+
+static bool
+same_fd (int fd1, int fd2)
+{
+ struct stat sb1, sb2;
+ return (fstat (fd1, &sb1) == 0
+ && fstat (fd2, &sb2) == 0
+ && SAME_INODE (sb1, sb2));
+}
+
+static void
+fd_ring_print (FTS const *sp, FILE *stream, char const *msg)
+{
+ I_ring const *fd_ring = &sp->fts_fd_ring;
+ unsigned int i = fd_ring->fts_front;
+ char *cwd = getcwdat (sp->fts_cwd_fd, NULL, 0);
+ fprintf (stream, "=== %s ========== %s\n", msg, cwd);
+ free (cwd);
+ if (i_ring_empty (fd_ring))
+ return;
+
+ while (true)
+ {
+ int fd = fd_ring->fts_fd_ring[i];
+ if (fd < 0)
+ fprintf (stream, "%d: %d:\n", i, fd);
+ else
+ {
+ char *wd = getcwdat (fd, NULL, 0);
+ fprintf (stream, "%d: %d: %s\n", i, fd, wd);
+ free (wd);
+ }
+ if (i == fd_ring->fts_back)
+ break;
+ i = (i + I_RING_SIZE - 1) % I_RING_SIZE;
+ }
+}
+
+/* Ensure that each file descriptor on the fd_ring matches a
+ parent, grandparent, etc. of the current working directory. */
+static void
+fd_ring_check (FTS const *sp)
+{
+ if (!fts_debug)
+ return;
+
+ /* Make a writable copy. */
+ I_ring fd_w = sp->fts_fd_ring;
+
+ int cwd_fd = sp->fts_cwd_fd;
+ cwd_fd = dup (cwd_fd);
+ char *dot = getcwdat (cwd_fd, NULL, 0);
+ error (0, 0, "===== check ===== cwd: %s", dot);
+ free (dot);
+ while ( ! i_ring_empty (&fd_w))
+ {
+ int fd = i_ring_pop (&fd_w);
+ if (0 <= fd)
+ {
+ int parent_fd = openat (cwd_fd, "..", O_RDONLY);
+ if (parent_fd < 0)
+ {
+ // Warn?
+ break;
+ }
+ if (!same_fd (fd, parent_fd))
+ {
+ char *cwd = getcwdat (fd, NULL, 0);
+ error (0, errno, "ring : %s", cwd);
+ char *c2 = getcwdat (parent_fd, NULL, 0);
+ error (0, errno, "parent: %s", c2);
+ free (cwd);
+ free (c2);
+ fts_assert (0);
+ }
+ close (cwd_fd);
+ cwd_fd = parent_fd;
+ }
+ }
+ close (cwd_fd);
+}