TTYSUP_OFLAG	(OPOST|ONLCR|TAB3|ONOEOT|OCRNL|ONOCR|ONLRET)
 #define TTYSUP_LFLAG	(ECHOKE|ECHOE|ECHOK|ECHO|ECHONL|ECHOPRT|\
 			ECHOCTL|ISIG|ICANON|ALTWERASE|IEXTEN|TOSTOP|\
diff --git a/sys/sys/_termios.h b/sys/sys/_termios.h
index 327ffcb2f98..823752732ee 100644
--- a/sys/sys/_termios.h
+++ b/sys/sys/_termios.h
@@ -97,6 +97,7 @@
 #endif
 #if __BSD_VISIBLE
 #define	IMAXBEL		0x00002000	/* ring bell on input queue full */
+#define IUTF8		0x00004000	/* assume input is utf-8 encoded */
 #endif
 
 /*