From: viro@parcelfarce.linux.theplanet.co.uk

* drivers/block/initrd.c gone

* chunk of memory where the current tree would look for intird image is
  checked for being a valid initramfs image first; then, it is either
  unpacked (in addition to normal built-in image) or, if it wasn't a valid
  image, copied into a regular file on rootfs called /dev/initrd.  Then
  memory is freed.

Result:

a) we can put initramfs image in place of initrd one and kernel will DTRT.

b) initrd images still work as usual; code that shoves the thing to
   ramdisk, etc.  doesn't care whether it reads from a block device or
   regular file.

c) initrd.c is gone, so is fake block device and a lot of irregularities
   with it.

It has been in -mm for almost two weeks with no reported problems.