On Mon, Feb 11, 2019 at 04:03:57PM +0000, Dr. David Alan Gilbert wrote:
> * Yury Kotov (yury-ko...@yandex-team.ru) wrote:
> > Hi,
> >
> > The series adds a migration capability, which allows to skip shared RAM
> > blocks
> > during the migration. It's useful for fast local migration. E.g. to update
> > QEMU
> > for the running guests.
> >
> > Usage example:
> > 1. Start source VM:
> > qemu-system-x86 \
> > -m 4G \
> > -object
> > memory-backend-file,id=mem0,size=4G,share=on,mem-path=/dev/shm/mem0 \
> > -numa node,memdev=mem0 \
> > -qmp unix:/tmp/qemu-qmp-1.sock,server,nowait \
> >
> > 2. Start target VM:
> > qemu-system-x86 \
> > -m 4G \
> > -object
> > memory-backend-file,id=mem0,size=4G,share=on,mem-path=/dev/shm/mem0 \
> > -numa node,memdev=mem0 \
> > -qmp unix:/tmp/qemu-qmp-2.sock,server,nowait \
> > -incoming defer
> >
> > 3. Enable ignore-external capability on both VMs:
> > { "execute": "migrate-set-capabilities" , "arguments":
> > { "capabilities": [ { "capability": "x-ignore-external", "state": true
> > } ] } }
> >
> > 4. Start migration.
> >
> > Another use case I keep in mind is to migrate to file. Usage is very
> > similar.
>
> Hi,
> I've cc'd in Eric, Lai and Peter, all who were asking for something
> similar last year; can you all confirm this patch does what you need or
> can work with what you needed to do?
x-ignore-external is a global setting so affects all memory-backend-file
instances. The obvious question is where there is any reasonable/conceivable
scenario in which QEMU would have multiple "-object memory-backend-file"
intsances and it be neccessary/desirable to migrate some, but skip migrate
of others ?
Could there ever be a device backend which is using a memory region
to communicate with an external process, where you would need to have
a new instance for the migration target QEMU, and explicitly not reuse
the source QEMU's memory-backend-file storage ?
Regards,
Daniel
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