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Re: Applying correct hdparm values after resuming from suspend

On Sat, Jul 12, 2008 at 09:56:35 +0300, Arthur A wrote:
> Hi list,
> I'm using Debian Lenny with Laptop-mode tools that I've configured to 
> manage my laptop's hd, which is controlled by firmware that gives insane 
> load cycle values. Thus, I've enabled laptop-mode-tools and it currently 
> applies a setting of 254 (disabled) when running on AC and 128 (enabled 
> and aggressive pm settings) when running on battery. This works fine on 
> boot, and when removing or inserting the AC power. However, upon resume a 
> setting of 128 is applied regardless of the machine's powerstate.
> I believe that laptop-mode is being restarted correctly since if I remove 
> and reinsert the AC cord the correct hdparm settings (254) are applied. 
> My guess is that something is also being re-initialized upon resume from 
> suspend that is over-riding laptop-mode-tools. In any event, I thought 
> that the simplest fix for this would be to add a script to 
> /etc/pm/sleep.d/01-hdparm-power-check which would do nothing if going to 
> sleep, and if resuming would check whether the computer was running on 
> ac, and if so apply hdparm -B 254 /dev/sda
> My problem lies in this second part, as I'm not sure how to correctly do 
> a check, the rest of it I can steal from other scripts included under  
> /usr/lib/pm-utils/sleep.d/
> This is what I think 01-hdparm-power-check would look like:


I would first check if the "on_ac_power" command works reliably on your
system. If you run

on_ac_power; echo $?

then you should get 0 (true) if you are connected to AC power and 1
(false) if you are running on battery. (See "man on_ac_power"; the "echo
$?" part is necessary to print the exit status.)

If that is OK then your script should work like this:

# Check to see if we are running on AC power, and if so,
# override mystery program overriding laptop-mode.conf


on_ac_power || exit $NA

case "$1" in
       hdparm -B 254 /dev/sda
   *) exit $NA

The double pipe "||" is the logical OR operator. If on_ac_power returns
true then the OR expression is already true overall and the shell will
therefore not even bother to evaluate the second argument; it goes
directly to the case structure. If on_ac_power returns false, on the
other hand, then the shell has to evaluate the second argument, which
makes it exit with status $NA. 

Note: I have to admit that I am not entirely sure about the role of the
$NA variable; I assume it is properly defined in the context of these
scripts since many of the other sleep.d hooks use it in the same way.

Regards,            | http://users.icfo.es/Florian.Kulzer
          Florian   |

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