VFS: move dentry_create() from fs/open.c to fs/namei.c

To prepare knfsd's helper dentry_create(), move it to namei.c so that it
can access static functions within.  Callers of dentry_create() can be
viewed as being mostly done with lookup, but still need to perform a few
final checks.  In order to use atomic_open() we want dentry_create() to
be able to access:

	- vfs_prepare_mode
	- may_o_create
	- atomic_open

.. all of which have static declarations.

Signed-off-by: Benjamin Coddington <bcodding@hammerspace.com>
Link: https://patch.msgid.link/42deec53a50e1676e5501f8f1e17967d47b83681.1764259052.git.bcodding@hammerspace.com
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Benjamin Coddington

fs/namei.c

@@ -4937,6 +4937,44 @@ inline struct dentry *start_creating_user_path(
 }
 EXPORT_SYMBOL(start_creating_user_path);
 
+/**
+ * dentry_create - Create and open a file
+ * @path: path to create
+ * @flags: O_ flags
+ * @mode: mode bits for new file
+ * @cred: credentials to use
+ *
+ * Caller must hold the parent directory's lock, and have prepared
+ * a negative dentry, placed in @path->dentry, for the new file.
+ *
+ * Caller sets @path->mnt to the vfsmount of the filesystem where
+ * the new file is to be created. The parent directory and the
+ * negative dentry must reside on the same filesystem instance.
+ *
+ * On success, returns a "struct file *". Otherwise a ERR_PTR
+ * is returned.
+ */
+struct file *dentry_create(const struct path *path, int flags, umode_t mode,
+			   const struct cred *cred)
+{
+	struct file *f;
+	int error;
+
+	f = alloc_empty_file(flags, cred);
+	if (IS_ERR(f))
+		return f;
+
+	error = vfs_create(mnt_idmap(path->mnt), path->dentry, mode, NULL);
+	if (!error)
+		error = vfs_open(path, f);
+
+	if (unlikely(error)) {
+		fput(f);
+		return ERR_PTR(error);
+	}
+	return f;
+}
+EXPORT_SYMBOL(dentry_create);
 
 /**
  * vfs_mknod - create device node or file

fs/open.c

@@ -1141,45 +1141,6 @@ struct file *dentry_open_nonotify(const struct path *path, int flags,
 	return f;
 }
 
-/**
- * dentry_create - Create and open a file
- * @path: path to create
- * @flags: O_ flags
- * @mode: mode bits for new file
- * @cred: credentials to use
- *
- * Caller must hold the parent directory's lock, and have prepared
- * a negative dentry, placed in @path->dentry, for the new file.
- *
- * Caller sets @path->mnt to the vfsmount of the filesystem where
- * the new file is to be created. The parent directory and the
- * negative dentry must reside on the same filesystem instance.
- *
- * On success, returns a "struct file *". Otherwise a ERR_PTR
- * is returned.
- */
-struct file *dentry_create(const struct path *path, int flags, umode_t mode,
-			   const struct cred *cred)
-{
-	struct file *f;
-	int error;
-
-	f = alloc_empty_file(flags, cred);
-	if (IS_ERR(f))
-		return f;
-
-	error = vfs_create(mnt_idmap(path->mnt), path->dentry, mode, NULL);
-	if (!error)
-		error = vfs_open(path, f);
-
-	if (unlikely(error)) {
-		fput(f);
-		return ERR_PTR(error);
-	}
-	return f;
-}
-EXPORT_SYMBOL(dentry_create);
-
 /**
  * kernel_file_open - open a file for kernel internal use
  * @path:	path of the file to open