[PATCH 4/4] n_tty: wrap all OLCUC code in a config option

[Adam Borowski]

Setting it to N, beside dropping runes, also disables old-style support
for all-caps OLCUC.  To get those 40 years old terminals to work, set
CONFIG_TTY_RUNES=y which will DTRT when stty iutf8 is off.

Signed-off-by: Adam Borowski <kilobyte@xxxxxxxxxx>
---
 drivers/tty/Kconfig | 17 +++++++++++++++++
 drivers/tty/n_tty.c | 10 ++++++++++
 2 files changed, 27 insertions(+)

diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
index 95103054c0e4..cfeed2b196e5 100644
--- a/drivers/tty/Kconfig
+++ b/drivers/tty/Kconfig
@@ -151,6 +151,23 @@ config LEGACY_PTY_COUNT
 	  When not in use, each legacy PTY occupies 12 bytes on 32-bit
 	  architectures and 24 bytes on 64-bit architectures.
 
+config TTY_RUNES
+	bool "Runes on OLCUC"
+	default y
+	---help---
+	  Certain terminals from the days of Unix' infancy supported only
+	  all-caps, so-called "Great Runes".  Linux still has rudimentary
+	  support for those, although how can you connect one is another
+	  matter; you enable that via "stty olcuc".
+
+	  On anything modern, though (as in "stty iutf8"), you do get actual
+	  runes.  You need userspace fonts for that; modern distributions
+	  tend to install both raster (xterm/rxvt) and TrueType (most
+	  terminals) fonts on their default GUI setups.  Alas, this is not
+	  the case on console due to sharply limited character sets.
+
+	  C'mon, you know you want to say Y!
+
 config BFIN_JTAG_COMM
 	tristate "Blackfin JTAG Communication"
 	depends on BLACKFIN
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 3b8b745eb7cf..14d090576f09 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -123,7 +123,9 @@ struct n_tty_data {
 	unsigned int column;
 	unsigned int canon_column;
 	size_t echo_tail;
+#ifdef CONFIG_TTY_RUNES
 	unsigned int vt_state;
+#endif
 
 	struct mutex atomic_read_lock;
 	struct mutex output_lock;
@@ -395,6 +397,7 @@ static inline int is_continuation(unsigned char c, struct tty_struct *tty)
 	return I_IUTF8(tty) && is_utf8_continuation(c);
 }
 
+#ifdef CONFIG_TTY_RUNES
 /* process one OLCUC char (possibly partial unicode)
  *
  * We need to partially parse ANSI sequences to avoid uppercasing them;
@@ -475,6 +478,7 @@ static int do_olcuc_char(unsigned char c, struct tty_struct *tty, int space)
 	tty_put_char(tty, c);
 	return 1;
 }
+#endif
 
 /**
  *	do_output_char			-	output one character
@@ -546,8 +550,10 @@ static int do_output_char(unsigned char c, struct tty_struct *tty, int space)
 			ldata->column--;
 		break;
 	default:
+#ifdef CONFIG_TTY_RUNES
 		if (O_OLCUC(tty))
 			return do_olcuc_char(c, tty, space);
+#endif
 		if (!iscntrl(c) && !is_continuation(c, tty))
 			ldata->column++;
 		break;
@@ -650,8 +656,10 @@ static ssize_t process_output_block(struct tty_struct *tty,
 				ldata->column--;
 			break;
 		default:
+#ifdef CONFIG_TTY_RUNES
 			if (O_OLCUC(tty))
 				goto break_out;
+#endif
 			if (!iscntrl(c) && !is_continuation(c, tty))
 				ldata->column++;
 			break;
@@ -1975,7 +1983,9 @@ static int n_tty_open(struct tty_struct *tty)
 	ldata->num_overrun = 0;
 	ldata->no_room = 0;
 	ldata->lnext = 0;
+#ifdef CONFIG_TTY_RUNES
 	ldata->vt_state = ESnormal;
+#endif
 	tty->closing = 0;
 	/* indicate buffer work may resume */
 	clear_bit(TTY_LDISC_HALTED, &tty->flags);
-- 
2.11.0