[GSoC] Make vkernels checkpointable

Hello!

This summer I will be working on making it possible to generate a
checkpoint file of a vkernel and restore it later in such way it won't
be noticeable for its virtual processes. Since DragonFly already has
support for checkpointing common, "normal" processes I am going to,
basically, just extend its abilities to fit the vkernels' specific
needs. Moreover, there already has been an attempt [1] to make
vkernels checkpointable and I am going to take advantage of the work
that was done.

Firstly, I will complete support for checkpointing processes with
multiple threads what is a feature not only vkernels will take benefit
from. Then, I am going to implement restoring network interfaces (and
their configuration) as well as console mode after vkernel is resumed.

During the second half of the Google Summer of Code period I am going
to implement support for kqueue based IO as well as MAP_VPAGETABLE and
vmspaces which are essential for vkernels proper functioning.

My proposal is available here [2]. You can track my progress in my
github repository, branch vkernel_chkpt [3].

Paweł Dziepak

[1] https://github.com/iriina/DragonFlyBSD/commits/test2.10.1
[2] http://www.google-melange.com/gsoc/proposal/review/google/gsoc2013/pdziepak/17001
[3] https://github.com/pdziepak/DragonFlyBSD/tree/vkernel_chkpt