[PATCH v2 1/3] erofs-utils: lib: Add some comments about const-ness around iterate API

[Kelvin Zhang via Linux-erofs <linux-erofs@lists.ozlabs.org>]

The new iterate dir API has non-trivial const correctness requirements.
Document them in comment.

Signed-off-by: Kelvin Zhang <zhangkelvin@google.com>
---
 include/erofs/dir.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/erofs/dir.h b/include/erofs/dir.h
index 77656ca..59bd40d 100644
--- a/include/erofs/dir.h
+++ b/include/erofs/dir.h
@@ -39,6 +39,14 @@ typedef int (*erofs_readdir_cb)(struct erofs_dir_context *);
  * the callback context. |de_namelen| is the exact dirent name length.
  */
 struct erofs_dir_context {
+	/* During execution of |erofs_iterate_dir|, the function needs
+	 * to read the values inside |erofs_inode* dir|. So it is important
+	 * that the callback function does not modify stuct pointed by
+	 * |dir|. It is OK to repoint |dir| to other objects.
+	 * Unfortunately, it's not possible to enforce this restriction
+	 * with const keyword, as |erofs_iterate_dir| needs to modify
+	 * struct pointed by |dir|.
+	 */
 	struct erofs_inode *dir;
 	erofs_readdir_cb cb;
 	erofs_nid_t pnid;		/* optional */
-- 
2.34.1.448.ga2b2bfdf31-goog