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From:   Nicolas Pitre <nicolas.pitre@linaro.org>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Dave Mielke <Dave@mielke.cc>, linux-kernel@vger.kernel.org
Subject: [PATCH 1/6] vt: make vt_console_print() compatible with the unicode screen buffer
Date:   Tue,  8 Jan 2019 22:54:59 -0500
Message-Id: <20190109035504.8413-2-nicolas.pitre@linaro.org>
In-Reply-To: <20190109035504.8413-1-nicolas.pitre@linaro.org>
References: <20190109035504.8413-1-nicolas.pitre@linaro.org>
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Sender: linux-kernel-owner@vger.kernel.org
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When kernel messages are printed to the console, they appear blank on
the unicode screen. This is because vt_console_print() is lacking a call
to vc_uniscr_putc(). However the later function assumes vc->vc_x is
always up to date when called, which is not the case here as
vt_console_print() uses it to mark the beginning of the display update.

This patch reworks (and simplifies) vt_console_print() so that vc->vc_x
is always valid and keeps the start of display update in a local variable
instead, which finally allows for adding the missing vc_uniscr_putc()
call.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Cc: stable@vger.kernel.org # v4.19+
---
 drivers/tty/vt/vt.c | 47 +++++++++++++++------------------------------
 1 file changed, 15 insertions(+), 32 deletions(-)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 41ec8e5010..b9004bd087 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -2884,8 +2884,7 @@ static void vt_console_print(struct console *co, co=
nst char *b, unsigned count)
 	unsigned char c;
 	static DEFINE_SPINLOCK(printing_lock);
 	const ushort *start;
-	ushort cnt =3D 0;
-	ushort myx;
+	ushort start_x, cnt;
 	int kmsg_console;
=20
 	/* console busy or not yet initialized */
@@ -2898,10 +2897,6 @@ static void vt_console_print(struct console *co, c=
onst char *b, unsigned count)
 	if (kmsg_console && vc_cons_allocated(kmsg_console - 1))
 		vc =3D vc_cons[kmsg_console - 1].d;
=20
-	/* read `x' only after setting currcons properly (otherwise
-	   the `x' macro will read the x of the foreground console). */
-	myx =3D vc->vc_x;
-
 	if (!vc_cons_allocated(fg_console)) {
 		/* impossible */
 		/* printk("vt_console_print: tty %d not allocated ??\n", currcons+1); =
*/
@@ -2916,53 +2911,41 @@ static void vt_console_print(struct console *co, =
const char *b, unsigned count)
 		hide_cursor(vc);
=20
 	start =3D (ushort *)vc->vc_pos;
-
-	/* Contrived structure to try to emulate original need_wrap behaviour
-	 * Problems caused when we have need_wrap set on '\n' character */
+	start_x =3D vc->vc_x;
+	cnt =3D 0;
 	while (count--) {
 		c =3D *b++;
 		if (c =3D=3D 10 || c =3D=3D 13 || c =3D=3D 8 || vc->vc_need_wrap) {
-			if (cnt > 0) {
-				if (con_is_visible(vc))
-					vc->vc_sw->con_putcs(vc, start, cnt, vc->vc_y, vc->vc_x);
-				vc->vc_x +=3D cnt;
-				if (vc->vc_need_wrap)
-					vc->vc_x--;
-				cnt =3D 0;
-			}
+			if (cnt && con_is_visible(vc))
+				vc->vc_sw->con_putcs(vc, start, cnt, vc->vc_y, start_x);
+			cnt =3D 0;
 			if (c =3D=3D 8) {		/* backspace */
 				bs(vc);
 				start =3D (ushort *)vc->vc_pos;
-				myx =3D vc->vc_x;
+				start_x =3D vc->vc_x;
 				continue;
 			}
 			if (c !=3D 13)
 				lf(vc);
 			cr(vc);
 			start =3D (ushort *)vc->vc_pos;
-			myx =3D vc->vc_x;
+			start_x =3D vc->vc_x;
 			if (c =3D=3D 10 || c =3D=3D 13)
 				continue;
 		}
+		vc_uniscr_putc(vc, c);
 		scr_writew((vc->vc_attr << 8) + c, (unsigned short *)vc->vc_pos);
 		notify_write(vc, c);
 		cnt++;
-		if (myx =3D=3D vc->vc_cols - 1) {
-			vc->vc_need_wrap =3D 1;
-			continue;
-		}
-		vc->vc_pos +=3D 2;
-		myx++;
-	}
-	if (cnt > 0) {
-		if (con_is_visible(vc))
-			vc->vc_sw->con_putcs(vc, start, cnt, vc->vc_y, vc->vc_x);
-		vc->vc_x +=3D cnt;
-		if (vc->vc_x =3D=3D vc->vc_cols) {
-			vc->vc_x--;
+		if (vc->vc_x =3D=3D vc->vc_cols - 1) {
 			vc->vc_need_wrap =3D 1;
+		} else {
+			vc->vc_pos +=3D 2;
+			vc->vc_x++;
 		}
 	}
+	if (cnt && con_is_visible(vc))
+		vc->vc_sw->con_putcs(vc, start, cnt, vc->vc_y, start_x);
 	set_cursor(vc);
 	notify_update(vc);
=20
--=20
2.20.1