Comment 17 for bug 1172692

Comment on attachment 68712
Improved patch to save previous hibernation method

Review of attachment 68712:
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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