> This is pretty obviously miserable. Now you've got two > sets of policy - one at the login screen, and one in your > session. How do I ensure they're consistent?
The exact same problem happens with GDM vs. e.g. KDE PowerDevil. The settings are entirely different.
> The only sane solution is to ignore the functionality the > backend provides and have my greeter run > gnome-power-manager.
That's a GNOME-only solution and will NOT solve the problem for any other desktop. It also means GDM requires large parts of GNOME which makes it a non-starter for the Fedora KDE spin (which uses KDM instead). LightDM may or may not become a true cross-desktop solution (We'll see what Kubuntu makes of it.), but at least it is designed so that it could technically become one, unlike the entirely GNOME-centric GDM.
> It'll behave differently to your desktop
As I said, it's the same for GDM unless your desktop happens to be GNOME.
> - the range of policy you can implement will be limited > to what the daemon provides, even if your desktop > environment has a different range of features.
That's also what happens with GDM for KDE PowerDevil users, due to you dismissing its additional features as "mak[ing] no sense".
Now, unfortunately, KDM currently does not support power management at all. But running gnome-power-manager is not a cross-desktop solution for that. It does the job for GNOME users, and GNOME users only.
And by the way, another big issue is that GNOME is GDM-centric, e.g. it supports only the GDM interfaces for fast user switching whereas KDE Plasma supports both KDM's and GDM's. (This also implies that supporting GDM's interfaces will be sufficient for LightDM to interoperate with both GNOME and KDE Plasma.)
This "The display manager must match the desktop, ergo all users on the machine must use the same desktop." design needs fixing. The KDE developers do their part to support GDM, why doesn't GNOME support other DMs instead of badmouthing them?
Reusing desktop policies
> sets of policy - one at the login screen, and one in your
> session. How do I ensure they're consistent?
The exact same problem happens with GDM vs. e.g. KDE PowerDevil. The settings are entirely different.
> The only sane solution is to ignore the functionality the
> backend provides and have my greeter run
> gnome-power-manager.
That's a GNOME-only solution and will NOT solve the problem for any other desktop. It also means GDM requires large parts of GNOME which makes it a non-starter for the Fedora KDE spin (which uses KDM instead). LightDM may or may not become a true cross-desktop solution (We'll see what Kubuntu makes of it.), but at least it is designed so that it could technically become one, unlike the entirely GNOME-centric GDM.
> It'll behave differently to your desktop
As I said, it's the same for GDM unless your desktop happens to be GNOME.
> - the range of policy you can implement will be limited
> to what the daemon provides, even if your desktop
> environment has a different range of features.
That's also what happens with GDM for KDE PowerDevil users, due to you dismissing its additional features as "mak[ing] no sense".
Now, unfortunately, KDM currently does not support power management at all. But running gnome-power-manager is not a cross-desktop solution for that. It does the job for GNOME users, and GNOME users only.
And by the way, another big issue is that GNOME is GDM-centric, e.g. it supports only the GDM interfaces for fast user switching whereas KDE Plasma supports both KDM's and GDM's. (This also implies that supporting GDM's interfaces will be sufficient for LightDM to interoperate with both GNOME and KDE Plasma.)
This "The display manager must match the desktop, ergo all users on the machine must use the same desktop." design needs fixing. The KDE developers do their part to support GDM, why doesn't GNOME support other DMs instead of badmouthing them?