[U-Boot] [PATCH v3 0/16] Provide a mechanism to avoid using #ifdef everywhere

[Tom Rini]

On Tue, May 14, 2013 at 03:22:04PM -0700, Vadim Bendebury wrote:
> On Tue, May 14, 2013 at 3:15 PM, Tom Rini <trini at ti.com> wrote:
> > On Tue, May 14, 2013 at 02:27:32PM -0700, Simon Glass wrote:
> >> Hi Tom,
> >>
> >> On Tue, May 14, 2013 at 2:21 PM, Tom Rini <trini at ti.com> wrote:
> >> > On Mon, May 13, 2013 at 03:12:07PM -0700, Simon Glass wrote:
> >> >> Hi Tom,
> >> >>
> >> >> On Thu, Mar 21, 2013 at 7:38 AM, Tom Rini <trini at ti.com> wrote:
> >> >> > On Tue, Feb 26, 2013 at 08:10:53AM -0800, Simon Glass wrote:
> >> >> >
> >> >> >> Many parts of the U-Boot code base are sprinkled with #ifdefs. This makes
> >> >> >> different boards compile different versions of the source code, meaning
> >> >> >> that we must build all boards to check for failures. It is easy to misspell
> >> >> >> an #ifdef and there is not as much checking of this by the compiler. Multiple
> >> >> >> dependent #ifdefs are harder to do than with if..then..else. Variable
> >> >> >> declarations must be #idefed as well as the code that uses them, often much
> >> >> >> later in the file/function. #ifdef indents don't match code indents and
> >> >> >> have their own separate indent feature. Overall, excessive use of #idef
> >> >> >> hurts readability and makes the code harder to modify and refactor. For
> >> >> >> people coming newly into the code base, #ifdefs can be a big barrier.
> >> >> >>
> >> >> >> The use of #ifdef in U-Boot has possibly got a little out of hand. In an
> >> >> >> attempt to turn the tide, this series includes a patch which provides a way
> >> >> >> to make CONFIG macros available to C code without using the preprocessor.
> >> >> >> This makes it possible to use standard C conditional features such as
> >> >> >> if/then instead of #ifdef. A README update exhorts compliance.
> >> >> >
> >> >> > OK, this is true.  Looking over the series, a number of the patches are
> >> >> > just general fixes / improvements that don't depend on the autoconf_...
> >> >> > work.  Lets split this out now and take them in now as they seem like
> >> >> > reviewable by inspection code.
> >> >>
> >> >> Well sorry I didn't make time to get this done last time. I can do
> >> >> this now or...
> >> >>
> >> >> >
> >> >> > For the approach itself, I'm not sure which is best here.  In a lot of
> >> >> > cases we're trading an #ifdef for adding a level of indent to already
> >> >> > pretty indented code and that feels like a wash, in terms of readability
> >> >> > to me.  We probably need to re-factor some of the code in question there
> >> >> > too for readability, then see about using autoconf_... type things, or
> >> >> > maybe something else.
> >> >>
> >> >> I think you are saying to do the rearrangement and clean-up first,
> >> >> then add autoconf afterwards. I can do that but really I am wondering
> >> >> what you think of the autoconf concept? The Kconfig stuff is related
> >> >> here too, but first I would like to decide on what to do with the
> >> >> #ifdefs.
> >> >
> >> > I think a lot of our #ifdefery is a problem of code that's in need of
> >> > some love and re-org and cleaning and updating.  One of the old style
> >> > rules I still try and follow is that after a few levels of indent code
> >> > doesn't read well.  Also big nested #ifdefs don't read well.  So we're
> >> > trading one in for the other.  But your series showed a lot of places
> >> > where we can re-factor things to improve readability.  So lets go that
> >> > way.  Then we can see if there's still things to improve on, and what
> >> > dead code we still have around.
> >>
> >> So are you saying that you are keen on the autoconf idea?
> >
> > I'm saying lets clean up the code and see if we still need something
> > like autoconf.  It seems to provide the most benefit in terms of
> > readability in places that could read a lot better with some clean up
> > and refactoring before we add new tools to the pile.
> >
> 
> Yet another great advantage of autoconf is that it ensures a
> consistent combination of the configuration options, with the status
> quo it is so easy to make a mistake and create a deficient
> configuration.

There are things I like about the concept, but I really want to see the
problem areas in question made more readable as it will both help in
general, and if we do make this conversion later, make the conversion
easier as we'll hopefully kill off some of the nested and tricky ifdefs.

-- 
Tom
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