From: Valerie Aurora <vaurora@xxxxxxxxxx>
struct union_stack records the stack of directories unioned at this
directory. A union_stack is an array of struct paths, dynamically
allocated when the dentry for the topmost directory is created. The
topmost dentry contains a pointer to the union_stack.
Signed-off-by: Valerie Aurora <valerie.aurora@xxxxxxxxx>
---
fs/dcache.c | 3 ++
fs/union.h | 54 ++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/dcache.h | 22 +++++++++++++++++-
3 files changed, 77 insertions(+), 2 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index ff3f949..566acf7 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -961,6 +961,9 @@ struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
INIT_LIST_HEAD(&dentry->d_lru);
INIT_LIST_HEAD(&dentry->d_subdirs);
INIT_LIST_HEAD(&dentry->d_alias);
+#ifdef CONFIG_UNION_MOUNT
+ dentry->d_union_stack = NULL;
+#endif
if (parent) {
dentry->d_parent = dget(parent);
diff --git a/fs/union.h b/fs/union.h
new file mode 100644
index 0000000..38b26fd
--- /dev/null
+++ b/fs/union.h
@@ -0,0 +1,54 @@
+ /*
+ * VFS-based union mounts for Linux
+ *
+ * Copyright (C) 2004-2007 IBM Corporation, IBM Deutschland Entwicklung GmbH.
+ * Copyright (C) 2007-2009 Novell Inc.
+ * Copyright (C) 2009-2010 Red Hat, Inc.
+ *
+ * Author(s): Jan Blunck (j.blunck@xxxxxxxxxxxxx)
+ * Valerie Aurora <vaurora@xxxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; version 2
+ * of the License.
+ */
+#ifndef __LINUX_UNION_H
+#define __LINUX_UNION_H
+#ifdef __KERNEL__
+
+#ifdef CONFIG_UNION_MOUNT
+
+/*
+ * WARNING! Confusing terminology alert.
+ *
+ * Note that the directions "up" and "down" in union mounts are the
+ * opposite of "up" and "down" in normal VFS operation terminology.
+ * "up" in the rest of the VFS means "towards the root of the mount
+ * tree." If you mount B on top of A, following B "up" will get you
+ * A. In union mounts, "up" means "towards the most recently mounted
+ * layer of the union stack." If you union mount B on top of A,
+ * following A "up" will get you to B. Another way to put it is that
+ * "up" in the VFS means going from this mount towards the direction
+ * of its mnt->mnt_parent pointer, but "up" in union mounts means
+ * going in the opposite direction (until you run out of union
+ * layers).
+ */
+
+/*
+ * The union_stack structure. It is an array of struct paths of
+ * directories below the topmost directory in a unioned directory, The
+ * topmost dentry has a pointer to this structure. The topmost dentry
+ * can only be part of one union, so we can reference it from the
+ * dentry, but lower dentries can be part of multiple union stacks.
+ *
+ * The number of dirs actually allocated is kept in the superblock,
+ * s_union_count.
+ */
+struct union_stack {
+ struct path u_dirs[0];
+};
+
+#endif /* CONFIG_UNION_MOUNT */
+#endif /* __KERNEL__ */
+#endif /* __LINUX_UNION_H */
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 19ddb8c..ddf3d2d 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -79,12 +79,28 @@ full_name_hash(const unsigned char *name, unsigned int len)
* Try to keep struct dentry aligned on 64 byte cachelines (this will
* give reasonable cacheline footprint with larger lines without the
* large memory footprint increase).
+ *
+ * XXX DNAME_INLINE_LEN_MIN is kind of pitiful on 64bit + union
+ * mounts. May be worth tuning up, but either we go to 256 bytes and
+ * a wasteful 88 bytes of d_iname, or we lose 64-byte aligment.
*/
#ifdef CONFIG_64BIT
+
+#ifdef CONFIG_UNION_MOUNT
+#define DNAME_INLINE_LEN_MIN 24 /* 192 bytes */
+#else
#define DNAME_INLINE_LEN_MIN 32 /* 192 bytes */
+#endif /* CONFIG_UNION_MOUNT */
+
+#else
+
+#ifdef CONFIG_UNION_MOUNT
+#define DNAME_INLINE_LEN_MIN 36 /* 128 bytes */
#else
#define DNAME_INLINE_LEN_MIN 40 /* 128 bytes */
-#endif
+#endif /* CONFIG_UNION_MOUNT */
+
+#endif /* CONFIG_64BIT */
struct dentry {
atomic_t d_count;
@@ -100,7 +116,9 @@ struct dentry {
struct hlist_node d_hash; /* lookup hash list */
struct dentry *d_parent; /* parent directory */
struct qstr d_name;
-
+#ifdef CONFIG_UNION_MOUNT
+ struct union_stack *d_union_stack; /* dirs in union stack */
+#endif
struct list_head d_lru; /* LRU list */
/*
* d_child and d_rcu can share memory
--
1.7.0.4
--
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