Re: [PATCH] acpi: button: Provide option for power button to directly signal init
From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: 2020-01-30 21:07:22
Also in:
linux-acpi, lkml
On Sat, Jan 11, 2020 at 3:21 AM Josh Triplett [off-list ref] wrote:
Virtual machines and containers often use an ACPI power button event to tell the machine to shut down gracefully. Provide an optional, extremely lightweight way 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.
Well, I'm not convinced. Even though the patch looks straightforward, the approach really is quite not so conceptually and honestly it looks like a band-aid. Also I'm not quite sure why the ACPI button driver is the target of this and not the input layer, for instance.
quoted hunk ↗ jump to hunk
By default, the power button will continue to notify userspace through the input layer. With the button.power_signal parameter set, the power button will instead send the configured signal to init. (For instance, sending SIGINT will make the power button simulate ctrl-alt-del.) Signed-off-by: Josh Triplett <josh@joshtriplett.org> --- Documentation/admin-guide/kernel-parameters.txt | 6 ++++++ drivers/acpi/button.c | 11 +++++++++++ 2 files changed, 17 insertions(+)diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index ade4e6ec23e0..bbb598e148f4 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt@@ -450,6 +450,12 @@ firmware feature for flushing multiple hpte entries at a time. + button.power_signal= + [ACPI] When the power button is pressed, send this + signal number to the init process. If set to 0 + (default), do not send a signal. + Format: integer + c101= [NET] Moxa C101 synchronous serial card cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.diff --git a/drivers/acpi/button.c b/drivers/acpi/button.c index b758b45737f5..923259f132d6 100644 --- a/drivers/acpi/button.c +++ b/drivers/acpi/button.c@@ -14,6 +14,7 @@ #include <linux/init.h> #include <linux/types.h> #include <linux/proc_fs.h> +#include <linux/sched/signal.h> #include <linux/seq_file.h> #include <linux/input.h> #include <linux/slab.h>@@ -167,6 +168,10 @@ static unsigned long lid_report_interval __read_mostly = 500; module_param(lid_report_interval, ulong, 0644); MODULE_PARM_DESC(lid_report_interval, "Interval (ms) between lid key events"); +static int power_signal __read_mostly = 0; +module_param(power_signal, int, 0644); +MODULE_PARM_DESC(power_signal, "Power button sends this signal to init"); + /* -------------------------------------------------------------------------- FS Interface (/proc) -------------------------------------------------------------------------- */@@ -426,6 +431,12 @@ static void acpi_button_notify(struct acpi_device *device, u32 event) if (button->suspended) break; + if (power_signal + && button->type == ACPI_BUTTON_TYPE_POWER) { + kill_cad_pid(power_signal, 1); + break; + } + keycode = test_bit(KEY_SLEEP, input->keybit) ? KEY_SLEEP : KEY_POWER; input_report_key(input, keycode, 1); --2.25.0.rc2