Re: CustomScan support on readfuncs.c

> On Mon, Sep 28, 2015 at 8:31 PM, Kouhei Kaigai <kaigai@ak.jp.nec.com> wrote:
> >> Instead of doing this:
> >>
> >> +    /* Dump library and symbol name instead of raw pointer */
> >>      appendStringInfoString(str, " :methods ");
> >> -    _outToken(str, node->methods->CustomName);
> >> +    _outToken(str, node->methods->methods_library_name);
> >> +    appendStringInfoChar(str, ' ');
> >> +    _outToken(str, node->methods->methods_symbol_name);
> >>
> >> Suppose we just make library_name and symbol_name fields in the node
> >> itself, that are dumped and loaded like any others.
> >>
> >> Would that be better?
> >>
> > I have no preference here.
> >
> > Even if we dump library_name/symbol_name as if field in CustomScan,
> > not CustomScanMethods, in a similar way, we cannot use WRITE_STRING_FIELD
> > here, because its 'fldname' assumes these members are direct field of
> > CustomScan.
> >
> >   /* Write a character-string (possibly NULL) field */
> >   #define WRITE_STRING_FIELD(fldname) \
> >       (appendStringInfo(str, " :" CppAsString(fldname) " "), \
> >        _outToken(str, node->fldname))
> 
> Well that's exactly what I was suggesting: making them a direct field
> of CustomScan.
>
Let me confirm. Are you suggesting to have library_name/symbol_name
in CustomScan, not CustomScanMethods?
I prefer these fields are in CustomScanMethods because we don't need
to setup them again once PG_init set up these symbols. CustomScan has
to be created every time when it is chosen by planner.

> > One other question I have. Do we have a portable way to lookup
> > a pair of library and symbol by address?
> > Glibc has dladdr() functions that returns these information,
> > however, manpage warned it is not defined by POSIX.
> > If we would be able to have any portable way, it may make the
> > interface simpler.
> 
> Yes: load_external_function.
>
It looks up an address by a pair of library and symbol name....
What I'm looking for is a portable function that looks up a pair
of library and symbol name by an address, like dladdr() of glibc.
I don't know whether other *nix or windows have these infrastructure.

Thanks,
--
NEC Business Creation Division / PG-Strom Project
KaiGai Kohei <kaigai@ak.jp.nec.com>