FreeBSD disk hibernation - Was: Resuming from a crashdump

[João Carlos Mendes Luís]

Bruce M Simpson wrote:
> On Mon, Jan 24, 2005 at 07:37:34PM -0600, Ryan Sommers wrote:
> 
>>My little knowledge on this subject aside. I'd love to have full 
>>suspend/resume functionality. It'd make my life as a mobile freebsd user 
>>much much easier. However, I wouldn't want it at the expense of every 
>>kernel. It would need to be something completely modular.
> 
> 
> I think what we're also looking at is aborting any pending bus-mastering
> transactions. This could probably be done as a part of the newbus
> suspend/resume routines for bus and device drivers, but it also means
> that the other entry points need to be able to deal with the carpet
> being dragged out from under them like this.

     As I said, the first step should be to enter a pre-suspend state, 
where only hard disk devices should be kept alive.  All other devices 
should be sleeping then, and so there will be no pending requests.

> In the case of a networking driver, particularly Ethernet, things are
> somewhat easier, and the more help you get from the hardware the better;
> but some cards like those based around ATM SARS just plain aren't designed
> to deal with the carpet being dragged out - they expect to keep rolling
> through their descriptor rings, segmenting and transmitting what they see.

    The carpet will not be dragged out.  The card wil be specifically 
shut down before this.   ;-)

     Of course, a techo-nerd-maniac could devise some form of network 
hibernating, or a NFS based hibernate file.  Just like crash dump, I 
don't think this is possible or even necessary.

> If we could take a clean subsystem-by-subsystem approach to marshaling
> kernel state to disk, that would be good. What gives me particular pain
> here is dealing with things like the filesystem. How does one deal with
> open files, etc, with pending I/O?

     There's no need to deal with it!  Just save the whole kernel core!

                                         Jonny

-- 
João Carlos Mendes Luís - Networking Engineer - jonny at jonny.eng.br