ubifs robustness with early power cut warning

ubifs robustness with early power cut warning

[Doug Crawford]

We have an embedded system with an early power loss warning.  The
power supply drives a powerdown signal connected to a GPIO pin on the
CPU.  When AC power is switched off the power supply drives this
signal low for 500 milliseconds before the CPU gets held in reset.  If
AC power is switched back on before 500 milliseconds the powerdown
signal goes high again and the system is expected to continue running
normally.

I am wondering if there is a way to easily modify ubifs/ubi such that
when the powerdown gpio is low VFS or UBIFS or UBI freezes or pauses
further writes to the NAND.  If powerdown recovers to high again then
the filesystem would unfreeze and allow further writes?  Has anyone
implemented something like this before?  I know UBIFS/UBI is designed
to be very resilient to power cuts, but I am thinking this technique
might make the system even more resilient.  If I were to make this
change which file would be the right one to hook into:
fs/ubifs/super.c?

Re: ubifs robustness with early power cut warning

[Richard Weinberger]

On Sat, Sep 30, 2017 at 1:20 AM, Doug Crawford <dcraw101@gmail.com> wrote:
> We have an embedded system with an early power loss warning.  The
> power supply drives a powerdown signal connected to a GPIO pin on the
> CPU.  When AC power is switched off the power supply drives this
> signal low for 500 milliseconds before the CPU gets held in reset.  If
> AC power is switched back on before 500 milliseconds the powerdown
> signal goes high again and the system is expected to continue running
> normally.
>
> I am wondering if there is a way to easily modify ubifs/ubi such that
> when the powerdown gpio is low VFS or UBIFS or UBI freezes or pauses
> further writes to the NAND.  If powerdown recovers to high again then
> the filesystem would unfreeze and allow further writes?  Has anyone
> implemented something like this before?  I know UBIFS/UBI is designed
> to be very resilient to power cuts, but I am thinking this technique
> might make the system even more resilient.  If I were to make this
> change which file would be the right one to hook into:
> fs/ubifs/super.c?

UBI/UBIFS is the wrong layer, this needs to happen in MTD.

-- 
Thanks,
//richard

Re: ubifs robustness with early power cut warning

[Doug Crawford]

I think my use case might be a little different. This 500 millisecond
early power down warning is intended to be recoverable if the power is
restored in that period.  The effect I am looking for is that any new
fsync or sync commands made during this 500 ms window will pause or
block, but if the power is restored then the sync will be successful.

I am worried that if mtd_write() returns an EPERM error then any
outstanding fsync or syncs would fail instead of block?  I don't know
enough about the mtd layer or the locking/calling context of
mtd_write().  But, I am guessing I can't simply sleep or block in that
function while the powerdown gpio is low?

On Sat, Sep 30, 2017 at 9:19 AM, Richard Weinberger
<richard.weinberger@gmail.com> wrote:
> On Sat, Sep 30, 2017 at 1:20 AM, Doug Crawford <dcraw101@gmail.com> wrote:
>> We have an embedded system with an early power loss warning.  The
>> power supply drives a powerdown signal connected to a GPIO pin on the
>> CPU.  When AC power is switched off the power supply drives this
>> signal low for 500 milliseconds before the CPU gets held in reset.  If
>> AC power is switched back on before 500 milliseconds the powerdown
>> signal goes high again and the system is expected to continue running
>> normally.
>>
>> I am wondering if there is a way to easily modify ubifs/ubi such that
>> when the powerdown gpio is low VFS or UBIFS or UBI freezes or pauses
>> further writes to the NAND.  If powerdown recovers to high again then
>> the filesystem would unfreeze and allow further writes?  Has anyone
>> implemented something like this before?  I know UBIFS/UBI is designed
>> to be very resilient to power cuts, but I am thinking this technique
>> might make the system even more resilient.  If I were to make this
>> change which file would be the right one to hook into:
>> fs/ubifs/super.c?
>
> UBI/UBIFS is the wrong layer, this needs to happen in MTD.
>
> --
> Thanks,
> //richard

Re: ubifs robustness with early power cut warning

[Richard Weinberger]

Am Montag, 2. Oktober 2017, 18:14:28 CEST schrieb Doug Crawford:
> I think my use case might be a little different. This 500 millisecond
> early power down warning is intended to be recoverable if the power is
> restored in that period.  The effect I am looking for is that any new
> fsync or sync commands made during this 500 ms window will pause or
> block, but if the power is restored then the sync will be successful.

