This is a note to let you know that I've just added the patch titled
vt: change SGR 21 to follow the standards
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 65d9982d7e523a1a8e7c9af012da0d166f72fc56 Mon Sep 17 00:00:00 2001
From: Mike Frysinger vapier@chromium.org Date: Mon, 29 Jan 2018 17:08:21 -0500 Subject: vt: change SGR 21 to follow the standards
ECMA-48 [1] (aka ISO 6429) has defined SGR 21 as "doubly underlined" since at least March 1984. The Linux kernel has treated it as SGR 22 "normal intensity" since it was added in Linux-0.96b in June 1992. Before that, it was simply ignored. Other terminal emulators have either ignored it, or treat it as double underline now. xterm for example added support in its 304 release (May 2014) [2] where it was previously ignoring it.
Changing this behavior shouldn't be an issue: - It isn't a named capability in ncurses's terminfo database, so no script is using libtinfo/libcurses to look this up, or using tput to query & output the right sequence. - Any script assuming SGR 21 will reset intensity in all terminals already do not work correctly on non-Linux VTs (including running under screen/tmux/etc...). - If someone has written a script that only runs in the Linux VT, and they're using SGR 21 (instead of SGR 22), the output should still be readable.
imo it's important to change this as the Linux VT's non-conformance is sometimes used as an argument for other terminal emulators to not implement SGR 21 at all, or do so incorrectly.
[1]: https://www.ecma-international.org/publications/standards/Ecma-048.htm [2]: https://github.com/ThomasDickey/xterm-snapshots/commit/2fd29cb98d214cb536bca...
Signed-off-by: Mike Frysinger vapier@chromium.org Cc: stable stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/vt/vt.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c index 88b902c525d7..16c0fcd6904a 100644 --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -1354,6 +1354,11 @@ static void csi_m(struct vc_data *vc) case 3: vc->vc_italic = 1; break; + case 21: + /* + * No console drivers support double underline, so + * convert it to a single underline. + */ case 4: vc->vc_underline = 1; break; @@ -1389,7 +1394,6 @@ static void csi_m(struct vc_data *vc) vc->vc_disp_ctrl = 1; vc->vc_toggle_meta = 1; break; - case 21: case 22: vc->vc_intensity = 1; break;