Resuming from a crashdump

Joerg Sonnenberger joerg at britannica.bec.de
Tue Jan 25 14:33:29 PST 2005


On Tue, Jan 25, 2005 at 09:45:43PM +0000, Steven Smith wrote:
> Also, have you ever looked at the live migration stuff Xen uses?  The
> aim here is to move a running operating system from one machine to
> another with minimal downtime.  Essentially, you just start copying
> pages across willy nilly, keeping track of pages which get dirtied.
> After every page has been copied, you go back over the list of dirty
> pages, and just migrate them, and so on, until you stop making any
> progress.  At that point, you stop the guest operating system and copy
> everything that's left in one big go, and start it going on the new
> machine.

The situation of suspending / migrating a guest OS under any
virtualisation software is *much* easier, because it is just the same
amount of state as a normal userland process has. Without knowing
all the internals of Xen, it should be as easy as saving the config of
the virtual network device, the console settings, the page table and
the actual memory image.

For a normal operating system (e.g. Xen itself), you have to deal with
physical hardware which has to be re-synchronised with the kernel.
This has to be done for ACPI S3/S4 support anyway.
I don't know the state of suspend / resume hooks in FreeBSD 5/6,
but if they are all inplace (esp. for interrupt management and the
like), doing a special coredump is functional similiar to what do
with ACPI S3.

Joerg


More information about the freebsd-hackers mailing list