[PATCH 27/73] union-mount: Create union_add_dir() [ver #2]

[David Howells]

From: Valerie Aurora <vaurora@xxxxxxxxxx>

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

Original-author: Valerie Aurora <vaurora@xxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---

 fs/union.c |   28 ++++++++++++++++++++++++++++
 fs/union.h |    8 ++++++++
 2 files changed, 36 insertions(+), 0 deletions(-)

diff --git a/fs/union.c b/fs/union.c
index 77d6a74..1e459b0 100644
--- a/fs/union.c
+++ b/fs/union.c
@@ -60,3 +60,31 @@ 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.
+ *
+ * This transfers the caller's references to the constituents of *lower to the
+ * union stack.
+ */
+int union_add_dir(struct path *topmost, struct path *lower, unsigned layer)
+{
+	struct dentry *dentry = topmost->dentry;
+	struct path *path;
+
+	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 04a02ec..f39c88d 100644
--- a/fs/union.h
+++ b/fs/union.h
@@ -57,6 +57,7 @@ static inline bool IS_DIR_UNIONED(struct dentry *dentry)
 }
 
 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)
@@ -77,4 +78,11 @@ struct path *union_find_dir(struct dentry *dentry, unsigned int layer)
 static inline bool IS_DIR_UNIONED(struct dentry *dentry) { return false; }
 static inline void d_free_unions(struct dentry *dentry) {}
 
+static inline
+int union_add_dir(struct path *topmost, struct path *lower, unsigned layer)
+{
+	BUG();
+	return 0;
+}
+
 #endif	/* CONFIG_UNION_MOUNT */

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