illumos gate

There is a note in cmd/svc/svccfg/svccfg_libscf.c to the effect that the <single_instance /> node in SMF service bundles is unimplemented and obsolete. The manual, in smf_restarter(7), says it is obsolete:

       single_instance
                          This is an optional property. When set, only one
                          instance of the service is allowed to transition to
                          an online or degraded status at any time. Note that
                          no known implementation honours this setting, and it
                          should be considered obsolete.

The language in svc.startd(8) is a bit more explicit:

       general/single_instance

           This was originally supposed to ensure that only one service
           instance could be in online or degraded state at once; however, it
           was never implemented, and is often incorrectly specified in multi-
           instance manifests. As such, it should be considered obsolete and
           not specified in new manifests.

There are a lot of manifests in the gate which still include this node, and people tend to copy-and-paste it into new things. We should:

- remove usage from all in-gate manifests
- update the DTD comments to reflect that the node is obsolete, do not use, merely ignored for backwards compatibility
- update smf_restarter(7) to stop describing what the behaviour might have been in some alternate universe, and just say it is obsolete, do not use, ignored for compatibility
- it's possible svc.startd(8) should have less commentary here and also merely say obsolete, do not use, ignored for compatibility