From fa6e846f31bb4e1ca0093c707bd2d2080526939c Mon Sep 17 00:00:00 2001
From: =?utf8?q?Imre=20Vad=C3=A1sz?= <imre@vdsz.com>
Date: Wed, 11 Nov 2015 21:53:03 +0100
Subject: [PATCH] syscons: Keep screen content and cursor pos when switching to
 kms console.

---
 sys/dev/misc/syscons/schistory.c | 21 +++++++++++++++++++--
 sys/dev/misc/syscons/scvidctl.c  | 12 ++++++++++++
 sys/dev/misc/syscons/syscons.h   |  1 +
 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/sys/dev/misc/syscons/schistory.c b/sys/dev/misc/syscons/schistory.c
index dbd0291c9f..d75f32b663 100644
--- a/sys/dev/misc/syscons/schistory.c
+++ b/sys/dev/misc/syscons/schistory.c
@@ -66,6 +66,7 @@ static int		extra_history_size
 /* local functions */
 static void copy_history(sc_vtb_t *from, sc_vtb_t *to);
 static void history_to_screen(scr_stat *scp);
+static void history_to_screen_lines(scr_stat *scp, int cnt);
 
 /* allocate a history buffer */
 int
@@ -219,15 +220,23 @@ sc_hist_restore(scr_stat *scp)
 /* copy screen-full of saved lines */
 static void
 history_to_screen(scr_stat *scp)
+{
+	history_to_screen_lines(scp, scp->ysize);
+}
+
+/* copy cnt of saved lines */
+static void
+history_to_screen_lines(scr_stat *scp, int cnt)
 {
 	int pos;
 	int i;
+	int lines = imin(cnt, scp->ysize);
 
 	pos = scp->history_pos;
-	for (i = 1; i <= scp->ysize; ++i) {
+	for (i = 1; i <= lines; ++i) {
 		pos = sc_vtb_pos(scp->history, pos, -scp->xsize);
 		sc_vtb_copy(scp->history, pos,
-			    &scp->vtb, scp->xsize*(scp->ysize - i),
+			    &scp->vtb, scp->xsize*(lines - i),
 			    scp->xsize);
 	}
 	mark_all(scp);
@@ -241,6 +250,14 @@ sc_hist_home(scr_stat *scp)
 	history_to_screen(scp);
 }
 
+/* Restore old_ysize lines from the tail of the history buffer */
+void
+sc_hist_getback(scr_stat *scp, int old_ysize)
+{
+	scp->history_pos = sc_vtb_tail(scp->history);
+	history_to_screen_lines(scp, old_ysize);
+}
+
 /* go to the top of the history buffer */
 void
 sc_hist_end(scr_stat *scp)
diff --git a/sys/dev/misc/syscons/scvidctl.c b/sys/dev/misc/syscons/scvidctl.c
index 58dfcb3f0d..68f07965ec 100644
--- a/sys/dev/misc/syscons/scvidctl.c
+++ b/sys/dev/misc/syscons/scvidctl.c
@@ -762,6 +762,9 @@ sc_update_render(scr_stat *scp)
 	sc_term_sw_t *sw;
 	struct tty *tp;
 	int prev_ysize, new_ysize;
+#ifndef SC_NO_HISTORY
+	int old_xpos, old_ypos;
+#endif
 	int error;
 
 	sw = scp->tsw;
@@ -793,7 +796,12 @@ sc_update_render(scr_stat *scp)
 		}
 		new_ysize = 0;
 #ifndef SC_NO_HISTORY
+		old_xpos = old_ypos = 0;
 		if (scp->history != NULL) {
+			if (scp->xsize > 0) {
+				old_xpos = scp->xpos;
+				old_ypos = scp->ypos;
+			}
 			sc_hist_save(scp);
 			new_ysize = sc_vtb_rows(scp->history);
 		}
@@ -850,6 +858,10 @@ sc_update_render(scr_stat *scp)
 #endif
 #ifndef SC_NO_HISTORY
 		sc_alloc_history_buffer(scp, new_ysize, prev_ysize, FALSE);
+		if (scp->history != NULL) {
+			sc_hist_getback(scp, prev_ysize);
+			sc_move_cursor(scp, old_xpos, old_ypos);
+		}
 #endif
 		crit_exit();
 		scp->status &= ~UNKNOWN_MODE;
diff --git a/sys/dev/misc/syscons/syscons.h b/sys/dev/misc/syscons/syscons.h
index b05d33d6e1..2137e39bd7 100644
--- a/sys/dev/misc/syscons/syscons.h
+++ b/sys/dev/misc/syscons/syscons.h
@@ -537,6 +537,7 @@ void		sc_hist_save(scr_stat *scp);
 		sc_vtb_append(&(scp)->vtb, (from), (scp)->history, (scp)->xsize)
 int		sc_hist_restore(scr_stat *scp);
 void		sc_hist_home(scr_stat *scp);
+void		sc_hist_getback(scr_stat *scp, int old_ysize);
 void		sc_hist_end(scr_stat *scp);
 int		sc_hist_up_line(scr_stat *scp);
 int		sc_hist_down_line(scr_stat *scp);
-- 
2.41.0