vt: Perform safe console erase only once

Commit f8df13e0a9 ("tty: Clean console safely") added code to clear
both the scrollback buffer and the screen with "\e[3J", then execution
falls through into the code to simply clear the screen. This means
scr_memsetw() and the console driver update callback are called twice
on the whole screen buffer. Let's reorganize the code so the same work
is not performed twice needlessly.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index f97251f..1eb1a37 100644 (file)
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1178,15 +1178,8 @@ static void csi_J(struct vc_data *vc, int vpar)
                        count = ((vc->vc_pos - vc->vc_origin) >> 1) + 1;
                        start = (unsigned short *)vc->vc_origin;
                        break;
-               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);
-                       /* fall through */
                case 2: /* erase whole display */
+               case 3: /* (and scrollback buffer later) */
                        count = vc->vc_cols * vc->vc_rows;
                        start = (unsigned short *)vc->vc_origin;
                        break;
@@ -1194,7 +1187,12 @@ static void csi_J(struct vc_data *vc, int vpar)
                        return;
        }
        scr_memsetw(start, vc->vc_video_erase_char, 2 * count);
-       if (con_should_update(vc))
+       if (vpar == 3) {
+               set_origin(vc);
+               flush_scrollback(vc);
+               if (con_is_visible(vc))
+                       update_screen(vc);
+       } else if (con_should_update(vc))
                do_update_region(vc, (unsigned long) start, count);
        vc->vc_need_wrap = 0;
 }