at present, libscf supports transactions at the property group level, via scf_transaction_create (3SCF) and friends. for the NWAM project, we would like to support transactions that may span multiple property groups, and would like to be able to load/commit an entire SMF instance if possible (to support renaming of instances representing datalinks or IP interfaces). at present, we're getting by with a combination of the following mechanisms, but maybe there's a better/simpler approach we haven't thought of?
1: we use fcntl(2)-based lockfiles to protect multiple consumers from colliding during commit (a system-wide mechanism is needed, since the consumers may be different processes, e.g. nwamcfg vs the NWAM GUI). 2: we always load from a dedicated snapshot (the "nwam" snapshot), which is taken after a successful commit, and as such represents completely committed data for the instance. 3: on loading data for the instance, we store the "scf_propertygroup_t *", and use it at commit time. this ensures that if the propertygroup has been touched since load time, the scf_transaction_commit (3SCF) action will fail, returning 0. this allows us to avoid lost updates - if the editing snapshot has been updated since load, the commit action will fail for the property group in question. 4: if commit succeeds, we refresh the instance and take the "nwam" snapshot, since we now have a new "last good config". these mechanisms combine to ensure that loaded data has always been fully commited (since the dedicated "nwam" snapshot is only taken after all property groups have been committed), that multiple commits cannot collide (via fcntl locking), and that we do not experience lost updates (via the use of the property group handle which we store at load time and reuse at commit). however it all seems like a bit of a hodge-podge, and maybe there's a better way to tackle all of this. it occurs to me that if it were possible to atomically roll back the editing snapshot as a whole to a previously-taken, "last good config" snapshot, instance-level transactions would be a cinch, but i don't know if that is feasible. any advice or suggestions would be greatly appreciated. thanks! alan
