console: Add callback to flush scrollback buffer to consw struct

This new callback is in preparation for persistent scrollback buffer
support for VGA consoles.
With a single scrollback buffer for all consoles, we could flush the
buffer just by invocating consw->con_switch(). But when each VGA console
has its own scrollback buffer, we need a new callback to tell the
video console driver which buffer to flush.
Signed-off-by: Manuel Schölling <manuel.schoelling@gmx.de>
Reviewed-by: Andrey Utkin <andrey_utkin@fastmail.com>
Tested-by: Andrey Utkin <andrey_utkin@fastmail.com>
Tested-by: Adam Borowski <kilobyte@angband.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/vt/vt.c

@@ -625,6 +625,14 @@ static void save_screen(struct vc_data *vc)
 		vc->vc_sw->con_save_screen(vc);
 }
 
+static void flush_scrollback(struct vc_data *vc)
+{
+	WARN_CONSOLE_UNLOCKED();
+
+	if (vc->vc_sw->con_flush_scrollback)
+		vc->vc_sw->con_flush_scrollback(vc);
+}
+
 /*
  *	Redrawing of screen
  */
@@ -1171,6 +1179,7 @@ static void csi_J(struct vc_data *vc, int vpar)
 		case 3: /* erase scroll-back buffer (and whole display) */
 			scr_memsetw(vc->vc_screenbuf, vc->vc_video_erase_char,
 				    vc->vc_screenbuf_size);
+			flush_scrollback(vc);
 			set_origin(vc);
 			if (con_is_visible(vc))
 				update_screen(vc);

drivers/video/console/vgacon.c

@@ -173,6 +173,16 @@ static struct vgacon_scrollback_info {
 	int restore;
 } vgacon_scrollback;
 
+static void vgacon_scrollback_reset(size_t reset_size)
+{
+	if (vgacon_scrollback.data && reset_size > 0)
+		memset(vgacon_scrollback.data, 0, reset_size);
+
+	vgacon_scrollback.cnt  = 0;
+	vgacon_scrollback.tail = 0;
+	vgacon_scrollback.cur  = 0;
+}
+
 static void vgacon_scrollback_init(int pitch)
 {
 	int rows = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024/pitch;
@@ -305,6 +315,14 @@ static void vgacon_scrolldelta(struct vc_data *c, int lines)
 	} else
 		vgacon_cursor(c, CM_MOVE);
 }
+
+static void vgacon_flush_scrollback(struct vc_data *c)
+{
+	size_t size = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024;
+
+	if (c->vc_num == fg_console)
+		vgacon_scrollback_reset(size);
+}
 #else
 #define vgacon_scrollback_startup(...) do { } while (0)
 #define vgacon_scrollback_init(...)    do { } while (0)
@@ -322,6 +340,10 @@ static void vgacon_scrolldelta(struct vc_data *c, int lines)
 			vga_vram_size);
 	vga_set_mem_top(c);
 }
+
+static void vgacon_flush_scrollback(struct vc_data *c)
+{
+}
 #endif /* CONFIG_VGACON_SOFT_SCROLLBACK */
 
 static const char *vgacon_startup(void)
@@ -1329,7 +1351,6 @@ static bool vgacon_scroll(struct vc_data *c, unsigned int t, unsigned int b,
 	return true;
 }
 
-
 /*
  *  The console `switch' structure for the VGA based console
  */
@@ -1362,6 +1383,7 @@ const struct consw vga_con = {
 	.con_save_screen = vgacon_save_screen,
 	.con_build_attr = vgacon_build_attr,
 	.con_invert_region = vgacon_invert_region,
+	.con_flush_scrollback = vgacon_flush_scrollback,
 };
 EXPORT_SYMBOL(vga_con);
 

include/linux/console.h

@@ -72,6 +72,10 @@ struct consw {
 	void	(*con_invert_region)(struct vc_data *, u16 *, int);
 	u16    *(*con_screen_pos)(struct vc_data *, int);
 	unsigned long (*con_getxy)(struct vc_data *, unsigned long, int *, int *);
+	/*
+	 * Flush the video console driver's scrollback buffer
+	 */
+	void	(*con_flush_scrollback)(struct vc_data *);
 	/*
 	 * Prepare the console for the debugger.  This includes, but is not
 	 * limited to, unblanking the console, loading an appropriate