[PATCH 2/5] initmpfs v2: Move bdi setup from init_rootfs to init_ramfs

[Rob Landley <rob@landley.net>]

From: Rob Landley <rob@landley.net>

Even though ramfs hasn't got a backing device, commit e0bf68ddec4f added one
anyway, and put the initialization in init_rootfs() since that's the first
user, leaving it out of init_ramfs() to avoid duplication.

But initmpfs uses init_tmpfs() instead, so move the init into the filesystem's
init function, add a "once" guard to prevent duplicate initialization, and
call the filesystem init from rootfs init.

This goes part of the way to allowing ramfs to be built as a module.

Signed-off-by: Rob Landley <rob@landley.net>
---

 fs/ramfs/inode.c |   23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

--- initold/fs/ramfs/inode.c	2013-06-28 15:12:03.205879730 -0500
+++ initold2/fs/ramfs/inode.c	2013-06-28 15:12:12.425880115 -0500
@@ -275,21 +275,34 @@
 
 static int __init init_ramfs_fs(void)
 {
-	return register_filesystem(&ramfs_fs_type);
+	static unsigned long once;
+	int err;
+
+	if (test_and_set_bit(1, &once))
+		return 0;
+
+	err = bdi_init(&ramfs_backing_dev_info);
+	if (err)
+		return err;
+
+	err = register_filesystem(&ramfs_fs_type);
+	if (err)
+		bdi_destroy(&ramfs_backing_dev_info);
+
+	return err;
 }
 module_init(init_ramfs_fs)
 
 int __init init_rootfs(void)
 {
-	int err;
+	int err = register_filesystem(&rootfs_fs_type);
 
-	err = bdi_init(&ramfs_backing_dev_info);
 	if (err)
 		return err;
 
-	err = register_filesystem(&rootfs_fs_type);
+	err = init_ramfs_fs();
 	if (err)
-		bdi_destroy(&ramfs_backing_dev_info);
+		unregister_filesystem(&rootfs_fs_type);
 
 	return err;
 }