Commit a1b93e89 authored by Josh Triplett's avatar Josh Triplett Committed by Rafael J. Wysocki
Browse files

ACPI: Add new tiny-power-button driver to directly signal init 



Virtual machines often use an ACPI power button event to tell the
machine to shut down gracefully.

Provide an extremely lightweight "tiny power button" driver to handle
this event by signaling init directly, rather than running a separate
daemon (such as acpid or systemd-logind) that adds to startup time and
VM image complexity.

The kernel configuration defines the default signal to send init, and
userspace can change this signal via a module parameter.

Suggested-by: default avatar"Rafael J. Wysocki" <rafael@kernel.org>
Signed-off-by: default avatarJosh Triplett <josh@joshtriplett.org>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent ac1cc6b4

drivers/acpi/Kconfig

+24 −0
Original line number Diff line number Diff line
@@ -190,6 +190,30 @@ config ACPI_BUTTON 
	  To compile this driver as a module, choose M here:

	  the module will be called button.



config ACPI_TINY_POWER_BUTTON

	tristate "Tiny Power Button Driver"

	depends on !ACPI_BUTTON

	help

	  This driver provides a tiny alternative to the ACPI Button driver.

	  The tiny power button driver only handles the power button. Rather

	  than notifying userspace via the input layer or a netlink event, this

	  driver directly signals the init process to shut down.



	  This driver is particularly suitable for cloud and VM environments,

	  which use a simulated power button to initiate a controlled poweroff,

	  but which may not want to run a separate userspace daemon to process

	  input events.



config ACPI_TINY_POWER_BUTTON_SIGNAL

	int "Tiny Power Button Signal"

	depends on ACPI_TINY_POWER_BUTTON

	default 38

	help

	  Default signal to send to init in response to the power button.



	  Likely values here include 38 (SIGRTMIN+4) to power off, or 2

	  (SIGINT) to simulate Ctrl+Alt+Del.



config ACPI_VIDEO

	tristate "Video"

	depends on X86 && BACKLIGHT_CLASS_DEVICE

drivers/acpi/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -71,6 +71,7 @@ obj-$(CONFIG_ACPI_IPMI) += acpi_ipmi.o 


obj-$(CONFIG_ACPI_AC) 		+= ac.o

obj-$(CONFIG_ACPI_BUTTON)	+= button.o

obj-$(CONFIG_ACPI_TINY_POWER_BUTTON)	+= tiny-power-button.o

obj-$(CONFIG_ACPI_FAN)		+= fan.o

obj-$(CONFIG_ACPI_VIDEO)	+= video.o

obj-$(CONFIG_ACPI_TAD)		+= acpi_tad.o

drivers/acpi/tiny-power-button.c

0 → 100644
+46 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0-or-later

#include <linux/module.h>

#include <linux/sched/signal.h>

#include <linux/acpi.h>

#include <acpi/button.h>



ACPI_MODULE_NAME("tiny-power-button");

MODULE_AUTHOR("Josh Triplett");

MODULE_DESCRIPTION("ACPI Tiny Power Button Driver");

MODULE_LICENSE("GPL");



static int power_signal __read_mostly = CONFIG_ACPI_TINY_POWER_BUTTON_SIGNAL;

module_param(power_signal, int, 0644);

MODULE_PARM_DESC(power_signal, "Power button sends this signal to init");



static const struct acpi_device_id tiny_power_button_device_ids[] = {

	{ ACPI_BUTTON_HID_POWER, 0 },

	{ ACPI_BUTTON_HID_POWERF, 0 },

	{ "", 0 },

};

MODULE_DEVICE_TABLE(acpi, tiny_power_button_device_ids);



static int acpi_noop_add_remove(struct acpi_device *device)

{

	return 0;

}



static void acpi_tiny_power_button_notify(struct acpi_device *device, u32 event)

{

	kill_cad_pid(power_signal, 1);

}



static struct acpi_driver acpi_tiny_power_button_driver = {

	.name = "tiny-power-button",

	.class = "tiny-power-button",

	.ids = tiny_power_button_device_ids,

	.ops = {

		.add = acpi_noop_add_remove,

		.remove = acpi_noop_add_remove,

		.notify = acpi_tiny_power_button_notify,

	},

};



module_driver(acpi_tiny_power_button_driver,

		acpi_bus_register_driver,

		acpi_bus_unregister_driver);

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