The lowest layer : pm-utils

As promised, here's the first of five posts about how all the power management will fit together.

Today I'll discuss the lowest layer, pm-utils.

Sometimes we may need to unload modules or sync hardware times on suspend or resume or do certain things to certain hardware (for instance turning on the suspend LED on IBM hardware) and also do vendor specific things. The problem domain seems vast, but the problems are all small and simple if broken down.

There are numerous different admin scripts and side-programs invented by modern distros (such as Redhat pm-utils, Ubuntu acpi-support and SuSe Powersave) but there has not been any standardization between distros or vendors.

This is where pm-utils steps in.

The idea of pm-utils is for really simple scripts to be installed, and then for software and hardware vendors to just install a simple script in a standard location to do something insane.

For instance, vmware could install the vmware suspend script (to suspend a vmware session before we hibernate) into a standard place without having to bodge each distro setup individually. In this way, the smallest distros get the same level of compatibility and integration as the big guys like SuSe and Redhat.

The hooks are placed in /etc/pm/hooks/ and are just simple shell scripts. Scripts are processed in alphabetical order for suspend and hibernate and reverse alphabetical order for resume or thaw. This means they are really very simple to write and most importantly very easy to install.

pm-utils in CVS now looks very different than the original Fedora-only package, and is now a standard module suitable for any distro with all the autotools goodness. It was chosen over the ubuntu scripts as we were familar with the Redhat scripts, they were better structured, and Peter Jones was happy to maintain it externally. pm-utils is changing rapidly, so CVS is the only sane way to review the latest scripts.

As a bonus, pm-utils also provides pm-powersave, allowing us to use the same principle of small manager script, with multiple hooks for powersaving actions. For instance, a vendor could install a led script into /etc/pm/power.d/ so that a light could turn green on a new laptop model when in low power mode. At the moment, only a laptop-mode script is installed, but other scripts will be added with time.

Soon, pm-utils will be a hard dependency of HAL, so we can get rid of all the compatibility scripts in HAL, making everything that little bit more sane.

Hopefully distros will converge to this common solution, converting their custom scripts into sane pm-utils rules.

Email me with questions, or comments.