linux-kernel - [PATCH 1/3] vt: add modifier support to cursor keys

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Message-ID: <20260203045457.1049793-2-nico@fluxnic.net>
Date: Mon,  2 Feb 2026 23:52:46 -0500
From: Nicolas Pitre <nico@...xnic.net>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>,
	Alexey Gladkov <legion@...nel.org>
Cc: Nicolas Pitre <npitre@...libre.com>,
	linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] vt: add modifier support to cursor keys

From: Nicolas Pitre <npitre@...libre.com>

Generate xterm-style CSI sequences with modifier parameters for arrow
keys when Shift, Alt, or Ctrl are held. For example, Shift+Up produces
ESC [ 1 ; 2 A instead of plain ESC [ A.

The modifier encoding follows the standard xterm convention:
  mod = 1 + (shift ? 1 : 0) + (alt ? 2 : 0) + (ctrl ? 4 : 0)

When no modifiers are pressed, the original behavior is preserved.

Explicit keymap bindings for modified cursor keys (e.g., "shift keycode
103 = Find") take precedence over this automatic modifier encoding.

Signed-off-by: Nicolas Pitre <npitre@...libre.com>
---
 drivers/tty/vt/keyboard.c | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
index d65fc60dd7be..dacc2267de6b 100644
--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -765,14 +765,39 @@ static void k_fn(struct vc_data *vc, unsigned char value, char up_flag)
 		pr_err("k_fn called with value=%d\n", value);
 }
 
+/*
+ * Compute xterm-style modifier parameter for CSI sequences.
+ * Returns 1 + (shift ? 1 : 0) + (alt ? 2 : 0) + (ctrl ? 4 : 0)
+ */
+static int csi_modifier_param(void)
+{
+	int mod = 1;
+
+	if (shift_state & (BIT(KG_SHIFT) | BIT(KG_SHIFTL) | BIT(KG_SHIFTR)))
+		mod += 1;
+	if (shift_state & (BIT(KG_ALT) | BIT(KG_ALTGR)))
+		mod += 2;
+	if (shift_state & (BIT(KG_CTRL) | BIT(KG_CTRLL) | BIT(KG_CTRLR)))
+		mod += 4;
+	return mod;
+}
+
 static void k_cur(struct vc_data *vc, unsigned char value, char up_flag)
 {
 	static const char cur_chars[] = "BDCA";
+	int mod;
 
 	if (up_flag)
 		return;
 
-	applkey(vc, cur_chars[value], vc_kbd_mode(kbd, VC_CKMODE));
+	mod = csi_modifier_param();
+	if (mod > 1) {
+		char buf[] = { 0x1b, '[', '1', ';', '0' + mod, cur_chars[value], 0x00 };
+
+		puts_queue(vc, buf);
+	} else {
+		applkey(vc, cur_chars[value], vc_kbd_mode(kbd, VC_CKMODE));
+	}
 }
 
 static void k_pad(struct vc_data *vc, unsigned char value, char up_flag)
-- 
2.52.0