Re: New module proposal: LightDM

[Brian Cameron <brian cameron oracle com>]

Robert:

I am one of the 3 GDM maintainers.  I think there is a real need for
LightDM as a FreeDesktop module, so I think it is great that LightDM
has joined the FreeDesktop family.

GDM has evolved into a display manager that is most focused on tight
integration with GNOME.  This is perfect for GNOME users and distros
that focus on GNOME users.  However, GDM is not always a good choice
for other desktop systems, distros that perhaps want to provide
multiple desktop choices and be more desktop neutral about display
management, or distros that need to support devices that may not support
things light OpenGL.

I was under the impression that a major point of the moduleset
reorganization was to allow more options and choice.  So, I think it
could also make sense for the GNOME community to be supportive of
display manager choice as well.

I am personally not sure if it makes sense for LightDM to be accepted
as a GNOME project, though.  GDM's tight integration with GNOME
Technologies makes GDM more clearly a display manager that should be
the focus of the GNOME community.  It might make more sense for LightDM
to be a GNOME module if its default greeter were GTK+ based.

At Oracle, there is a concern that GDM is becoming too tightly bound
with interfaces that are not supported by Solrais.  The recent
announcement on the ConsoleKit mailing list that there are plans to
disolve it with systemd, which is not available on Oracle, FreeBSD,
etc.  I believe one reason for this is so that GDM can better manage
device permissions when dealing with MultiSeat configurations.

http://lists.freedesktop.org/archives/consolekit/2011-May/000136.html

I think it is obviously important to Oracle to have display management
options that are not too tightly bound to things that are not supported
on Solaris like systemd, DeviceKit, PolicyKit, etc.  Also, Oracle's Sun
Ray products work best with a display manager that supports a non
OpenGL GUI.  I could imagine GDM becoming more tightly focused on
OpenGL in the future, like GNOME Shell.  Thus, perhaps LightDM could be
considered a "fallback" display manager for the GNOME community.

As an aside, I notice that Miguel de Icaza said earlier in this thread:

> May I suggest that before this is considered, a security team performs
> an audit of all the security exploits that have been attempted against
> GDM, XDM and KDM and ensure that none of those can be exploited with
> the current code base.

I am not aware of any such audit ever done in the past for any GNOME
module that has security implications (gnome-keyring, GDM, etc.).  Can
anyone provide an example of such an audit?  I very much support doing
audits like this, but why pick on LightDM about this now?

My 2 cents,

Brian


On 05/13/11 07:59 AM, Robert Ancell wrote:
> I'm proposing LightDM [1] as a replacement for GDM.  I started the
> proposal for this in GNOME 3.0 [2] but due to the young age of the
> project I thought it better to wait until 3.2 before making a full
> proposal.  This is it.  I apologise this has been done after the
> proposal period.
>
> Why replace GDM?
>
> - LightDM is a cross-platform solution.  Ubuntu is planning to switch
> to it this cycle, and other distributions have expressed interest in
> the project.  By sharing this piece of infrastructure GNOME can spend
> more time working on important GNOME components.  LightDM is aligned
> with freedesktop.org.
>
> - I am confident that the LightDM architecture is simpler than GDM.
> Some indicators of this:
>    - Smaller code size
>    - Well defined interface between greeter and session
>    - Less dependencies
>    - Less internal interfaces
>    Architecture can be a personal opinion, and I encourage those with
> programming experience to look at the code and decide for themselves.
> Note that LightDM is not lighter in features, but in architecture.
>
> - By having a well defined interface between the greeter and daemon,
> it is significantly easier to develop a greeter without knowledge of
> how display management works.  This is useful as the skillset and
> motivations of these two sets of developers are different.
>
> - LightDM is a platform for future work and is investigating the use
> of new technologies like Wayland.
>
> The details:
> Purpose:  Cross-desktop display manager
> Target: desktop
> Dependencies: libglib, libpam, libxdmcp, libxcb, libxklavier,
> gobject-introspection, libgtk+
> Resource Usage: Launchpad for source control and bug tracking [1],
> tarballs in public ftp [3] (in process of moving to freedesktop.org)
> Adoption: Accepted for use in Ubuntu 11.10, interest from other distributions
> GNOME-ness: Display manager is cross-desktop, example GTK+ greeter is
> fully GNOME compliant.  I would recommend this module is maintained in
> the GNOME servers to get all the build and translation support.
> 3.0 readiness: GTK greeter currently using GTK2, but all other code
> uses latest GNOME standards.
> License: GPL3
>
> [1] https://launchpad.net/lightdm
> [2] https://mail.gnome.org/archives/desktop-devel-list/2010-October/msg00226.html
> [3] http://people.ubuntu.com/~robert-ancell/lightdm/releases/
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