Howdy,
I've been working on migration for QEMU and have run into a snag. I've
got a non-live migration patch that works quite happily[1]. I modified
the save/restore code to not seek at all, and then basically pipe a save
over a pipe to a subprocess (usually, ssh).
Conceptually, adding support for live migration is really easy. All I
think I need to do is extend the current code, to have a pre-save hook
that is activated before the VM is stopped. This hook will be called
until it says it's done and then the rest of the save/load handlers are
invoked. At first, I'm just going to do a pre-save handler for RAM
which should significantly reduce the amount of down time. I think the
only other device we'll have to handle specially is the VGA memory but
I'm happy to ignore that for now.
So, all I really need is to be able to track which pages are dirtied. I
also need the a method to reset the dirty map.
I started looking at adding another map like phys_ram_dirty. That seems
to work for some of the IO_MEM_RAM pages, but not all. My initial
thought is that all memory operations should go through one of the
st[bwl]_phys functions but that doesn't seem to be the case.
Can anyone provide me with some advice on how to do this? Am I right in
assuming that all IO will go through some function?
[1] http://hg.codemonkey.ws/qemu-pq/?f=758c26c82f52;file=qemu-migration.diff
Thanks,
Anthony Liguori
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