[oe] overriding tasks with EXPORT_FUNCTIONS

[Robert P. J. Day]

On Mon, 14 Jul 2014, Paul Eggleton wrote:

> Hi Robert,
>
> On Sunday 13 July 2014 10:19:08 Robert P. J. Day wrote:
> >   followup to last post -- all of the methods for "overriding" task
> > definitions in the last post can be used without predeclaring that
> > you're about to do that; you just go ahead and do it in either a class
> > file or a recipe file. on the other hand, EXPORT_FUNCTIONS allows you
> > to retain the base definition of a task (or non-task function, as i
> > read it), then define a more general enhanced version.
> >
> >   (side note: i don't see a single mention of "EXPORT_FUNCTIONS" in
> > any of the numerous yocto docs -- i think this feature needs some
> > explanation *somewhere*. :-)
>
> Did you try the new BitBake manual?
>
> http://www.yoctoproject.org/docs/current/bitbake-user-manual/bitbake-user-manual.html#flexible-inheritance-for-class-functions
>
> Let me know if that doesn't answer your questions.

  i think that section could be extended a bit to offer more
information, so i might take a shot at it. first, i think it should
emphasize that it's primarily(?) used for enhancing the default
implementation of "base" functions. just using "foo" and "bar" here is
maddeningly vague. throwing in an (admittedly OE-related) example like
this from cmake.bbclass:

  cmake_do_compile()  {
        cd ${B}
        base_do_compile
  }

  cmake_do_install() {
        cd ${B}
        autotools_do_install
  }

would, i think, clarify the general power of this feature.

  and a question about a particular example. richard purdie replied to
my post a while back about package.bbclass and debian.bbclass, but i'm
still a bit confused. here's a snippet from package.bbclass:

  python package_package_name_hook() {
      """
      A package_name_hook function can be used to rewrite the package names by
      changing PKG.  For an example, see debian.bbclass.
      """
      pass
  }
  EXPORT_FUNCTIONS package_name_hook

so as i read it, the above defines the function
"package_package_name_hook" which doesn't do a whole lot, but is now
available to other classes that inherit this one, particularly
debian.bbclass that's specifically mentioned.

  but if one goes to debian.bbclass, one finds:

  python debian_package_name_hook () {
      import glob, copy, stat, errno, re
      ... snip ...
  }

  EXPORT_FUNCTIONS package_name_hook

but, as far as i can tell, that is the only class that requires a
package name hook, and it simply defines its own implementation -- it
does nothing with package.bbclass and makes no reference to the
exported function package_package_name_hook(). so am i just
misunderstanding something? what was the point of defining and
exporting that function in package.bbclass if no other class takes
advantage of it?

rday

-- 

========================================================================
Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
LinkedIn:                               http://ca.linkedin.com/in/rpjday
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