Re: [Tracker] Migrating tracker from HAL to DeviceKit

[Jamie McCracken <jamie mccrack googlemail com>]

Hi richard,

ïTracker does indeed use HAL for power management and for detecting
removable storage

As HAL support is optional (not all platforms have HAL like solaris) it
would probably make sense to switch to a raw dbus solution 

the only sang at this stage is which distro's use Device kit? I dont
believe jaunty uses it?

Ergo at this point in time, it might be best to see if device-kit is
activated on dbus and use it if its there else fallback to HAL.

In the long run we can then remove HAL support

martyn, do you agree?

jamie


On Wed, 2009-04-01 at 14:23 +0100, Richard Hughes wrote:
> Hey list,
>
> (some background, I'm a developer for HAL, and the maintainer of
> DeviceKit-power, PackageKit and gnome-power-manager)
>
> Some of you may already know, HAL is a dying beast upstream.
> Unfortunately, it's a widely used[1] beast, and it's my job to try and
> convert applications to DeviceKit-power and DeviceKit-disks so they
> continue to work when bits of HAL slowly get switched off.
>
> I've been reviewing the tracker source code, and there appears to be two
> main points of HAL integration with tracker, the storage code and the
> power management code.
>
> Obviously the former can be migrated to DeviceKit-disks, and the latter
> to DeviceKit-power. I'll concentrate on the latter for now.
>
> I notice the code is set up to enumerate batteries and ac_adapters, and
> to make a policy decision about whether a computer is on mains power
> based on that. Unfortunately, it fails to filter non-primary batteries
> and the charged logic seems very fragile. It also exports percentage and
> exists data which seems to break pretty hard with multiple batteries, or
> where batteries are not present, but exported to the system.
>
> I assume you are making policy decisions based on the percentage and
> battery discharging attributes. This is all handled much better in
> DeviceKit-power, as it's been designed from the ground up for other
> frameworks and applications to use, rather than just a bare device tree
> with methods like HAL was.
>
> In the interface spec[2] you can see there are two public properties
> exposed over DBus:
>
> 'on-battery'     read      'b'
> 'on-low-battery' read      'b'
>
> This has all the correct logic encoding in DeviceKit-power, so we don't
> do things like set on-battery when we're running with a wireless-mouse
> connected, or set on-low-battery when we've just inserted a second
> battery at 0%.
>
> So, would it be permissible to convert the HAL power management parts in
> tracker to use DeviceKit-power? I would be willing to do the work, with
> your permission. I can either use the new devkit-power-gobject library,
> or just use plain dbus-glib. The advantage of the latter is that it
> "just works" if tracker is being used on a system that does have support
> for DeviceKit (e.g. < Fedora 10).
>
> Thanks,
>
> Richard Hughes
>
> [1] http://fedoraproject.org/wiki/Features/DeviceKit/HalDependencies
> [2] http://hal.freedesktop.org/docs/DeviceKit-power/Power.html
>
>
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