[SSSD] Design Discussion: Domains, users and groups over D-Bus

Jakub Hrozek jhrozek at redhat.com
Thu Jan 8 09:05:10 UTC 2015


On Wed, Jan 07, 2015 at 03:41:01PM -0500, Simo Sorce wrote:
> On Wed, 07 Jan 2015 15:25:30 -0500
> Dmitri Pal <dpal at redhat.com> wrote:
> 
> > On 01/07/2015 03:05 PM, Simo Sorce wrote:
> > > On Tue, 06 Jan 2015 09:59:08 -0500
> > > Dmitri Pal <dpal at redhat.com> wrote:
> > >
> > >> On 01/06/2015 05:54 AM, Jakub Hrozek wrote:
> > >>> On Tue, Jan 06, 2015 at 11:31:55AM +0100, Pavel Březina wrote:
> > >>>>>> *Users*
> > >>>>>> Do we want also to have methods ListDomainUsers() and
> > >>>>>> ListUsers() without the name filter?
> > >>>>> To list all? What about using '*' for that?
> > >>>> We can implement it this way internally, but exposing an easier
> > >>>> way to the consumers is nice, imho.
> > >>> I'm not too opposed, although I prefer minimal APIs.
> > >>>
> > >>>> However, do we actually want to allow to list all users? As
> > >>>> Dmitri suggested we may want to require the minimum filter
> > >>>> length since the number of users may be very high. The maximum
> > >>>> D-Bus message is 128MiB so I think we are good there but I think
> > >>>> it can be very time consuming to return all users without some
> > >>>> sort of paging.
> > >>> This feature is internally dependant on enumerate=true, where we
> > >>> already store all standard POSIX attributes (struct passwd, struct
> > >>> group) in-memory, do you think the D-Bus "enumeration" provides
> > >>> that much overhead?
> > >>>
> > >>> Paging would be really complex, we'd need to store the full
> > >>> results in-memory per-client anyway and then pass around some
> > >>> kind of cookie to resume iteration..
> > >>>
> > >>> In a centralized environment, I wouldn't expect the listing
> > >>> commands to be used that commonly. Greeters or login managers
> > >>> (gdm) would typically use the cached users instead. Some
> > >>> applications (Hi, RHEV-M!) choose to display all their users in
> > >>> some kind of table and then I would expect them to implement
> > >>> paging themselves:
> > >>>
> > >>> for letter in a..z:
> > >>>       users = ListUsersByNameFilter($letter)
> > >>>
> > >>>>>> Do we want some other filter options as well?
> > >>>>> In the design I wanted to keep the filtering simple. Unless we
> > >>>>> receive some other requirements..
> > >>>> Yes, you suggested to allow only asterisk. Implement full regular
> > >>>> expression efficiently as Dmitri would be quite problematic since
> > >>>> ldb doesn't support regex lookup thus we would have to do this
> > >>>> ourselves and therefore we would loose indices, or am I wrong?
> > >>> I guess we'd have to grab all the entries and filter them
> > >>> ourselves..
> > >>>
> > >>> (Yes, this is the reason I chose the asterisk notation in the
> > >>> first place) _______________________________________________
> > >>> sssd-devel mailing list
> > >>> sssd-devel at lists.fedorahosted.org
> > >>> https://lists.fedorahosted.org/mailman/listinfo/sssd-devel
> > >> Several points:
> > >>
> > >> - IMO having a full regular expression support will be an overhead.
> > >> - "Begins with" filtering with * to indicate the remaining part is
> > >> good enough
> > > reasonable
> > >
> > >> - I do not think we should rely on enumeration. I think we should
> > >> do a lookup since these operations will be rare.
> > > Nope.
> > > This is the same thinking the implementers of the nss interface went
> > > through. And then users started using enumeration all the time.
> > >
> > > It may be ok to let users programmatically force full enumeration
> > > somehow. But the default should be to return only what is in cache.
> > > If you do otherwise people will test applications using * with 3
> > > users on the system and then fail spectacularly when there are
> > > actually 100K users in the directory.
> > 
> > I think there is a problem with the approach you suggest.
> > 
> > Say there is an application that allows you to list groups starting
> > with a letter. It is used to define roles for application
> > administration.
> > 
> > Assume that there is a group "Agroup". It is a new group that does
> > not have users yet. But it was created for use with the application
> > so that roles can be associated with this group. The admin of the
> > application thus wants to start using it.
> > This group will never be looked up if "A*" query will be run against 
> > cache because it will not end up in cache. That would force admin to 
> > turn full enumeration on SSSD. This is bad.
> 
> What matters is the '*' does not do enumeration, if 'ABC*' causes an
> online lookup it is fine imo.

Yes, this is exactly what I was proposing. However, handling 'ABC*' on
the back end side must be implemented, currently we only handle a single
entry or enumeration.

I might have confused you because I proposed to first finish the DBus
*responder* work and temporarily require enumeration until we extend the
back end.

I hope it makes sense now.



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