From: Valerie Aurora <vaurora@xxxxxxxxxx>
Union mounts design requires that the topmost directory exist for
every single directory at the time lookup completes. This is so that
we don't have to double back and create a whole path's worth of
directories whenever we copy up a file in a directory for the first
time. This greatly simplifies locking and error handling.
Signed-off-by: Valerie Aurora <valerie.aurora@xxxxxxxxx>
---
fs/union.c | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++++
fs/union.h | 3 +++
2 files changed, 56 insertions(+), 0 deletions(-)
diff --git a/fs/union.c b/fs/union.c
index 45552f8..446116f 100644
--- a/fs/union.c
+++ b/fs/union.c
@@ -93,3 +93,56 @@ int union_add_dir(struct path *topmost, struct path *lower,
*path = *lower;
return 0;
}
+
+/**
+ * union_create_topmost_dir - Create a matching dir in the topmost file system
+ *
+ * @parent - parent of target on topmost layer
+ * @name - name of target
+ * @topmost - path of target on topmost layer
+ * @lower - path of source on lower layer
+ *
+ * As we lookup each directory on the lower layer of a union, we
+ * create a matching directory on the topmost layer if it does not
+ * already exist.
+ *
+ * We don't use vfs_mkdir() for a few reasons: don't want to do the
+ * security check, don't want to make the dir opaque, don't need to
+ * sanitize the mode.
+ *
+ * XXX - owner is wrong, set credentials properly
+ * XXX - rmdir() directory on failure of xattr copyup
+ * XXX - not atomic w/ respect to crash
+ */
+
+int union_create_topmost_dir(struct path *parent, struct qstr *name,
+ struct path *topmost, struct path *lower)
+{
+ struct inode *dir = parent->dentry->d_inode;
+ int mode = lower->dentry->d_inode->i_mode;
+ int error;
+
+ BUG_ON(topmost->dentry->d_inode);
+
+ /* XXX - Do we even need to check this? */
+ if (!dir->i_op->mkdir)
+ return -EPERM;
+
+ error = mnt_want_write(parent->mnt);
+ if (error)
+ return error;
+
+ error = dir->i_op->mkdir(dir, topmost->dentry, mode);
+ if (error)
+ goto out;
+
+ error = union_copyup_xattr(lower->dentry, topmost->dentry);
+ if (error)
+ dput(topmost->dentry);
+
+ fsnotify_mkdir(dir, topmost->dentry);
+out:
+ mnt_drop_write(parent->mnt);
+
+ return error;
+}
diff --git a/fs/union.h b/fs/union.h
index bd03d67..1692803 100644
--- a/fs/union.h
+++ b/fs/union.h
@@ -53,6 +53,8 @@ struct union_stack {
extern void d_free_unions(struct dentry *);
extern int union_add_dir(struct path *, struct path *, unsigned int);
+extern int union_create_topmost_dir(struct path *, struct qstr *, struct path *,
+ struct path *);
static inline struct path *union_find_dir(struct dentry *dentry,
unsigned int layer) {
@@ -67,6 +69,7 @@ static inline struct path *union_find_dir(struct dentry *dentry,
#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); })
+#define union_create_topmost_dir(w, x, y, z) ({ BUG(); (0); })
#endif /* CONFIG_UNION_MOUNT */
#endif /* __KERNEL__ */
--
1.7.0.4
--
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