vfs: add lookup_hash() helper

Overlayfs needs lookup without inode_permission() and already has the name
hash (in form of dentry->d_name on overlayfs dentry).  It also doesn't
support filesystems with d_op->d_hash() so basically it only needs
the actual hashed lookup from lookup_one_len_unlocked()

So add a new helper that does unlocked lookup of a hashed name.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/namei.c b/fs/namei.c
index 3ef87d6..1a1ea79 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2266,6 +2266,33 @@ int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt,
 }
 EXPORT_SYMBOL(vfs_path_lookup);
 
+/**
+ * lookup_hash - lookup single pathname component on already hashed name
+ * @name:      name and hash to lookup
+ * @base:      base directory to lookup from
+ *
+ * The name must have been verified and hashed (see lookup_one_len()).  Using
+ * this after just full_name_hash() is unsafe.
+ *
+ * This function also doesn't check for search permission on base directory.
+ *
+ * Use lookup_one_len_unlocked() instead, unless you really know what you are
+ * doing.
+ *
+ * Do not hold i_mutex; this helper takes i_mutex if necessary.
+ */
+struct dentry *lookup_hash(const struct qstr *name, struct dentry *base)
+{
+       struct dentry *ret;
+
+       ret = lookup_dcache(name, base, 0);
+       if (!ret)
+               ret = lookup_slow(name, base, 0);
+
+       return ret;
+}
+EXPORT_SYMBOL(lookup_hash);
+
 /**
  * lookup_one_len - filesystem helper to lookup single pathname component
  * @name:      pathname component to lookup
@@ -2337,7 +2364,6 @@ struct dentry *lookup_one_len_unlocked(const char *name,
        struct qstr this;
        unsigned int c;
        int err;
-       struct dentry *ret;
 
        this.name = name;
        this.len = len;
@@ -2369,10 +2395,7 @@ struct dentry *lookup_one_len_unlocked(const char *name,
        if (err)
                return ERR_PTR(err);
 
-       ret = lookup_dcache(&this, base, 0);
-       if (!ret)
-               ret = lookup_slow(&this, base, 0);
-       return ret;
+       return lookup_hash(&this, base);
 }
 EXPORT_SYMBOL(lookup_one_len_unlocked);
 

diff --git a/include/linux/namei.h b/include/linux/namei.h
index 77d0170..ec5ec28 100644 (file)
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -79,6 +79,8 @@ extern int kern_path_mountpoint(int, const char *, struct path *, unsigned int);
 
 extern struct dentry *lookup_one_len(const char *, struct dentry *, int);
 extern struct dentry *lookup_one_len_unlocked(const char *, struct dentry *, int);
+struct qstr;
+extern struct dentry *lookup_hash(const struct qstr *, struct dentry *);
 
 extern int follow_down_one(struct path *);
 extern int follow_down(struct path *);