bin/182098: [patch] Change kldxref fts_open ordering so it produces a consistent linker.hints between machines of the same architecture.

[Derek Schrock]

The following reply was made to PR bin/182098; it has been noted by GNATS.

From: Derek Schrock <dereks at lifeofadishwasher.com>
To: Jilles Tjoelker <jilles at stack.nl>
Cc: bug-followup at FreeBSD.org
Subject: Re: bin/182098: [patch] Change kldxref fts_open ordering so it
 produces a consistent linker.hints between machines of the same
 architecture.
Date: Sat, 28 Sep 2013 16:50:10 -0400

 Ok I see what you mean by using FTS_D.  Everything looks good to me, I
 compared the linker.hints generated by the two system from
 
 On Sat, Sep 28, 2013 at 08:39:53PM +0200, Jilles Tjoelker wrote:
 > On Tue, Sep 24, 2013 at 09:32:42PM -0400, Derek Schrock wrote:
 > > On Mon, Sep 16, 2013 at 12:39:58AM +0200, Jilles Tjoelker wrote:
 > > > In the interest of reproducible builds, your patch seems a good idea. It
 > > > seems unattractive to run kldxref /boot/kernel on every machine.
 > > > 
 > > > The implementation of compare() seems unnecessarily complex though. In
 > > > find -s, the fts_names are simply passed to strcoll() (here, strcmp()
 > > > would be better). The trickery with the length may cause inconsistent
 > > > results if one filename is a prefix of another (rare).
 > 
 > > Fair enough after reading more of the fts(3) man fts_name is always
 > > null terminated.
 > 
 > > > This change may also expose a latent bug with kldxref -R: it does not
 > > > work properly if a directory contains both files that need a mention in
 > > > a hints file and subdirectories, and at least one such file appears
 > > > after a subdirectory. Because your change alters the traversal order, it
 > > > might break a use of kldxref -R that previously happened to work. You
 > > > can make it work reliably by sorting FTS_D entries after other entries.
 > 
 > > Yep, after some additional testing with the patched kldxref it
 > > produced different linker.hints files. 
 > 
 > Hmm, that is unexpected. The sorting happens on entries of each
 > directory, and find -s does the same.
 > 
 > > The new patch uses fts_parent's fts_name (the directory's name).
 > > First compare the parent's name, if the same compare the passed
 > > FTSENTs.
 > 
 > The comparison on the parent's name seems redundant due to the way
 > fts(3) does the sorting.
 > 
 > I tried my idea using FTS_D.
 > 
 > Here is a script to test kldxref on this:
 > 
 > #!/bin/sh
 > 
 > kldxref=${1:-kldxref}
 > kldxrefpath=$(command -v "$kldxref" 2>/dev/null) || {
 > 	printf "%s not found\n" "$kldxref"
 > 	exit
 > }
 > printf "Testing %s\n" "$kldxrefpath"
 > tmpdir=$(mktemp -d -t kldxreftest) || exit
 > cd "$tmpdir" || exit
 > cp /boot/kernel/if_re.ko . || exit
 > mkdir subdir1 || exit
 > cp /boot/kernel/if_faith.ko . || exit
 > cp /boot/kernel/zlib.ko . || exit
 > cp /boot/kernel/unionfs.ko subdir1 || exit
 > printf "Directory structure created in %s\n" "$tmpdir"
 > "$kldxref" -R "$tmpdir"
 > mainstrings=$(strings linker.hints)
 > subdir1strings=$(strings subdir1/linker.hints)
 > bad=
 > for m in if_re.ko if_faith.ko zlib.ko; do
 > 	case $mainstrings in
 > 	*"$m"*) ;;
 > 	*) printf "%s is missing from main\n" "$m"; bad=1 ;;
 > 	esac
 > 	case $subdir1strings in
 > 	*"$m"*) printf "subdir1 wrongly has %s\n" "$m"; bad=1 ;;
 > 	esac
 > done
 > for m in unionfs.ko; do
 > 	case $subdir1strings in
 > 	*"$m"*) ;;
 > 	*) printf "%s is missing from subdir1\n" "$m"; bad=1 ;;
 > 	esac
 > 	case $mainstrings in
 > 	*"$m"*) printf "main wrongly has %s\n" "$m"; bad=1 ;;
 > 	esac
 > done
 > if [ -z "$bad" ]; then
 > 	printf "%s appears to be working correctly\n" "$kldxrefpath"
 > fi
 > 
 > My suggested patch:
 > 
 > Index: usr.sbin/kldxref/kldxref.c
 > ===================================================================
 > --- usr.sbin/kldxref/kldxref.c	(revision 255570)
 > +++ usr.sbin/kldxref/kldxref.c	(working copy)
 > @@ -274,6 +274,16 @@
 >  	exit(1);
 >  }
 >  
 > +int 
 > +compare(const FTSENT* const* a, const FTSENT* const* b)
 > +{
 > +	if ((*a)->fts_info == FTS_D && (*b)->fts_info != FTS_D)
 > +		return 1;
 > +	if ((*a)->fts_info != FTS_D && (*b)->fts_info == FTS_D)
 > +		return -1;
 > +	return strcmp((*a)->fts_name, (*b)->fts_name);
 > +}
 > +
 >  int
 >  main(int argc, char *argv[])
 >  {
 > @@ -315,7 +325,7 @@
 >  		err(1, "%s", argv[0]);
 >  	}
 >  
 > -	ftsp = fts_open(argv, fts_options, 0);
 > +	ftsp = fts_open(argv, fts_options, compare);
 >  	if (ftsp == NULL)
 >  		exit(1);
 >  
 > 
 > -- 
 > Jilles Tjoelker