linux-kernel - [PATCH 30/73] union-mount: Create needs_lookup

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Date:	Tue, 21 Feb 2012 18:01:18 +0000
From:	David Howells <dhowells@...hat.com>
To:	linux-fsdevel@...r.kernel.org, viro@...IV.linux.org.uk,
	valerie.aurora@...il.com
Cc:	linux-kernel@...r.kernel.org, David Howells <dhowells@...hat.com>
Subject: [PATCH 30/73] union-mount: Create needs_lookup_union() [ver #2]

From: Valerie Aurora <vaurora@...hat.com>

needs_lookup_union() tests if a path could possibly require a union
lookup.

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

 fs/union.h             |   25 +++++++++++++++++++++++++
 include/linux/dcache.h |    2 ++
 2 files changed, 27 insertions(+), 0 deletions(-)

diff --git a/fs/union.h b/fs/union.h
index 990dd16..757f28c 100644
--- a/fs/union.h
+++ b/fs/union.h
@@ -73,6 +73,26 @@ struct path *union_find_dir(struct dentry *dentry, unsigned int layer)
 	return &dentry->d_union_stack->u_dirs[layer];
 }
 
+/*
+ * Determine whether we need to perform unionmount traversal or the copyup of a
+ * dentry.
+ */
+static inline
+bool needs_lookup_union(struct path *parent_path, struct path *path)
+{
+	if (!IS_DIR_UNIONED(parent_path->dentry))
+		return false;
+
+	/* Either already built or crossed a mountpoint to not-unioned mnt */
+	/* XXX are bind mounts root? think not */
+	if (IS_ROOT(path->dentry))
+		return false;
+
+	/* It's okay not to have the lock; will recheck in lookup_union() */
+	/* XXX set for root dentry at mount? */
+	return !(path->dentry->d_flags & DCACHE_UNION_LOOKUP_DONE);
+}
+
 #else /* CONFIG_UNION_MOUNT */
 
 static inline
@@ -100,4 +120,9 @@ static inline int union_create_topmost_dir(struct path *parent, struct qstr *nam
 	return 0;
 }
 
+static inline bool needs_lookup_union(struct path *parent_path, struct path *path)
+{
+	return false;
+}
+
 #endif	/* CONFIG_UNION_MOUNT */
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index e2d44e1..79833ae 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -245,6 +245,8 @@ struct dentry_operations {
 #define DCACHE_MANAGED_DENTRY \
 	(DCACHE_MOUNTED|DCACHE_NEED_AUTOMOUNT|DCACHE_MANAGE_TRANSIT)
 
+#define DCACHE_UNION_LOOKUP_DONE 0x100000 /* Union lookup was called on this dentry */
+
 extern seqlock_t rename_lock;
 
 static inline int dname_external(struct dentry *dentry)

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