needs_lookup_union() tests if a path could possibly require a union
lookup.
Signed-off-by: Valerie Aurora <vaurora@xxxxxxxxxx>
---
fs/union.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
fs/union.h | 2 ++
2 files changed, 51 insertions(+), 0 deletions(-)
diff --git a/fs/union.c b/fs/union.c
index bc53066..a9427bf 100644
--- a/fs/union.c
+++ b/fs/union.c
@@ -127,3 +127,52 @@ int union_create_topmost_dir(struct path *parent, struct qstr *name,
return res;
}
+
+/**
+ * needs_lookup_union - Avoid union lookup when not necessary
+ *
+ * @parent_path: path of the parent directory
+ * @path: path of the lookup target
+ *
+ * Check to see if the target needs union lookup - that is, needs its
+ * union stack constructed. Two cases need union lookup in a unioned
+ * parent directory: the target is a directory without a union stack,
+ * or the target is a negative dentry.
+ *
+ * Returns 0 if this dentry does not need union lookup. Returns 1 if
+ * it is possible this dentry needs union lookup.
+ */
+
+int needs_lookup_union(struct path *parent_path, struct path *path)
+{
+ if (!IS_DIR_UNIONED(parent_path->dentry))
+ return 0;
+
+ /* Root dir union stack created at mount (if this is a unioned mnt) */
+ if (IS_ROOT(path->dentry))
+ return 0;
+
+ /* Union stack for target already created, clearly */
+ if (IS_DIR_UNIONED(path->dentry))
+ return 0;
+
+ if (d_is_whiteout(path->dentry))
+ return 0;
+
+ if (IS_OPAQUE(parent_path->dentry->d_inode) &&
+ !d_is_fallthru(path->dentry))
+ return 0;
+
+ /* Non-directories don't need union stacks */
+ if (path->dentry->d_inode &&
+ !S_ISDIR(path->dentry->d_inode->i_mode))
+ return 0;
+
+ /*
+ * XXX Things with nothing below them in a union dir
+ * (including negative dentries) must always go through union
+ * lookup. This is like negative dentries in the dcache.
+ * Write some optimization for this case.
+ */
+ return 1;
+}
diff --git a/fs/union.h b/fs/union.h
index c496823..0c8fbca 100644
--- a/fs/union.h
+++ b/fs/union.h
@@ -56,6 +56,7 @@ 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 *);
+extern int needs_lookup_union(struct path *, struct path *);
static inline struct path *union_find_dir(struct dentry *dentry,
unsigned int layer) {
@@ -72,6 +73,7 @@ static inline struct path *union_find_dir(struct dentry *dentry,
#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); })
+#define needs_lookup_union(x, y) ({ (0); })
#endif /* CONFIG_UNION_MOUNT */
#endif /* __KERNEL__ */
--
1.6.3.3
--
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