relay buffer-only channels (resubmit)

Hello,

This is a resubmit of the buffer-only channels implementation for relay. Basically I followed Pekka Enberg's suggestion of doing things CPU-hotplug-aware.

The first two patches allow relay to set up an early initcall for registering a CPU hotplug notifier. This has to run before SMP is up, so non-boot CPUs get a buffer as soon as they're up.

Feel free to ask any questions or suggest anything.

Eduard - Gabriel Munteanu (3):
Unignore vmlinux.lds.h from Git.
Better interface for hooking early initcalls.
relay: Add buffer-only channels; useful for early logging.

 .gitignore                          |    1 +
 Documentation/filesystems/relay.txt |   11 +++
 include/asm-generic/vmlinux.lds.h   |    2 +
 include/linux/init.h                |    7 ++
 include/linux/relay.h               |    5 +
 init/main.c                         |   13 +++-
 kernel/relay.c                      |  141 +++++++++++++++++++++++++++--------
 7 files changed, 147 insertions(+), 33 deletions(-)