How to start the extra-credit...
- Make a block/drive api
- Make a simple shell
- diskinfo
- exit
- mkdir / rmdir
- ls
- cd
- mv
- touch (create a file)
- cp
- chmod
- chown
- cat
- ed

-----------------------------------

Hypervisors - Type 1 (Machine > Hypervisor > Guest(s))

VM - Efficient, Accurate, and Secure

Why Accurate?
- Valid testing
- Acts like a real computer cheaply
- Real Un-modified OSes

How would an OS be different if it "knew" it was in a VM?
- Cooperate with the VM (hypervisor)
- Explicit APIs for sharing between Host and Guest (Type 2)
- Implicit: Turn off block cache!
-- Real machine has 16 GB
-- OS (in VM) wants to use ALL of memory (8 GB)
-- It does e.g. block cache (even though real 2GB)
-- This causes unnecessary virtual page usage/contention.
- Implicit: Support only one hard-drive driver.
-- Simplifies the OS and perf.
- Explicit: What kind of hard-drive does a VM support?
-- API for making it bigger (i.e. more features)
- Explicit: Tell the host what you are doing
-- VM wants to know the REAL memory that isn't in cache
-- Linux could tell Xen ... "I will need this page soon"
-- API for telling the VMM what's happening
- Explicit: Inter-VM communication API
-- 3 VMs and they communicate
-- On a fake network (Ethernet hub)
-- Efficiency of SHM vs Writing/Reading to Files

Take all the APIs of the Hypervisor..
- Para-virtualization
.... it's not a VMM, it's just an OS
- It's a kind of MICROKERNEL
.....
- Microkernels that WON!

Unikernel / Exokernel
- Why is my VM running multiple tty?
- Take away everything from an OS that you don't need
- Ring-0 only OSes
- Unified address space
- For a DB... remove the filesystem
- For a compute server... remove all persistent storage
- Q: How expensive to make?
-- Surprisingly easy
- Q: How much do we save?

Tour of Unikernels
- IncludeOS
- BareMetal