Hmm, if I understand your correctly, all you need is freeze/thaw support in 
UBIFS.
Upon power-loss you freeze the filesystem and if power recovers you can thaw 
it.

Does this information help? :-)

Thanks,
//richard

-- 
sigma star gmbh - Eduard-Bodem-Gasse 6 - 6020 Innsbruck - Austria
ATU66964118 - FN 374287y

Re: ubifs robustness with early power cut warning

[Doug Crawford]

the freeze/thaw sounds like what I need.  I guess using the fsfreeze
tool from util-linux would work?  Is all of that implemented in the
VFS layer?  I see some recent patches for adding UBIFS specific
freeze/thaw functionality?

On Mon, Oct 2, 2017 at 9:45 AM, Richard Weinberger
<richard@sigma-star.at> wrote:
> Am Montag, 2. Oktober 2017, 18:14:28 CEST schrieb Doug Crawford:
>> I think my use case might be a little different. This 500 millisecond
>> early power down warning is intended to be recoverable if the power is
>> restored in that period.  The effect I am looking for is that any new
>> fsync or sync commands made during this 500 ms window will pause or
>> block, but if the power is restored then the sync will be successful.
>
> Hmm, if I understand your correctly, all you need is freeze/thaw support in
> UBIFS.
> Upon power-loss you freeze the filesystem and if power recovers you can thaw
> it.
>
> Does this information help? :-)
>
> Thanks,
> //richard
>
> --
> sigma star gmbh - Eduard-Bodem-Gasse 6 - 6020 Innsbruck - Austria
> ATU66964118 - FN 374287y

Re: ubifs robustness with early power cut warning

[Richard Weinberger]

Am Montag, 2. Oktober 2017, 19:33:01 CEST schrieb Doug Crawford:
> the freeze/thaw sounds like what I need.  I guess using the fsfreeze
> tool from util-linux would work?  Is all of that implemented in the
> VFS layer?  I see some recent patches for adding UBIFS specific
> freeze/thaw functionality?

Currently UBIFS does not support freeze/thaw.
But adding this feature shouldn't be a big deal.

On the other hand, if your application behaves correctly power-cut would
never cause data loss.
If you do, UBIFS or the MTD driver are buggy.

Thanks,
//richard

-- 
sigma star gmbh - Eduard-Bodem-Gasse 6 - 6020 Innsbruck - Austria
ATU66964118 - FN 374287y

Re: ubifs robustness with early power cut warning

[Kees Trommel]

[-- Attachment #1: Type: text/plain, Size: 1583 bytes --]

Doug,

Attached a patch file with an implementation that I developed for our 
custom board that has an early powerdown (is dying) signal (GPIO pin).

The idea is that when an "I am dying" condition is detected no erase or 
program is started by the mtd layer. It is assumed that an erase or 
program started before the board starts to die will be completed 
successfully.

Kees.

On 09/30/17 01:20, Doug Crawford wrote:
> We have an embedded system with an early power loss warning.  The
> power supply drives a powerdown signal connected to a GPIO pin on the
> CPU.  When AC power is switched off the power supply drives this
> signal low for 500 milliseconds before the CPU gets held in reset.  If
> AC power is switched back on before 500 milliseconds the powerdown
> signal goes high again and the system is expected to continue running
> normally.
>
> I am wondering if there is a way to easily modify ubifs/ubi such that
> when the powerdown gpio is low VFS or UBIFS or UBI freezes or pauses
> further writes to the NAND.  If powerdown recovers to high again then
> the filesystem would unfreeze and allow further writes?  Has anyone
> implemented something like this before?  I know UBIFS/UBI is designed
> to be very resilient to power cuts, but I am thinking this technique
> might make the system even more resilient.  If I were to make this
> change which file would be the right one to hook into:
> fs/ubifs/super.c?
>
> ______________________________________________________
> Linux MTD discussion mailing list
> http://lists.infradead.org/mailman/listinfo/linux-mtd/



