Info about suspend-to-disk

[Conrad Meyer]

Hi Eric,

On Mon, Aug 22, 2016 at 8:41 PM, Eric McCorkle <eric at metricspace.net> wrote:
> Hi everyone,
>
> I'm gathering information in preparation for possibly working on
> suspend-to-disk functionality.  I have a fairly good idea of what it
> would take and one way to attack it.  The overall plan would look
> something like this:
>
> * Use dump functionality to write an entire OS image out to disk.  As
> this is a voluntary dump, it should be possible to go through the FS
> interface to produce a regular file.
>
> * Modify boot1 to check for saved images.  Load and resume if one exists.

That sort of thing should probably go in loader, not boot1.  (boot0-2
are just the MBR boot block(s), as I understand it; loader is the last
pre-OS stage and where most features live.)

> * Presumably there would need to be some new device methods added to do
> saving/reinitialization of devices.

Probably similar problems to kexec/kboot.  (That was a major roadblock
for kexec efforts, I believe.)  I think getting this right will be the
really challenging part.

> The major open questions for me are the following:
>
> * Is there/has there been significant work in this direction?
>
> * Is there perhaps a better strategy?
>
> * Do the codepaths currently exist to allow dump functionality to write
> to a regular file in the case of a voluntary dump, or would this need to
> be added?

That would have to be added.  You could maybe register a file
dumperinfo (as long as you're careful to prevent its use on
panic-during-suspend), but nothing does this yet.

> * What would be the most sensible default behavior for device
> hibernate/unhibernate methods?
>
> * Any other significant issues

Undoubtedly something will come up :-).

Best,
Conrad