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Subject[PATCH 0/7] TTY Keyboard Status Request
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.

The series should cleanly apply to tty-next.

To thoroughly test these, one might need at least a patched stty among
other tools, so I've brought up a simple initrd generator[2] which can
be used to create a lightweight environment to boot up in a VM and to
fiddle with.

[1] https://lore.kernel.org/lkml/1415200663.3247743.187387481.75CE9317@webmail.messagingengine.com/
[2] https://github.com/porrided/tty-kb-status-userspace

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 | 69 ++++-
drivers/tty/n_tty_status.c | 363 +++++++++++++++++++++++
include/asm-generic/termios.h | 4 +-
include/linux/signal.h | 5 +-
include/linux/tty.h | 7 +-
include/uapi/asm-generic/signal.h | 1 +
include/uapi/asm-generic/termbits.h | 2 +
33 files changed, 475 insertions(+), 33 deletions(-)
create mode 100644 drivers/tty/n_tty_status.c

--
2.20.1

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