[libvirt] [RFC PATCH 0/5] ivshmem support

[Cam Macdonell]

On Mon, Aug 11, 2014 at 8:38 AM, Levente Kurusa <lkurusa at redhat.com> wrote:

> On Aug 06 2014, Wang Rui wrote:
> >On 2014/8/6 0:48, Maxime Leroy wrote:
> >> The following patches are an implementation proposal
> >> for the ivshmem device support in libvirt.
> >>
> >> Any feedback is welcome.
> >>
> >> Note:
> >>    SELinux is not supported (need to be done for the next
> >>    patchset version)
> >>
> >
> >Just some questiones:
> >Is there only one master at most on a host?
>
> Right now, qemu does not have any restriction on the number of masters
> on a host.
>
> >What will happen if two masters(in one VM or two VMS) on a host?
>
> By default, all ivshmem devices are 'master' unless specified to be
> 'peer' on the command line. The only difference between 'master' and
> 'peer' is that 'peer' blocks migration.
>
> My guess is that this mode-thing was a planned feature to solve
> migration problems. According to my understanding the following was
> meant to be:
>
> The guests using the same SHM are virtually grouped together, having
> one (and only one!) master guest, the rest being peer guests. On
> migration the guest-group can only be migrated to the same host and all
> together.
>
> The master guest will copy over the SHM. Before this happens the ivshmem
> devices are detached from the peer guests using PCI/ACPI hotplug. Once
> the master finishes the copy, the guests are migrated and the peers are
> reattached with a new fd pointing to the new shm object on the new host.
>
> So, to answer your question: My guess is that you can have as much
> master guests on the host, given that each master has a unique SHM.
>

Hello,

One master per SHM is the original intent.  The goal was to make migration
behaviour explicit for each guest.

Cam



> Thanks!
> Levente Kurusa
>
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