OAP depends on libgtp? (openbsc:6cacc56d)

historical

Hi!

On Mon, Jan 18, 2016 at 11:09:35AM +0100, Neels Hofmeyr wrote:
> about your commit on openbsc, merged as 6cacc56d: libgtp should not be a
> prerequisite for OAP. OAP is a rather simple protocol built on an IPA
> connection and doesn't really relate to GTP at all.
> 
> So if your build of OAP was dependent on libgtp, that's a bug, and
> probably my fault.
> 
> Could you please verify / indicate the failure you saw so we/I can fix 
> it?

I just revisited the situation.
The tests in tests/oap are either way only built when both LIBCARES and 
LIBGTP are present because of the clause in tests/Makefile.am.
At this point I cannot reconstruct how exactly I came up with this 
patch.
I think that conditional in tests/Makefile.am is there because of the 
similar conditional in src/gprs.
osmo-sgsn only gets built when those two libraries are present.
src/gprs/oap.o is a dependency of only osmo-sgsn.
When the tests in tests/oap are built unconditionally, but osmo-sgsn 
wasn't built before because of a missing dependency, that fails with:

        make[3]: Entering directory '/home/blackbit/src/telco/osmo/openbsc/openbsc/tests/oap'
          CC       ../../src/gprs/oap.o
        ../../src/gprs/oap.c:256:1: fatal error: opening dependency file .deps/../../src/gprs/oap.Tpo: No such file or directory
         }
         ^
        compilation terminated.
        Makefile:375: recipe for target '../../src/gprs/oap.o' failed
        make[3]: *** [../../src/gprs/oap.o] Error 1

oap.o isn't built in this case if it is needed, it is pulled in with 
LDADD.

So, whether oap is built currently is indirectly dependent on the 
presence of LIBCARES and LIBGTP, but the patch would not have been 
needed, because of the conditional in tests/Makefile.am.

It's all a bit ocnfusing :-)

Interestingly, while digging around I found a different minor issue in 
the buildsystem that is only visible when the dependencies are installed 
in distinct directories. It's surprising that I didn't stumble upon that 
initially. I'll send a seperate patch for that.

Kind regards,
-Alex
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