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Yifeng Li d90824ecb8 tty: vt.c: Fix TIOCL_BLANKSCREEN console blanking if blankinterval == 0 
commit 75ddbc1fb1 upstream.

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 a4199f5eb8 ("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: a4199f5eb8 ("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>
2019-05-22 07:37:41 +02:00
arch bpf, arm64: remove prefetch insn in xadd mapping 2019-05-22 07:37:38 +02:00
block bfq: update internal depth state when queue depth changes 2019-05-16 19:41:17 +02:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto crypto: gcm - fix incompatibility between "gcm" and "gcm_base" 2019-05-22 07:37:37 +02:00
Documentation x86/speculation/mds: Improve CPU buffer clear documentation 2019-05-22 07:37:35 +02:00
drivers tty: vt.c: Fix TIOCL_BLANKSCREEN console blanking if blankinterval == 0 2019-05-22 07:37:41 +02:00
firmware
fs ocfs2: fix ocfs2 read inode data panic in ocfs2_iget 2019-05-22 07:37:40 +02:00
include mfd: max77620: Fix swapped FPS_PERIOD_MAX_US values 2019-05-22 07:37:41 +02:00
init init: initialize jump labels before command line option parsing 2019-05-16 19:41:23 +02:00
ipc ipc/shm.c: use ERR_CAST() for shm_lock() error return 2018-10-05 16:32:04 -07:00
kernel userfaultfd: use RCU to free the task struct when fork fails 2019-05-22 07:37:41 +02:00
lib ubsan: Fix nasty -Wbuiltin-declaration-mismatch GCC-9 warnings 2019-05-10 17:54:04 +02:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm hugetlb: use same fault hash key for shared and private mappings 2019-05-22 07:37:40 +02:00
net tipc: fix hanging clients using poll with EPOLLOUT flag 2019-05-16 19:41:31 +02:00
samples samples: mei: use /dev/mei0 instead of /dev/mei 2019-02-15 08:10:11 +01:00
scripts fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock 2019-05-08 07:21:51 +02:00
security selinux: do not report error on connect(AF_UNSPEC) 2019-05-16 19:41:30 +02:00
sound ASoC: codec: hdac_hdmi add device_link to card device 2019-05-22 07:37:38 +02:00
tools objtool: Fix function fallthrough detection 2019-05-22 07:37:35 +02:00
usr initramfs: move gen_initramfs_list.sh from scripts/ to usr/ 2018-08-22 23:21:44 +09:00
virt KVM: fix spectrev1 gadgets 2019-05-16 19:41:22 +02:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild
Kconfig
MAINTAINERS platform/x86: Add Intel AtomISP2 dummy / power-management driver 2019-04-20 09:16:02 +02:00
Makefile Linux 4.19.44 2019-05-16 19:41:32 +02:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.