Re: (ITS#7182) back-ldap monitoring improvements

[masarati@aero.polimi.it]

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> On 04/04/2012 03:26 PM, hyc@symas.com wrote:
>> See ITS#7225.
>>
>> Even after the SEGV is patched, the pcache slapd fails to start in
>> test020
>> because the monitor calls are unable to register their entries.
>> Something is
>> wrong in your initialization code.
>
> When the ldap database is opened before the monitor, all registration is
> deferred and fake OK status is returned. Then, while the subsystems are
> initializing, the new subsystems (that have to derive their DN from
> something) do not yet have access to the DN of the database monitor
> entry (even though it may already exist). Only after all subsystems have
> been opened does the deferred database registration proceed, but by then
> there is no way to notify anyone that the DN has been published. Thus we
> are left with a chicken-and-egg problem.
>
> One way out of this I currently see is providing a register_database
> callback that is called immediately when no deferring takes place or
> immediately after the entry in limbo_queue has been processed. This way
> once the DN information is ready, the subsystem registration can start
> safely.
>
> There is an alternative, adding a defferable monitor_subsys registration
> (and alimbo entry type) that, if monitor is not opened, takes place in
> the second phase (roughly at the same time as above).
>
> There are aspects in which either one is cleaner, whereas the other one
> can backfire/clutter the API and vice versa for others. I have not
> decided yet.
>
>> Also, you're using monitor_entry_stub() directly in the back-ldap code.
>> It is
>> forbidden for modules to directly reference each other's symbols. If you
>> need
>> this function, add it to monitor_extra_t first and call it through
>> there.
>
> Thank you, I will. And sorry for breaking master with this ITS.

I think the problem (and the patch) can be greatly simplified and made
clearer by totally eliminating the addition of a subsystem.  All you need
is to add to either the database entry (when back-ldap is a database) or
to the overlay entry (when back-ldap is wrapped by one of the many
overlays built on top of it) a couple of entries that play the role of
roots of the connections and operations entries.  The creation of these
entries can be deferred if the parent entries do not exist yet.  The one
related to connections can take care of creating volatile children.  The
ones related to operations can have specific callbacks, and the parent
entry can have a callback that creates the children when they do not exist
yet.  I'm trying to work out a fix for it.

p.

p.