Re: [PATCH] clean: use warning_errno() when appropriate

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On Mon, Feb 13, 2017 at 01:53:33PM -0800, Junio C Hamano wrote:

> Jeff King <peff@xxxxxxxx> writes:
> 
> > IOW, I think this may be a case where we should be optimizing for
> > programmer time (fewer lines of code, and one less thing to worry about
> > in the callers) versus squeezing out every instruction.
> 
> Fair enough.
> 
> Unless we do the save_errno dance in all the helper functions we
> commonly use to safely stash away errno as necessary and tell
> developers that they can depend on it, the code in the patch that
> began this discussion still needs its own saved_errno dance to be
> safe, though.  I do not have a feeling that we are not there yet,
> even after we teach xmalloc() and its family to do so.

Yeah, I certainly agree that is a potential blocker. Even if it is true
today, there's nothing guaranteeing that the quote functions don't grow
a new internal detail that violates.

So in that sense doing the errno dance as close to the caller who cares
is the most _obvious_ thing, even if it isn't the shortest.

It would be nice if there was a way to annotate a function as
errno-safe, and then transitively compute which other functions were
errno-safe when they do not call any errno-unsafe function. I don't know
if any static analyzers allow that kind of custom annotation, though
(and also I wonder whether the cost/benefit of maintaining those
annotations would be worth it).

-Peff



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