[PATCH v2 2/4] d_walk: add leave callback

[Ondrej Mosnacek <omosnace@redhat.com>]

Add an optional callback that gets called when d_walk is *leaving* a
dentry. This will be used in a later patch to provide a function to
safely perform d_genocide on live trees.

Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
---
 fs/dcache.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 9ed4c0f99e57..70afcb6e6892 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1260,13 +1260,15 @@ enum d_walk_ret {
  * d_walk - walk the dentry tree
  * @parent:	start of walk
  * @lock_inode	whether to lock also parent inode
- * @data:	data passed to @enter() and @finish()
+ * @data:	data passed to @enter() and @leave()
  * @enter:	callback when first entering the dentry
+ * @leave:	callback when leaving the dentry
  *
  * The @enter() callbacks are called with d_lock held.
  */
 static void d_walk(struct dentry *parent, bool lock_inode, void *data,
-		   enum d_walk_ret (*enter)(void *, struct dentry *))
+		   enum d_walk_ret (*enter)(void *, struct dentry *),
+		   void (*leave)(void *, struct dentry *))
 {
 	struct dentry *this_parent;
 	struct list_head *next;
@@ -1339,6 +1341,8 @@ resume:
 			}
 			goto repeat;
 		}
+		if (leave)
+			leave(data, dentry);
 		spin_unlock(&dentry->d_lock);
 	}
 	/*
@@ -1350,6 +1354,8 @@ ascend:
 		struct dentry *child = this_parent;
 		this_parent = child->d_parent;
 
+		if (leave)
+			leave(data, child);
 		spin_unlock(&child->d_lock);
 		if (lock_inode) {
 			inode_unlock(child->d_inode);
@@ -1370,6 +1376,8 @@ ascend:
 		rcu_read_unlock();
 		goto resume;
 	}
+	if (leave)
+		leave(data, parent);
 	if (need_seqretry(&rename_lock, seq))
 		goto rename_retry;
 	rcu_read_unlock();
@@ -1425,7 +1433,7 @@ int path_has_submounts(const struct path *parent)
 	struct check_mount data = { .mnt = parent->mnt, .mounted = 0 };
 
 	read_seqlock_excl(&mount_lock);
-	d_walk(parent->dentry, false, &data, path_check_mount);
+	d_walk(parent->dentry, false, &data, path_check_mount, NULL);
 	read_sequnlock_excl(&mount_lock);
 
 	return data.mounted;
@@ -1564,7 +1572,7 @@ void shrink_dcache_parent(struct dentry *parent)
 		struct select_data data = {.start = parent};
 
 		INIT_LIST_HEAD(&data.dispose);
-		d_walk(parent, false, &data, select_collect);
+		d_walk(parent, false, &data, select_collect, NULL);
 
 		if (!list_empty(&data.dispose)) {
 			shrink_dentry_list(&data.dispose);
@@ -1575,7 +1583,7 @@ void shrink_dcache_parent(struct dentry *parent)
 		if (!data.found)
 			break;
 		data.victim = NULL;
-		d_walk(parent, false, &data, select_collect2);
+		d_walk(parent, false, &data, select_collect2, NULL);
 		if (data.victim) {
 			struct dentry *parent;
 			spin_lock(&data.victim->d_lock);
@@ -1622,7 +1630,7 @@ static enum d_walk_ret umount_check(void *_data, struct dentry *dentry)
 static void do_one_tree(struct dentry *dentry)
 {
 	shrink_dcache_parent(dentry);
-	d_walk(dentry, false, dentry, umount_check);
+	d_walk(dentry, false, dentry, umount_check, NULL);
 	d_drop(dentry);
 	dput(dentry);
 }
@@ -1679,7 +1687,7 @@ void d_invalidate(struct dentry *dentry)
 	shrink_dcache_parent(dentry);
 	for (;;) {
 		struct dentry *victim = NULL;
-		d_walk(dentry, false, &victim, find_submount);
+		d_walk(dentry, false, &victim, find_submount, NULL);
 		if (!victim) {
 			if (had_submounts)
 				shrink_dcache_parent(dentry);
@@ -3129,7 +3137,7 @@ static enum d_walk_ret d_genocide_kill(void *data, struct dentry *dentry)
 
 void d_genocide(struct dentry *parent)
 {
-	d_walk(parent, false, parent, d_genocide_kill);
+	d_walk(parent, false, parent, d_genocide_kill, NULL);
 }
 
 EXPORT_SYMBOL(d_genocide);
-- 
2.21.0