Re: [musl] [PATCH v3 2/2] nftw: implement FTW_ACTIONRETVAL (GNU extension)

[Ismael Luceno <ismael@iodev.co.uk>]

On 24/Jan/2022 09:47, Dominique MARTINET wrote:
> This didn't get much traction when I submitted one last year:
> https://www.openwall.com/lists/musl/2021/03/26/1
> (and there were at least a couple other occurences I could find at the
> time)

Thanks for reviewing. I was unaware of your submission.

> But given it keeps getting resubmitted I assume we can say that confirms
> there's demand for it?
<...> 
> > @@ -72,12 +72,19 @@ static int do_nftw(char *path, int (*fn)(const char *, const struct stat *, int,
> >  		if (!fd_limit) close(dfd);
> >  	}
> >  
> > -	if (!(flags & FTW_DEPTH) && (r=fn(path, &st, type, &lev)))
> > -		return r;
> > +	r = 0;
> > +	if (!(flags & FTW_DEPTH) && (r=fn(path, &st, type, &lev))) {
> > +		if ((flags & FTW_ACTIONRETVAL)) {
> > +			if (r == FTW_STOP) return FTW_STOP;
> > +			if (r == FTW_SKIP_SUBTREE) return 0;
> > +			/* other values are saved for when returning */
> 
> Hm, I'd naively think you would want to return immediately the other
> values as well, so the else below is wrong?
> But I didn't take long enough to check what e.g. a SKIP_SIBLINGS would
> mean here, the construction just looks a bit odd to me.

SKIP_SIBLINGS doesn't imply SKIP_SUBTREE, so must be saved and returned
when finishing.

> > @@ -120,10 +130,13 @@ static int do_nftw(char *path, int (*fn)(const char *, const struct stat *, int,
> >  	}
> >  
> >  	path[l] = 0;
> > -	if ((flags & FTW_DEPTH) && (r=fn(path, &st, type, &lev)))
> > -		return r;
> > -
> > -	return 0;
> > +	if (flags & FTW_DEPTH) {
> > +		r = fn(path, &st, type, &lev);
> > +		/* ignore FTW_SKIP_SUBTREE (too late), the caller is broken */
> > +		if ((flags & FTW_ACTIONRETVAL) && r == FTW_SKIP_SUBTREE)
> > +			return 0;
> 
> IIRC the glibc implementation also ignores FTW_SKIP_SIBLINGS in that
> case (nftw returns 0), I'm not sure how much of a 1-to-1 implementation
> we want -- I had implemented my version through a black-box approach
> with a client exercising all kind of different code paths as for a gnu
> extension I'd assume glibc to be the reference.

FTW_SKIP_SUBTREE makes no sense with FTW_DEPTH, but FTW_SKIP_SIBLINGS
works with both.