S4 hibernate support for FreeBSD

Hi all!

The FreeBSD Foundation is beginning work on adding S4 (hibernate) support to
FreeBSD. Currently we have S4BIOS support, but no hibernate support on modern
platforms.

We have started exploring what would be required to bring S4 to FreeBSD and
kib@ has written up some initial findings, along with some open design
questions. We'd like to share this early document with the community to gather
feedback or identify any pitfalls, and generally open the discussion around
hibernate.

You can find the document here (which anyone with the link can add comments
to):

https://docs.google.com/document/d/1L6b-gEUQcbRMfSuKIytMPlsZfa_q6HCZmmYtN4ysg1M

At this stage, we're mostly setting our focus to something similar to the
approach taken by OpenBSD's hibernate implementation. We're also thinking of
giving a lot of the responsibility to reloading the hibernated kernel to
loader(8), as opposed to e.g. Linux, which first boots a preliminary kernel
which then goes on to load the hibernated kernel.

But nothing is set in stone. We're mostly hoping to hear from people with prior
experience in this area, so feedback/comments are welcome!

Feedback received before the end of September will be easiest to incorporate.
Please add comments directly into the document shared above, or respond to this
email.

Thanks,
Aymeric on behalf of the FreeBSD Foundation