Checklist

What is implemented (maybe these should be in a more sensible order :)

* open regular files and directories:
  * ext2, ext3, ext4
* /dev/null, zero, random, urandom
* epoll fd's
* unix sockets
* ipv4 sockets (except lingering sockets)
* SYSV IPC (message queues, semaphores, and shared memory)
  * except semaphore undo
* Unix98 ptys
* eventfd
* futexes
* process ids
* credentials (userid, group, and POSIX capabilities)
* Smack LSM labels
* pipes
* FIFOs
* signals
* multiple processes, threads
* nested namespaces of:
  * user
  * IPC
  * UTS (hostname)
  * IPC
  * (nested pid namespaces only require userspace support)
* timerfd
* signalfd

What is NOT implemented (please make each a link to a page describing issues, a design for solving, how we will detect it to refuse checkpoint if we will not support it, and "how ugly it will make the kernel")

* mounts
* network devices
* unlinked files
* inotify
* SYSV IPC: semaphore undo
* netlink
* file locks
* file leases
* fowner+sigio
* ptraced tasks
* time namespace