Add reference counting for devfs paths containing user created symbolic

links. The reference counting is needed to be able to determine if a
specific devfs path exists. For true device file paths we can traverse
the cdevp_list but a separate directory list is needed for user created
symbolic links.

Add a new directory entry flag DE_USER to mark entries which should
unreference their parent directory on deletion.

A new function to traverse cdevp_list and the directory list will be
introduced in a separate commit.

Idea from:	kib
Reviewed by:	kib

1 files changed, 12 insertions, 1 deletions

diff --git a/sys/fs/devfs/devfs_devs.c b/sys/fs/devfs/devfs_devs.c
index 60c296b..99b33ec 100644
--- a/sys/fs/devfs/devfs_devs.c
+++ b/sys/fs/devfs/devfs_devs.c
@@ -338,6 +338,10 @@ devfs_delete(struct devfs_mount *dm, struct devfs_dirent *de, int flags)
 		dd = devfs_parent_dirent(de);
 		if (dd != NULL)
 			DEVFS_DE_HOLD(dd);
+		if (de->de_flags & DE_USER) {
+			KASSERT(dd != NULL, ("devfs_delete: NULL dd"));
+			devfs_dir_unref_de(dm, dd);
+		}
 	} else
 		dd = NULL;
 
@@ -396,10 +400,17 @@ devfs_purge(struct devfs_mount *dm, struct devfs_dirent *dd)
 
 	DEVFS_DE_HOLD(dd);
 	for (;;) {
-		de = TAILQ_FIRST(&dd->de_dlist);
+		/*
+		 * Use TAILQ_LAST() to remove "." and ".." last.
+		 * We might need ".." to resolve a path in
+		 * devfs_dir_unref_de().
+		 */
+		de = TAILQ_LAST(&dd->de_dlist, devfs_dlist_head);
 		if (de == NULL)
 			break;
 		TAILQ_REMOVE(&dd->de_dlist, de, de_list);
+		if (de->de_flags & DE_USER)
+			devfs_dir_unref_de(dm, dd);
 		if (de->de_flags & (DE_DOT | DE_DOTDOT))
 			devfs_delete(dm, de, DEVFS_DEL_NORECURSE);
 		else if (de->de_dirent->d_type == DT_DIR)