[Bug 1548392] Re: Fix for 1172692 fails to restore hibernation mode with suspend-hybrid

Mon Feb 22 20:56:20 UTC 2016

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On 2012-07-27T07:25:40+00:00 Jskarvad wrote:

Created attachment 64764
Add support for in-kernel suspend to both.

>From kernel-3.6 there is in-kernel support for suspend to both (AKA
hybrid suspend).

Original report with patch from Bojan (also added as attachment):
https://bugzilla.redhat.com/show_bug.cgi?id=843657

Reply at: https://bugs.launchpad.net/ubuntu/+source/pm-
utils/+bug/1548392/comments/0

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On 2012-10-17T14:39:31+00:00 Jskarvad wrote:

Created attachment 68712
Improved patch to save previous hibernation method

https://bugzilla.redhat.com/show_bug.cgi?id=866487

Reply at: https://bugs.launchpad.net/ubuntu/+source/pm-
utils/+bug/1548392/comments/1

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On 2016-02-07T15:29:53+00:00 Dirk F wrote:

Comment on attachment 68712
Improved patch to save previous hibernation method

Review of attachment 68712:
-----------------------------------------------------------------

In do_hibernate() the attempt to save and restore the active mode in
/sys/power/disk fails, causing "sh: I/O error" message in pm log
(attempting to write something that isn't one of the modes in
/sys/power/disk, namely an empty string). Instrumenting the function I
found that HIBERNATE_MODE_SAVE was never set.

The characters [] are special in a shell pattern (which is what follows
the ## and %% shell variable expansion modifiers) and have to be
escaped: \[ \].

The following works as you intended:

do_hibernate()
	{
		[ -n "${HIBERNATE_MODE}" ] && \
		grep -qw "${HIBERNATE_MODE}" /sys/power/disk && \
		#df 2016-02-07 Shell patterns have to be escaped \[ \]! Fixes sh: I/O error when -z $HIBERNATE_MODE_SAVE 
		HIBERNATE_MODE_SAVE=$(cat /sys/power/disk) && \
		HIBERNATE_MODE_SAVE="${HIBERNATE_MODE_SAVE##*\[}" && \
		HIBERNATE_MODE_SAVE="${HIBERNATE_MODE_SAVE%%\]*}" && \
		echo -n "${HIBERNATE_MODE}" > /sys/power/disk
		echo -n "disk" > /sys/power/state
		RET=$?
		echo -n "$HIBERNATE_MODE_SAVE" > /sys/power/disk
		return "$RET"
	}

Although you could make the penultimate line as follows I don't
recommend it because it would hide any problems like the escaping issue
that could cause HIBERNATE_MODE_SAVE to be invalid:

                [ -n "$HIBERNATE_MODE_SAVE" ] && echo -n
"$HIBERNATE_MODE_SAVE" > /sys/power/disk

Reply at: https://bugs.launchpad.net/ubuntu/+source/pm-
utils/+bug/1548392/comments/2

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On 2016-02-22T16:38:16+00:00 Dirk F wrote:

In comment #2 I wrote:
> Comment on attachment 68712 [details] [review]
>...
> Although you could make the penultimate line as follows I don't recommend it
> because it would hide any problems like the escaping issue that could cause
> HIBERNATE_MODE_SAVE to be invalid:
> 
> 		[ -n "$HIBERNATE_MODE_SAVE" ] && echo -n "$HIBERNATE_MODE_SAVE" >
> /sys/power/disk

In fact there are 2 cases as the code is used now:

1    HIBERNATE_MODE unset => normal hibernate

2    HIBERNATE_MODE = suspend => suspend-hybrid

Given which, I've revised my comment above and propose a new version of
the modified do_hibernate() as follows:

	do_hibernate()
	{
		local hibernate_mode_save ret

		[ -n "${HIBERNATE_MODE}" ] && \
		 grep -qw "${HIBERNATE_MODE}" /sys/power/disk && \
		 hibernate_mode_save=$(cat /sys/power/disk) && \
		 hibernate_mode_save="${hibernate_mode_save##*\[}" && \
		 hibernate_mode_save="${hibernate_mode_save%%\]*}" && \
		 [ "$hibernate_mode_save" != "${HIBERNATE_MODE}" ]  || \
		 hibernate_mode_save=""
		[ -n "$hibernate_mode_save" ] && \
		 echo -n "${HIBERNATE_MODE}" > /sys/power/disk
		echo -n "disk" > /sys/power/state
		ret=$?
		[ -n "$hibernate_mode_save" ] && \
		 echo -n "$hibernate_mode_save" > /sys/power/disk
		return $ret
	}

The key points:
- hibernate_mode_save is only set if the current HIBERNATE_MODE is being changed (which only happens, if it does, in the suspend-hybrid case);
- on resume the hibernate mode is only restored if hibernate_mode_save was set.

This fixes:
- the failure to restore the hibernate mode with suspend-hybrid;
- "sh: I/O error" on resume from suspend-hybrid
- "sh: I/O error" on resume from hibernate.

Finally, the pm_functions script uses "echo -n" (from line 318,
including the above patch) and local declarations while the comment
against function log() implies that the script is aiming for POSIX
conformance and yet other functions use non-POSIX local declarations.
local and "echo -n" usages are fine for Debian and derived environments.
To achieve POSIX conformance such usages would have to be reviewed and
modified; "echo -n" could be replaced with printf (the parameters to be
echoed in each case being plain text not containing formatting
commands); or a shell function echo() can be added based on log().

Reply at: https://bugs.launchpad.net/ubuntu/+source/pm-
utils/+bug/1548392/comments/3

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On 2016-02-22T20:38:39+00:00 Dirk F wrote:

In comment #3 I wrote:
>...
> Finally, the pm_functions script uses "echo -n" (from line 318, including
> the above patch) ...