Bugfix: Bad battery percentage reporting in sleepd

<2014-06-11 Wed>

I got a power outage at home last night, my laptop got suspended in a few seconds after the AC power off. It kept going to suspended every times I woke it up. I checked my battery but found that it was nearly full charged. So what's wrong?

It must be the sleepd, I thought. My parameters for sleepd was so simple:

#file /etc/default/sleepd
PARAMS="-u 0 -b 30"

By setting -u to 6000 and -b to 3 respectively, I found the problem was about the battery percentage reporting(when set -b to 3 the laptop didn't suspend).

After reading the source and doing some debug, I found this line in acpi.c:

info->battery_percentage = 100 * pcap / acpi_batt_capacity[battery];

Both pcap and acpi_batt_capacity[battery] are 32-bits integer. Their values are 55840000 and 57970000 on my laptop, and 100 * 55840000 is greater than the max 32-bits integer, so it's overflowed: The buggy result of the battery_percentage is about 23, it's below my setting (-b 30).

I changed these variables from int to int64_t, and problem solved.

Here is the patch: https://github.com/KDr2/kultivate/blob/master/patches/sleepd/0001-use-int64_t-for-battery-capacity-to-avoid-integer-ov.patch