Undo separate backing_dev_info for ramdisk.c.

The code was incomplete. Let's re-do it when the other pieces
are in place.

Cset exclude: akpm@osdl.org[torvalds]|ChangeSet|20040521202003|24125

drivers/block/rd.c

@@ -310,26 +310,22 @@ static int rd_ioctl(struct inode *inode, struct file *file,
 }
 
 /*
- * This is the backing_dev_info for the blockdev inode itself.  It doesn't need
- * writeback and it does not contribute to dirty memory accounting.
+ * The backing_dev_info is shared between files which are backed by the ramdisk
+ * inode and by the ramdisk inode itself.  This is a bit unfortunate because
+ * they really want separate semantics.  The files *do* want full writeback
+ * and dirty-memory accounting treatment, whereas the ramdisk blockdev mapping
+ * wants neither.
+ *
+ * So we make things look like a regular blockdev and the cheat in various ways
+ * in the ramdisk inode's a_ops.
  */
+
 static struct backing_dev_info rd_backing_dev_info = {
 	.ra_pages	= 0,	/* No readahead */
 	.memory_backed	= 1,	/* Does not contribute to dirty memory */
 	.unplug_io_fn	= default_unplug_io_fn,
 };
 
-/*
- * This is the backing_dev_info for the files which live atop the ramdisk
- * "device".  These files do need writeback and they do contribute to dirty
- * memory accounting.
- */
-static struct backing_dev_info rd_file_backing_dev_info = {
-	.ra_pages	= 0,	/* No readahead */
-	.memory_backed	= 0,	/* Does contribute to dirty memory */
-	.unplug_io_fn	= default_unplug_io_fn,
-};
-
 static int rd_open(struct inode *inode, struct file *filp)
 {
 	unsigned unit = iminor(inode);
@@ -347,7 +343,6 @@ static int rd_open(struct inode *inode, struct file *filp)
 		mapping = inode->i_mapping;
 		mapping->a_ops = &ramdisk_aops;
 		mapping->backing_dev_info = &rd_backing_dev_info;
-		bdev->bd_inode_backing_dev_info = &rd_file_backing_dev_info;
 
 		/*
 		 * Deep badness.  rd_blkdev_pagecache_IO() needs to allocate