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Subject: Re: [OMPI devel] new CRS component added (criu)
From: Adrian Reber (adrian_at_[hidden])
Date: 2014-02-11 16:45:21


On Tue, Feb 11, 2014 at 08:09:35PM +0000, Jeff Squyres (jsquyres) wrote:
> On Feb 8, 2014, at 4:49 PM, Adrian Reber <adrian_at_[hidden]> wrote:
>
> >> I note you have a stray $3 at the end of your configure.m4, too (it might supposed to be $2?).
> >
> > I think I do not really understand configure.m4 and was happy to just
> > copy it from blcr. Especially what $2 and $3 mean and how they are
> > supposed to be used. I will try to simplify my configure.m4. Is there an
> > example which I can have a look at?
>
> Sorry -- been a bit busy with releasing OMPI 1.7.4 and preparing for 1.7.5...
>
> m4 is a macro language, so think of it as templates with some intelligence.
>
> $1, $2, and $3 are the "parameters" passed in to the macro. So when you do something like:
>
> AC_DEFUN([FOO], [
> echo 1 is $1
> echo 2 is $2])
>
> and you invoke that macro via
>
> FOO([hello world], [goodbye world])
>
> the generated script will contain:
>
> echo 1 is hello world
> echo 2 is goodbye world
>
> In our case, $1 is the action to execute if the package is happy / wants to build, and $2 is the action to execute if the package is unhappy / does not want to build.
>
> Meaning: we have a top-level engine that is iterating over all frameworks and components, and calling their *_CONFIG macros with appropriate $1 and $2 values that expand to actions-to-execute-if-happy / actions-to-execute-if-unhappy.
>
> Make sense?

Thanks. I also tried to understand the macros better and with the
generated output and your description I think I understand it.

Trying to simplify configure.m4 like you suggested I would change this:

    AS_IF([test "$check_crs_criu_good" != "yes"], [$2],
          [AS_IF([test ! -z "$with_criu" -a "$with_criu" != "yes"],
                 [check_crs_criu_dir="$with_criu"
                  check_crs_criu_dir_msg="$with_criu (from --with-criu)"])
           AS_IF([test ! -z "$with_criu_libdir" -a "$with_criu_libdir" != "yes"],
                 [check_crs_criu_libdir="$with_criu_libdir"
                  check_crs_criu_libdir_msg="$with_criu_libdir (from --with-criu-libdir)"])
          ])

to this:

   AS_IF([test "$check_crs_criu_good" = "yes" -a ! -z "$with_criu" -a "$with_criu" != "yes"],
         [check_crs_criu_dir="$with_criu"
          check_crs_criu_dir_msg="$with_criu (from --with-criu)"],
         [$2
          check_crs_criu_good="no"])

   AS_IF([test "$check_crs_criu_good" = "yes" -a ! -z "$with_criu_libdir" -a "$with_criu_libdir" != "yes"],
         [check_crs_criu_dir_libdir="$with_criu_libdir"
          check_crs_criu_dir_libdir_msg="$with_criu_libdir (from --with-criu)"],
         [$2
          check_crs_criu_good="no"])

correct? With three checks in one line it seems bit unreadable
and the nested AS_IF seems easier for me to understand.
Did I understand it correctly what you meant or did you
mean something else?

                Adrian