[Toybox] What does the du.c patch do?

[Rob Landley]

Going through Ashwini's patch stack from last month. (Sorry for the delay,
but I think I applied all the trivial ones in earlier passes.)

What does the du.c patch do?

  $ mkdir sub
  $ ln -s . sub/here
  $ ln -s loop sub/loop
  $ ./toybox du sub
  4     sub

There's also a hardlink filter (disabled via -l)...

I'm tempted to add the following to lib/dirtree.c

+// Have we already seen this node?
+int dirtree_seen(struct dirtree *try, struct stat *st)
+{
+  while (try) {
+    if (try->st.st_ino==st->st_ino && try->st.st_dev==st->st_dev) return 1;
+    try = try->parent;
+  }
+
+  return 0;
+}
+

But the existing user I can think of that's already doing this is in cp.c:

    // Detect recursive copies via repeated top node (cp -R .. .) or
    // identical source/target (fun with hardlinks).
    if ((TT.top.st_dev == try->st.st_dev && TT.top.st_ino == try->st.st_ino
         && (catch = TT.destname))
        || (!fstatat(cfd, catch, &cst, 0) && cst.st_dev == try->st.st_dev
         && cst.st_ino == try->st.st_ino))
    {
      error_msg("'%s' is '%s'", catch, err = dirtree_path(try, 0));
      free(err);

      return 0;
    }

Which seems to work?

Anyway, could you give me a testcase where the du.c patch you submitted makes a
difference?

Rob