linux-kernel - [PATCH] tty: vt: initialize softcursor

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Date:	Sun, 01 Nov 2015 19:48:18 +0100
From:	Melchior FRANZ <mfranz@....at>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	Jiri Slaby <jslaby@...e.com>, linux-kernel@...r.kernel.org,
	Melchior FRANZ <melchior.franz@...zinger.com>
Subject: [PATCH] tty: vt: initialize softcursor_original correctly

add_softcursor() stores the contents of the text buffer position in this
variable before drawing the softcursor, whereas hide_softcursor() writes
the value back. A value of -1 means that no cursor has been drawn and
therefore no character is to be restored. softcursor_original, however,
is only implicitly initialized with 0. Therefore, when hide_softcursor
is called for the first time (console_init -> con_init -> redraw_screen
-> hide_cursor), it wrongly writes 0x0000 in the top left corner of
the text buffer. Normally, this is just as black as the rest of the
screen (vc_video_erase_char) and can't be seen, but it appears as a
black cursor rectangle on non-black backgrounds e.g. with boot option
"vt.global_cursor_default=0 vt.color=0xf0". softcursor_original needs
to be initialized with -1.

Signed-off-by: Melchior FRANZ <mfranz@....at>
---

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 4462d16..8ea3543 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -568,7 +568,7 @@ static void delete_char(struct vc_data *vc, unsigned 
int nr)
  			vc->vc_cols - vc->vc_x);
  }

-static int softcursor_original;
+static int softcursor_original = -1;

  static void add_softcursor(struct vc_data *vc)
  {
--
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