[PATCH 32/74] union-mount: Create union_add_dir()

[Valerie Aurora <valerie.aurora@gmail.com>]

From: Valerie Aurora <vaurora@redhat.com>

union_add_dir() fills out the union stack for the topmost dentry with
the path of the directory in this layer of the union.

Signed-off-by: Valerie Aurora <valerie.aurora@gmail.com>
---
 fs/union.c |   28 ++++++++++++++++++++++++++++
 fs/union.h |    2 ++
 2 files changed, 30 insertions(+), 0 deletions(-)

diff --git a/fs/union.c b/fs/union.c
index a191bef..45552f8 100644
--- a/fs/union.c
+++ b/fs/union.c
@@ -65,3 +65,31 @@ void d_free_unions(struct dentry *topmost)
 	kfree(topmost->d_union_stack);
 	topmost->d_union_stack = NULL;
 }
+
+/**
+ * union_add_dir - Add another layer to a unioned directory
+ *
+ * @topmost - topmost directory
+ * @lower - directory in the current layer
+ * @layer - index of layer to add this at
+ *
+ * @layer counts starting at 0 for the dir below the topmost dir.
+ * Must take a reference to @lower (call path_get()) before calling
+ * this function.
+ */
+
+int union_add_dir(struct path *topmost, struct path *lower,
+		  unsigned int layer)
+{
+	struct path *path;
+	struct dentry *dentry = topmost->dentry;
+	BUG_ON(layer >= dentry->d_sb->s_union_count);
+
+	if (!dentry->d_union_stack)
+		dentry->d_union_stack = union_alloc(topmost);
+	if (!dentry->d_union_stack)
+		return -ENOMEM;
+	path = union_find_dir(dentry, layer);
+	*path = *lower;
+	return 0;
+}
diff --git a/fs/union.h b/fs/union.h
index 353f78d..bd03d67 100644
--- a/fs/union.h
+++ b/fs/union.h
@@ -52,6 +52,7 @@ struct union_stack {
 #define IS_DIR_UNIONED(dentry)	((dentry)->d_union_stack)
 
 extern void d_free_unions(struct dentry *);
+extern int union_add_dir(struct path *, struct path *, unsigned int);
 
 static inline struct path *union_find_dir(struct dentry *dentry,
 					  unsigned int layer) {
@@ -64,6 +65,7 @@ static inline struct path *union_find_dir(struct dentry *dentry,
 #define IS_DIR_UNIONED(x)		(0)
 
 #define d_free_unions(x)		do { } while (0)
+#define union_add_dir(x, y, z)		({ BUG(); (0); })
 #define union_find_dir(x, y)		({ BUG(); (NULL); })
 
 #endif	/* CONFIG_UNION_MOUNT */
-- 
1.7.0.4