Improve the interface for dircat_make_node

* dircat.c, dircat.h (dircat_make_node): Use an explicit
  array size for DIRS, fail with ENOMEM is any of them is NULL, and
  release the reference on the non-NULL nodes on any error.
* main.c (root_make_node): Use the new interface.

1 files changed, 9 insertions, 8 deletions

diff --git a/dircat.h b/dircat.h
index cb228526..951d2021 100644
--- a/dircat.h
+++ b/dircat.h
@@ -1,9 +1,10 @@
-/* Append the contents of multiple directories.  DIRS is a
-   NULL-terminated array of directory nodes.  One reference is consumed
-   for each of them, even on ENOMEM, in which case NULL is returned.
-   DIRS has to be static data for now, or at list remain available and
-   unchanged for the duration of the created node's life.  Strange
-   things will happen if they have entries with the same name or if one
-   of them is not a directory.  */
+/* Append the contents of NUM_DIRS directories.  DIRS is an array of
+   directory nodes.  One reference is consumed for each of them. If a
+   memory allocation error occurs, or if one of the directories is a
+   NULL pointer, the references are dropped immediately and NULL is
+   returned.  The given DIRS array is duplicated and can therefore be
+   allocated on the caller's stack.  Strange things will happen if some
+   elements of DIRS have entries with the same name or if one of them is
+   not a directory.  */
 struct node *
-dircat_make_node (struct node **dirs);
+dircat_make_node (struct node *const *dirs, int num_dirs);