Messages in this thread | | | Date | Mon, 9 Jul 2018 16:30:01 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] kernel.h: Add for_each_if() |
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On Mon, 9 Jul 2018 18:25:09 +0200 Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> To avoid compilers complainig about ambigious else blocks when putting > an if condition into a for_each macro one needs to invert the > condition and add a dummy else. We have a nice little convenience > macro for that in drm headers, let's move it out. Subsequent patches > will roll it out to other places. > > The issue the compilers complain about are nested if with an else > block and no {} to disambiguate which if the else belongs to. The C > standard is clear, but in practice people forget: > > if (foo) > if (bar) > /* something */ > else > /* something else
um, yeah, don't do that. Kernel coding style is very much to do
if (foo) { if (bar) /* something */ else /* something else }
And if not doing that generates a warning then, well, do that.
> The same can happen in a for_each macro when it also contains an if > condition at the end, except the compiler message is now really > confusing since there's only 1 if: > > for_each_something() > if (bar) > /* something */ > else > /* something else > > The for_each_if() macro, by inverting the condition and adding an > else, avoids the compiler warning.
Ditto.
> Motivated by a discussion with Andy and Yisheng, who want to add > another for_each_macro which would benefit from for_each_if() instead > of hand-rolling it.
Ditto.
> v2: Explain a bit better what this is good for, after the discussion > with Peter Z.
Presumably the above was discussed in whatever-thread-that-was.
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