[PATCH 1/2] reboot: add a "power cycle" quirk to prepare for a power off on reboot

[Simon Arlott <simon@octiron.net>]

I need to use "reboot=p" on my desktop because one of the PCIe devices
does not appear after a warm boot. This results in a very cold boot
because the BIOS turns the PSU off and on.

The scsi sd shutdown process does not send a stop command to disks
before the reboot happens (stop commands are only sent for a shutdown).

The result is that all of my SSDs experience a sudden power loss on
every reboot, which is undesirable behaviour because it could cause data
to be corrupted. These events are recorded in the SMART attributes.

Add a "power cycle" quirk to the reboot options to prepare all devices for
a power off by setting the system_state to SYSTEM_POWER_OFF instead of
SYSTEM_RESTART while still performing a restart as requested.

This uses the letter "C" for the parameter because of numerous uses of
"reboot=pci" that would otherwise trigger this behaviour if "c" was used.

Signed-off-by: Simon Arlott <simon@octiron.net>
---
Previous patches to make scsi/sd stop before a reboot:
https://lore.kernel.org/lkml/499138c8-b6d5-ef4a-2780-4f750ed337d3@0882a8b5-c6c3-11e9-b005-00805fc181fe/
https://lore.kernel.org/lkml/e726ffd8-8897-4a79-c3d6-6271eda8aebb@0882a8b5-c6c3-11e9-b005-00805fc181fe/

 Documentation/admin-guide/kernel-parameters.txt |  8 ++++++--
 include/linux/reboot.h                          |  4 ++++
 kernel/reboot.c                                 | 15 ++++++++++++++-
 3 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index bee3b83d6f84..91359fd4fbcc 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4422,9 +4422,10 @@
 	reboot=		[KNL]
 			Format (x86 or x86_64):
 				[w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
-				[[,]s[mp]#### \
+				[[,]s[mp]####] \
 				[[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
-				[[,]f[orce]
+				[[,]f[orce]] \
+				[[,]C]
 			Where reboot_mode is one of warm (soft) or cold (hard) or gpio
 					(prefix with 'panic_' to set mode for panic
 					reboot only),
@@ -4432,6 +4433,9 @@
 			      reboot_force is either force or not specified,
 			      reboot_cpu is s[mp]#### with #### being the processor
 					to be used for rebooting.
+			Quirks:
+				C = Rebooting includes a power cycle, prepare
+				    for a power off instead of a restart.
 
 	refscale.holdoff= [KNL]
 			Set test-start holdoff period.  The purpose of
diff --git a/include/linux/reboot.h b/include/linux/reboot.h
index 3734cd8f38a8..b49559ba825a 100644
--- a/include/linux/reboot.h
+++ b/include/linux/reboot.h
@@ -39,6 +39,10 @@ extern int reboot_default;
 extern int reboot_cpu;
 extern int reboot_force;
 
+#define REBOOT_QUIRK_POWER_CYCLE                BIT(0)
+
+extern int reboot_quirks;
+
 
 extern int register_reboot_notifier(struct notifier_block *);
 extern int unregister_reboot_notifier(struct notifier_block *);
diff --git a/kernel/reboot.c b/kernel/reboot.c
index 491f1347bf43..5605c2894f2b 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -45,6 +45,7 @@ int reboot_default = 1;
 int reboot_cpu;
 enum reboot_type reboot_type = BOOT_ACPI;
 int reboot_force;
+int reboot_quirks;
 
 /*
  * If set, this is used for preparing the system to power off.
@@ -71,7 +72,15 @@ EXPORT_SYMBOL_GPL(emergency_restart);
 void kernel_restart_prepare(char *cmd)
 {
 	blocking_notifier_call_chain(&reboot_notifier_list, SYS_RESTART, cmd);
-	system_state = SYSTEM_RESTART;
+	if (reboot_quirks & REBOOT_QUIRK_POWER_CYCLE) {
+		/*
+		 * The reboot will include a power cycle, so prepare all
+		 * devices for a power off.
+		 */
+		system_state = SYSTEM_POWER_OFF;
+	} else {
+		system_state = SYSTEM_RESTART;
+	}
 	usermodehelper_disable();
 	device_shutdown();
 }
@@ -583,6 +592,10 @@ static int __init reboot_setup(char *str)
 		case 'f':
 			reboot_force = 1;
 			break;
+
+		case 'C':
+			reboot_quirks |= REBOOT_QUIRK_POWER_CYCLE;
+			break;
 		}
 
 		str = strchr(str, ',');
-- 
2.17.1

-- 
Simon Arlott