fs: name case update method

smpfs and ncpfs want to update a live dentry name in-place. Rather than
have them open code the locking, provide a documented dcache API.
Signed-off-by: Nick Piggin <npiggin@kernel.dk>

drivers/staging/smbfs/cache.c

@@ -145,8 +145,8 @@ smb_fill_cache(struct file *filp, void *dirent, filldir_t filldir,
 			goto end_advance;
 	} else {
 		hashed = 1;
-		memcpy((char *) newdent->d_name.name, qname->name,
-		       newdent->d_name.len);
+		/* dir i_mutex is locked because we're in readdir */
+		dentry_update_name_case(newdent, qname);
 	}
 
 	if (!newdent->d_inode) {

fs/dcache.c

@@ -1589,6 +1589,33 @@ void d_rehash(struct dentry * entry)
 }
 EXPORT_SYMBOL(d_rehash);
 
+/**
+ * dentry_update_name_case - update case insensitive dentry with a new name
+ * @dentry: dentry to be updated
+ * @name: new name
+ *
+ * Update a case insensitive dentry with new case of name.
+ *
+ * dentry must have been returned by d_lookup with name @name. Old and new
+ * name lengths must match (ie. no d_compare which allows mismatched name
+ * lengths).
+ *
+ * Parent inode i_mutex must be held over d_lookup and into this call (to
+ * keep renames and concurrent inserts, and readdir(2) away).
+ */
+void dentry_update_name_case(struct dentry *dentry, struct qstr *name)
+{
+	BUG_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
+	BUG_ON(dentry->d_name.len != name->len); /* d_lookup gives this */
+
+	spin_lock(&dcache_lock);
+	spin_lock(&dentry->d_lock);
+	memcpy((unsigned char *)dentry->d_name.name, name->name, name->len);
+	spin_unlock(&dentry->d_lock);
+	spin_unlock(&dcache_lock);
+}
+EXPORT_SYMBOL(dentry_update_name_case);
+
 /*
  * When switching names, the actual string doesn't strictly have to
  * be preserved in the target - because we're dropping the target

fs/ncpfs/dir.c

@@ -611,35 +611,12 @@ ncp_fill_cache(struct file *filp, void *dirent, filldir_t filldir,
 			shrink_dcache_parent(newdent);
 
 		/*
-		 * It is not as dangerous as it looks.  NetWare's OS2 namespace is
-		 * case preserving yet case insensitive.  So we update dentry's name
-		 * as received from server.  We found dentry via d_lookup with our
-		 * hash, so we know that hash does not change, and so replacing name
-		 * should be reasonably safe.
+		 * NetWare's OS2 namespace is case preserving yet case
+		 * insensitive.  So we update dentry's name as received from
+		 * server. Parent dir's i_mutex is locked because we're in
+		 * readdir.
 		 */
-		if (qname.len == newdent->d_name.len &&
-		    memcmp(newdent->d_name.name, qname.name, newdent->d_name.len)) {
-			struct inode *inode = newdent->d_inode;
-
-			/*
-			 * Inside ncpfs all uses of d_name are either for debugging,
-			 * or on functions which acquire inode mutex (mknod, creat,
-			 * lookup).  So grab i_mutex here, to be sure.  d_path
-			 * uses dcache_lock when generating path, so we should too.
-			 * And finally d_compare is protected by dentry's d_lock, so
-			 * here we go.
-			 */
-			if (inode)
-				mutex_lock(&inode->i_mutex);
-			spin_lock(&dcache_lock);
-			spin_lock(&newdent->d_lock);
-			memcpy((char *) newdent->d_name.name, qname.name,
-								newdent->d_name.len);
-			spin_unlock(&newdent->d_lock);
-			spin_unlock(&dcache_lock);
-			if (inode)
-				mutex_unlock(&inode->i_mutex);
-		}
+		dentry_update_name_case(newdent, &qname);
 	}
 
 	if (!newdent->d_inode) {
@@ -657,7 +634,7 @@ ncp_fill_cache(struct file *filp, void *dirent, filldir_t filldir,
 	} else {
 		struct inode *inode = newdent->d_inode;
 
-		mutex_lock(&inode->i_mutex);
+		mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
 		ncp_update_inode2(inode, entry);
 		mutex_unlock(&inode->i_mutex);
 	}

include/linux/dcache.h

@@ -290,6 +290,8 @@ static inline struct dentry *d_add_unique(struct dentry *entry, struct inode *in
 	return res;
 }
 
+extern void dentry_update_name_case(struct dentry *, struct qstr *);
+
 /* used for rename() and baskets */
 extern void d_move(struct dentry *, struct dentry *);
 extern struct dentry *d_ancestor(struct dentry *, struct dentry *);