[-- Attachment #2: mtd_dying.patch --]
[-- Type: text/x-patch, Size: 6999 bytes --]

diff -urN mtd_dying.org/arch/arm/configs/ls1021a_defconfig mtd_dying.new/arch/arm/configs/ls1021a_defconfig
--- mtd_dying.org/arch/arm/configs/ls1021a_defconfig	2017-10-02 09:49:04.866784219 +0200
+++ mtd_dying.new/arch/arm/configs/ls1021a_defconfig	2017-10-02 09:40:59.346787515 +0200
@@ -26,6 +26,7 @@
 CONFIG_ARCH_VIRT=y
 CONFIG_ARCH_MXC=y
 CONFIG_SOC_LS1021A=y
+CONFIG_BOARD_PSD=y
 CONFIG_ARM_LPAE=y
 # CONFIG_CACHE_L2X0 is not set
 CONFIG_PCI=y
diff -urN mtd_dying.org/arch/arm/mach-imx/Kconfig mtd_dying.new/arch/arm/mach-imx/Kconfig
--- mtd_dying.org/arch/arm/mach-imx/Kconfig	2017-10-02 09:39:36.812537914 +0200
+++ mtd_dying.new/arch/arm/mach-imx/Kconfig	2017-10-02 09:40:59.360156438 +0200
@@ -626,6 +626,14 @@
 	help
 	  This enables support for Freescale LS1021A processor.
 
+config BOARD_PSD
+	bool "AimValley PSD support"
+	depends on SOC_LS1021A
+	select CONSOLE_POLL
+
+	help
+	  This enables support for the AimValley PSD board.
+
 endif
 
 source "arch/arm/mach-imx/devices/Kconfig"
diff -urN mtd_dying.org/arch/arm/mach-imx/Makefile mtd_dying.new/arch/arm/mach-imx/Makefile
--- mtd_dying.org/arch/arm/mach-imx/Makefile	2017-10-02 09:39:36.827457495 +0200
+++ mtd_dying.new/arch/arm/mach-imx/Makefile	2017-10-02 09:40:59.374071091 +0200
@@ -109,4 +109,6 @@
 
