Re: SCCP connection identifiers vs. local references

On Wed, Mar 20, 2019 at 08:22:35AM +0100, Harald Welte wrote: Ah. So the proper solution is to be fine with "collisions" because local reference and SAP conn id are distinct number spaces. Ok, but... I know you will probably roll your eyes at least once when reading this mail, and I sympathise, but please bear with me so I can figure out what exactly osmo-msc should do about outgoing SAP conn_id... For me there is still a disconnect in the reasoning. In short, whoever invents SAP conn ids should invent them for both directions. (Nevermind local-reference, only talking SAP conn ID.) In long: Let's focus on that last stage alone, as close as it gets to the message consumer: a) remote peer sends a N-CONNECT. "Things happen" in SCCP, then in the end: libosmo-sccp dispatches me a struct osmo_scu_prim. prim.connect.conn_id contains a number, the SAP connection ID. b) I send an N-CONNECT. I compose an osmo_scu_prim. I put in prim.connect.conn_id a number, the SAP connection ID. "Things happen" to send SCCP. If these SAP conn_ids are of the same number space for incoming and outgoing osmo_scu_prim, which I assume, then why not provide the caller of the SAP API, in that first stage that actually dispatches/receives the struct osmo_scu_prim locally, nevermind the SCCP wiring happening further away, with one common API function to determine an unused local SAP conn_id? [----------osmo-program-----------] SCCP provider SAP API message handler ---------local-ref-----> black --conn_id-> <--------local-ref------ box <-conn_id-- ^ get_unused_sap_conn_id() Am I getting this picture correctly? (ignoring that currently the SCCP provider is also in the same program, incidentally.) That layer violating patch of mine was made from an angle of: "this osmo_user_sap API has to know which struct osmo_scu_prim.*.conn_id already exist, nevermind how they are made. Even if we separate local ref and conn_id later, the knowledge about used conn_ids will still be in this first stage, and the caller should still ask the osmo_user_sap API for an unused SAP conn_id instead of iterating its own object lists." Shouldn't be too hard to separate the SAP conn ID scope from the local-reference scope in libosmo-sccp, if that is needed to allow this in a correct way. Otherwise we only push the mistake into osmo-{bsc,msc} code. Thanks ~N