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Re: [Qemu-block] [Qemu-devel] [PATCH] error: Remove NULL checks on error

From: Eduardo Habkost
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH] error: Remove NULL checks on error_propagate() calls
Date: Thu, 9 Jun 2016 17:21:12 -0300
User-agent: Mutt/1.6.1 (2016-04-27)

On Thu, Jun 09, 2016 at 02:11:23PM -0600, Eric Blake wrote:
> On 06/09/2016 01:50 PM, Eduardo Habkost wrote:
> > On Thu, Jun 09, 2016 at 01:37:23PM -0600, Eric Blake wrote:
> > [...]
> >>
> >> Hmm - it seems like in most of the cases where the ONLY thing done in
> >> the if (local_err) block is to propagate the error, we should instead be
> >> directly assigning to errp instead of wasting a local variable.  At this
> >> point, my review is repetitive enough that I'll stop looking, and leave
> >> it up to you and Markus whether to attempt a more ambitious Coccinelle
> >> script.
> > 
> > If it happens immediately before the function end or a return
> > statement it should be easy, but it would still require some
> > manual work to remove the unused variable declaration. Probably
> > easier to do that in a follow-up patch.
> I think Coccinelle can be used to eliminate unused local variables, but
> don't know the recipe off-hand; maybe a web search will turn up something?

I found something called "when constraints", but the
documentation isn't very clear.

There's an example here:

> > 
> > It's harder (impossible?) to make Coccinelle avoid matching if
> > local_err is used somewhere else in the function. But it's
> > probably doable with some manual work, in a follow-up patch.
> I don't know - Coccinelle is rather powerful, and there may indeed be a
> way to flag conditions for a variable that is not used anywhere except
> in the lines mentioned in the recipe, vs. a variable that can also be
> used in the ... portion of the recipe.

I found a hackish way to do that. Sending a follow-up patch in 1


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