vfs: Provide a mount_pseudo-replacement for the new mount API

Provide a function, init_pseudo(), that provides a common
infrastructure for converting pseudo-filesystems that can never be
mountable.

[AV: once all users of mount_pseudo_xattr() get converted, it will be folded
into pseudo_fs_get_tree()]

Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-fsdevel@vger.kernel.org

include/linux/pseudo_fs.h

@@ -0,0 +1,16 @@
+#ifndef __LINUX_PSEUDO_FS__
+#define __LINUX_PSEUDO_FS__
+
+#include <linux/fs_context.h>
+
+struct pseudo_fs_context {
+	const struct super_operations *ops;
+	const struct xattr_handler **xattr;
+	const struct dentry_operations *dops;
+	unsigned long magic;
+};
+
+struct pseudo_fs_context *init_pseudo(struct fs_context *fc,
+				      unsigned long magic);
+
+#endif