Hi Neels,
On Tue, Jan 22, 2019 at 03:00:31AM +0100, Neels Hofmeyr wrote:
I think we all agree that what happened with the msgb_wrap_with_TL() is a prime example about how absolutely *not* to do things. This makes me want to rewrite libosmocore history.
I had the same feeling yesterday. To clarify "rewrite libosmocore git history" is probably what you hinted here :)
Let's try to avoid this kind of series of events in the future.
- Separate function definitions must not have identical names.
- This applies both to the master HEADs as well as throughout entire API history.
- Especially functions moved to another source tree *must* change their name.
This is generally what we do. And "generally", we prefix them with osmo_ in the libraries, and don't permit the osmo_ prefix for symbols in applications. However, the msgb_ code pre-dates the osmo_ prefix - it even predates the name Osmocom as the project name.
So we have some legacy prefixes that are "reserved" for use in libosmo*. Those are
bitvec_ gsmtap_ log_ msgb_ rate_ctr_ abis_nm_ gprs_cipher_ gsm0341_ gsm0480_ gsm0502_ gsm0503_ gsm0808_ gsm29118_ gsm0858_ gsm340_ gsm411_ gsm414_ gsm48_ gsm610_ gsm620_ gsm690_ gsm_7bit_ lapd_ lapdm_ milenage_ rsl_ rxlev_ tlv_ ipa_ccm bssgp_ gprs_ns_ gprs_nsvc_ btsctx_ osim_ vty_ vector_ telnet_ config_ cmd_ buffer_
Unfortunately a lot of them are rather generic, so it's hard to avoid, at least in absence of any automatic tests for it. It's a separate discussion whether we should e.g. stop to export los of libosmovty internals (buffer, vector, cmd) - and if we should prefix all symbols in libosmo* with osmo_* providing the older names only as backwards compatibility layer with possibly weak symbols to be able to migrate to a cleaner namespace at least at some point in the future.
Furthermore, there is one factors that made this particular instance even more problematic:
The respective functions were inline functions. Otherwise we could have simply turned the library symbol into a weak symbol, making any application implementation supersede the library one.
- Such API changes in libosmocore should be tested with "all" depending programs.
ACK. So what's needed is some kind of build job that continuously builds old applications against modern libosmo*. This could be run at least once per day/night, so we get notified if we introduce any such breakage and can fix libosmo* shortly to keep the incompatiblity something that appeared for a few days in the history, at maximum.
- API fixes in libosmocore should ideally build with both past and future versions of depending source trees, i.e. should not need a matching patch in the other source trees.
That goes without saying. It just wasn't possible in this case.
Regards, Harald