Re: [Libguestfs] [libnbd PATCH v3 19/19] socket activation: set LISTEN_FDNAMES

(4) If we pass LISTEN_PID=xxx and LISTEN_FDS=1, and rework the logic in this patch to pass LISTEN_FDNAMES="unknown" in case "h->sact_name" is NULL, then sd_listen_fds_with_names() will succeed in the nbd server, and the single returned name ("unknown") will merge into case (1), i.e., as if we had not passed (or had removed) LISTEN_FDNAMES in the environment. Therefore I propose that we implement (4). We're already populating the LISTEN_* variables ourselves (that is, not relying on systemd library or daemon logic to fill them in). I see nothing wrong with setting LISTEN_FDNAMES="unknown" ourselves; again that value is publicly specified behavior. Case (4) also appears consistent with repeated calls to sd_listen_fds_with_names(). If "unset_environment" is set to nonzero in one of those calls, then further calls will see the internal sd_listen_fds() call return 0, and behave as expected. Whereas if "unset_environment" is never set to zero in those repeated calls, then "unknown" will continue to be returned from LISTEN_FDNAMES (as if via case (1)). Under case (4), we should also update the API documentation in the previous patch ("generator: Add APIs to get/set the socket activation socket name"): > +The parameter C<socket_name> can be a short alphanumeric string. > +If it is set to the empty string (also the default when the handle > +is created) then no name is passed to the server."; we can say there, 'then the name "unknown" will be seen by the server'.