expr: Document error handling for expr_annotate().

Signed-off-by: Justin Pettit <jpettit@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>

diff --git a/ovn/lib/expr.c b/ovn/lib/expr.c
index 8270b82..8ec62b5 100644 (file)
--- a/ovn/lib/expr.c
+++ b/ovn/lib/expr.c
@@ -1480,7 +1480,10 @@ expr_annotate__(struct expr *expr, const struct shash *symtab,
  *     - Expands references to predicate symbols, by replacing them by the
  *       expressions that they expand to.
  *
- * In each case, annotation occurs recursively as necessary. */
+ * In each case, annotation occurs recursively as necessary.
+ *
+ * On failure, returns NULL and sets '*errorp' to an explanatory error
+ * message, which the caller must free. */
 struct expr *
 expr_annotate(struct expr *expr, const struct shash *symtab, char **errorp)
 {