[PATCH v3 0/7] TTY Keyboard Status Request

[Arseny Maslennikov <ar@cs.msu.ru>]

This patch series introduces TTY keyboard status request, a feature of
the n_tty line discipline that reserves a character in struct termios
(^T by default) and reacts to it by printing a short informational line
to the terminal and sending a Unix signal to the tty's foreground
process group. The processes may, in response to the signal, output a
textual description of what they're doing.

The feature has been present in a similar form at least in
Free/Open/NetBSD; it would be nice to have something like this in Linux
as well. There is an LKML thread[1] where users have previously
expressed the rationale for this.

The current implementation does not break existing kernel API in any
way, since, fortunately, all the architectures supported by the kernel
happen to have at least 1 free byte in the termios control character
array.

Patches 1-4 implement the semantics of the new signal and VSTATUS cc;
patches 5-7 implement the kerninfo line written to the terminal by n_tty.

The series should cleanly apply to tty-next and 5.7-rc3.

[1] https://lore.kernel.org/lkml/1415200663.3247743.187387481.75CE9317@webmail.messagingengine.com/

v2 <- v1: removed useless debugging bits.
v3 <- v2: made commit message clarifications sparked by previous
discussion, adapted 7/7 for y2038, re-Cc linux-api@.

Discussion of v1:
https://lore.kernel.org/lkml/20190605081906.28938-1-ar@cs.msu.ru/
Discussion of v2:
https://lore.kernel.org/lkml/20190625161153.29811-1-ar@cs.msu.ru/

Arseny Maslennikov (7):
  signal.h: Define SIGINFO on all architectures
  tty: termios: Reserve space for VSTATUS in .c_cc
  n_tty: Send SIGINFO to fg pgrp on status request character
  linux/signal.h: Ignore SIGINFO by default in new tasks
  tty: Add NOKERNINFO lflag to termios
  n_tty: ->ops->write: Cut core logic out to a separate function
  n_tty: Provide an informational line on VSTATUS receipt

 arch/alpha/include/asm/termios.h         |   4 +-
 arch/alpha/include/uapi/asm/termbits.h   |   2 +
 arch/arm/include/uapi/asm/signal.h       |   1 +
 arch/h8300/include/uapi/asm/signal.h     |   1 +
 arch/ia64/include/asm/termios.h          |   4 +-
 arch/ia64/include/uapi/asm/signal.h      |   1 +
 arch/ia64/include/uapi/asm/termbits.h    |   2 +
 arch/m68k/include/uapi/asm/signal.h      |   1 +
 arch/mips/include/asm/termios.h          |   4 +-
 arch/mips/include/uapi/asm/signal.h      |   1 +
 arch/mips/include/uapi/asm/termbits.h    |   2 +
 arch/parisc/include/asm/termios.h        |   4 +-
 arch/parisc/include/uapi/asm/signal.h    |   1 +
 arch/parisc/include/uapi/asm/termbits.h  |   2 +
 arch/powerpc/include/asm/termios.h       |   4 +-
 arch/powerpc/include/uapi/asm/signal.h   |   1 +
 arch/powerpc/include/uapi/asm/termbits.h |   2 +
 arch/s390/include/asm/termios.h          |   4 +-
 arch/s390/include/uapi/asm/signal.h      |   1 +
 arch/sparc/include/asm/termios.h         |   4 +-
 arch/sparc/include/uapi/asm/signal.h     |   2 +
 arch/sparc/include/uapi/asm/termbits.h   |   2 +
 arch/x86/include/uapi/asm/signal.h       |   1 +
 arch/xtensa/include/uapi/asm/signal.h    |   1 +
 arch/xtensa/include/uapi/asm/termbits.h  |   2 +
 drivers/tty/Makefile                     |   3 +-
 drivers/tty/n_tty.c                      |  70 ++++-
 drivers/tty/n_tty_status.c               | 338 +++++++++++++++++++++++
 include/asm-generic/termios.h            |   4 +-
 include/linux/sched.h                    |   7 +
 include/linux/signal.h                   |   5 +-
 include/linux/tty.h                      |   7 +-
 include/uapi/asm-generic/signal.h        |   1 +
 include/uapi/asm-generic/termbits.h      |   2 +
 34 files changed, 458 insertions(+), 33 deletions(-)
 create mode 100644 drivers/tty/n_tty_status.c

-- 
2.26.2