This is a note to let you know that I've just added the patch titled

tty: vt.c: Fix TIOCL_BLANKSCREEN console blanking if blankinterval ==

to my tty git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git in the tty-next branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release during the merge window.

If you have any questions about this process, please let me know.

From 75ddbc1fb11efac87b611d48e9802f6fe2bb2163 Mon Sep 17 00:00:00 2001

From: Yifeng Li tomli@tomli.me Date: Tue, 5 Mar 2019 07:02:49 +0800 Subject: tty: vt.c: Fix TIOCL_BLANKSCREEN console blanking if blankinterval == 0

Previously, in the userspace, it was possible to use the "setterm" command from util-linux to blank the VT console by default, using the following command.

According to the man page,

The force option keeps the screen blank even if a key is pressed.

It was implemented by calling TIOCL_BLANKSCREEN.

case BLANKSCREEN: ioctlarg = TIOCL_BLANKSCREEN; if (ioctl(STDIN_FILENO, TIOCLINUX, &ioctlarg)) warn(_("cannot force blank")); break;

However, after Linux 4.12, this command ceased to work anymore, which is unexpected. By inspecting the kernel source, it shows that the issue was triggered by the side-effect from commit a4199f5eb809 ("tty: Disable default console blanking interval").

The console blanking is implemented by function do_blank_screen() in vt.c: "blank_state" will be initialized to "blank_normal_wait" in con_init() if AND ONLY IF ("blankinterval" > 0). If "blankinterval" is 0, "blank_state" will be "blank_off" (== 0), and a call to do_blank_screen() will always abort, even if a forced blanking is required from the user by calling TIOCL_BLANKSCREEN, the console won't be blanked.

This behavior is unexpected from a user's point-of-view, since it's not mentioned in any documentation. The setterm man page suggests it will always work, and the kernel comments in uapi/linux/tiocl.h says

/* keep screen blank even if a key is pressed */ #define TIOCL_BLANKSCREEN 14

To fix it, we simply remove the "blank_state != blank_off" check, as pointed out by Nicolas Pitre, this check doesn't logically make sense and it's safe to remove.

Suggested-by: Nicolas Pitre nicolas.pitre@linaro.org Fixes: a4199f5eb809 ("tty: Disable default console blanking interval") Signed-off-by: Yifeng Li tomli@tomli.me Cc: stable stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/vt/vt.c | 2 -- 1 file changed, 2 deletions(-)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c index d34984aa646d..721edee50234 100644 --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -4178,8 +4178,6 @@ void do_blank_screen(int entering_gfx) return; }

- if (blank_state != blank_normal_wait) - return; blank_state = blank_off;

/* don't blank graphics */