 obj-$(CONFIG_SOC_LS1021A) += mach-ls1021a.o
 
+obj-$(CONFIG_BOARD_PSD) += board-psd.o
+
 obj-y += devices/
diff -urN mtd_dying.org/arch/arm/mach-imx/board-psd.c mtd_dying.new/arch/arm/mach-imx/board-psd.c
--- mtd_dying.org/arch/arm/mach-imx/board-psd.c	1970-01-01 01:00:00.000000000 +0100
+++ mtd_dying.new/arch/arm/mach-imx/board-psd.c	2017-10-02 09:43:40.170792532 +0200
@@ -0,0 +1,87 @@
+/*
+ * PSD specific kernel customizations
+ *
+ * Copyright (c) 2016 AimValley B.V., the Netherlands
+ * You may only use or distribute this file if you have a valid license agreement with AimValley B.V.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+ * MA 02110-1301, USA.
+ */
+
+#include "linux/printk.h"
+#include <linux/kmsg_dump.h>
+#include "linux/reboot.h"
+#include "linux/gpio.h"
+#include "linux/mtd/mtd.h"
+#include "linux/interrupt.h"
+#include "linux/tty_driver.h"
+
+#define DYING_GASP_GPIO     447
+#define CPU_SELF_RESET_GPIO 391
+
+struct tty_driver *tty = NULL;
+int tty_line = 0;
+
+static void psd_power_off_handler(void)
+{
+	pr_emerg("Cold restart\n");
+	kmsg_dump(KMSG_DUMP_POWEROFF);
+	gpio_set_value(CPU_SELF_RESET_GPIO, 1);
+}
+
+static int psd_is_dying(void)
+{
+	return gpio_get_value(DYING_GASP_GPIO);
+}
+
+static irqreturn_t psd_is_dying_irq(int irq, void* data)
+{
+	u8* s;
+
+	(void) data;
+	(void) irq;
+
+        s = "I am dying ....";
+
+	while (*s) {
+		tty->ops->poll_put_char(tty, tty_line, *s);
+		s++;
+	}
+
+	return IRQ_HANDLED;
+}
+
+static int __init psd_board_init(void)
+{
+	gpio_request(CPU_SELF_RESET_GPIO, "reset");
+	gpio_direction_output(CPU_SELF_RESET_GPIO, 0);
+	gpio_export(CPU_SELF_RESET_GPIO, false);
+
+	kernel_power_off_handler(psd_power_off_handler);
+
+	gpio_request(DYING_GASP_GPIO, "dying gasp");
+	gpio_direction_input(DYING_GASP_GPIO);
+	gpio_export(DYING_GASP_GPIO, false);
+
+	mtd_register_is_dying(psd_is_dying);
+
+	tty = tty_find_polling_driver("ttyS0", &tty_line);
+
+	return request_irq(gpio_to_irq(DYING_GASP_GPIO),
+                           psd_is_dying_irq,
+                           IRQF_TRIGGER_FALLING | IRQF_TRIGGER_RISING | IRQF_ONESHOT,
+                           "dying gasp",
+                           NULL);
+}
+late_initcall(psd_board_init);
diff -urN mtd_dying.org/drivers/mtd/mtdcore.c mtd_dying.new/drivers/mtd/mtdcore.c
--- mtd_dying.org/drivers/mtd/mtdcore.c	2017-10-02 09:39:36.738676605 +0200
+++ mtd_dying.new/drivers/mtd/mtdcore.c	2017-10-02 09:40:59.286219059 +0200
@@ -73,6 +73,7 @@
 
 static LIST_HEAD(mtd_notifiers);
 
+static int (*mtd_is_dying)(void) = NULL;
 
 #define MTD_DEVT(index) MKDEV(MTD_CHAR_MAJOR, (index)*2)
 
@@ -806,6 +807,8 @@
 		return -EINVAL;
 	if (!(mtd->flags & MTD_WRITEABLE))
 		return -EROFS;
+	if (mtd_is_dying && mtd_is_dying())
+		return -EPERM;
 	instr->fail_addr = MTD_FAIL_ADDR_UNKNOWN;
 	if (!instr->len) {
 		instr->state = MTD_ERASE_DONE;
@@ -897,6 +900,8 @@
 		return -EINVAL;
 	if (!mtd->_write || !(mtd->flags & MTD_WRITEABLE))
 		return -EROFS;
+	if (mtd_is_dying && mtd_is_dying())
+		return -EPERM;
 	if (!len)
 		return 0;
 	return mtd->_write(mtd, to, len, retlen, buf);
@@ -1204,6 +1209,27 @@
 }
 EXPORT_SYMBOL_GPL(mtd_kmalloc_up_to);
 
+/**
+ * mtd_register_is_dying - register an "is dying" callback function
+ * @is_dying: pointer to a function that returns whether the board 
+ *            "is dying" or not
+ *
+ * This routine registers an "is dying" callback function. The callback 
+ * function returns 1 if the board is dying. The board is supposed to be dying 
+ * if the board supply voltage drops below a certain voltage and soon (in few 
+ * milli seconds) will be completely powered down. This function is called in
+ * each mtd_write and mtd_erase and if the board is dying the write or erase
+ * will fail.
+ *
+ * Note: It assumes that a write or erase started before the board starts dying
+ *       can be finished before the CPU and NAND device runs out of power.
+ */
+void mtd_register_is_dying(int (*is_dying)(void))
+{
+    mtd_is_dying = is_dying;
+}
+EXPORT_SYMBOL_GPL(mtd_register_is_dying);
+
 #ifdef CONFIG_PROC_FS
 
 /*====================================================================*/
diff -urN mtd_dying.org/include/linux/mtd/mtd.h mtd_dying.new/include/linux/mtd/mtd.h
--- mtd_dying.org/include/linux/mtd/mtd.h	2017-10-02 09:39:36.766934179 +0200
+++ mtd_dying.new/include/linux/mtd/mtd.h	2017-10-02 09:40:59.314882784 +0200
@@ -422,4 +422,6 @@
 
 unsigned mtd_mmap_capabilities(struct mtd_info *mtd);
 
+void mtd_register_is_dying(int (*is_dying)(void));
+
 #endif /* __MTD_MTD_H__ */
diff -urN mtd_dying.org/include/linux/reboot.h mtd_dying.new/include/linux/reboot.h
--- mtd_dying.org/include/linux/reboot.h	2017-10-02 09:39:36.757224289 +0200
+++ mtd_dying.new/include/linux/reboot.h	2017-10-02 09:40:59.298836982 +0200
@@ -63,6 +63,7 @@
 extern void kernel_restart(char *cmd);
 extern void kernel_halt(void);
 extern void kernel_power_off(void);
+extern void kernel_power_off_handler(void (*power_off)(void));
 
 extern int C_A_D; /* for sysctl */
 void ctrl_alt_del(void);

Re: ubifs robustness with early power cut warning

[Richard Weinberger]

Kees,

On Mon, Oct 2, 2017 at 10:06 AM, Kees Trommel <ctrommel@aimvalley.nl> wrote:
> Doug,
>
> Attached a patch file with an implementation that I developed for our custom
> board that has an early powerdown (is dying) signal (GPIO pin).
>
> The idea is that when an "I am dying" condition is detected no erase or
> program is started by the mtd layer. It is assumed that an erase or program
> started before the board starts to die will be completed successfully.

Out of curiosity, did you also try to freeze or schedule the calling task?

Maybe we should add something like that to MTD as generic interface.
I saw such hacks in all variants in vendor/customer kernels.

-- 
Thanks,
//richard

Re: ubifs robustness with early power cut warning

[Kees Trommel]

Richard,

 > Out of curiosity, did you also try to freeze or schedule the calling 
task?

No I did not. When the GPIO gets active the board will die (power off) 
soon, so no need to freeze/block the calling task because it soon will 
die too.

Kees.

On 10/02/17 13:35, Richard Weinberger wrote:
> Kees,
>
> On Mon, Oct 2, 2017 at 10:06 AM, Kees Trommel <ctrommel@aimvalley.nl> wrote:
>> Doug,
>>
>> Attached a patch file with an implementation that I developed for our custom
>> board that has an early powerdown (is dying) signal (GPIO pin).
>>
>> The idea is that when an "I am dying" condition is detected no erase or
>> program is started by the mtd layer. It is assumed that an erase or program
>> started before the board starts to die will be completed successfully.
> Out of curiosity, did you also try to freeze or schedule the calling task?
>
> Maybe we should add something like that to MTD as generic interface.
> I saw such hacks in all variants in vendor/customer kernels.
>

Re: ubifs robustness with early power cut warning

[Richard Weinberger]

Am Dienstag, 3. Oktober 2017, 08:53:13 CEST schrieb Kees Trommel:
> Richard,
> 
> > Out of curiosity, did you also try to freeze or schedule the calling task?
> 
> No I did not. When the GPIO gets active the board will die (power off) so no
> need to freeze/block the calling task because it soon will die too. 

I just wondered whether the calling task does not do something stupid after 
being flooded with -EPERM upon every filesystem access.
Think of a larger software stack that communicates over a bus with other 
systems.

Thanks,
//richard

-- 
sigma star gmbh - Eduard-Bodem-Gasse 6 - 6020 Innsbruck - Austria
ATU66964118 - FN 374287y