[PATCH] news: Document recent dbus-vmstate changes

Marc-André Lureau marcandre.lureau at redhat.com
Wed Apr 1 17:21:18 UTC 2020


On Wed, Apr 1, 2020 at 6:40 PM Andrea Bolognani <abologna at redhat.com> wrote:
> On Wed, 2020-04-01 at 18:23 +0200, Michal Privoznik wrote:
> > +      <change>
> > +        <summary>
> > +          qemu: Support migration with SLIRP interface
> > +        </summary>
> > +        <description>
> > +          As <code>libslirp</code> evolves, so does QEMU. The recent change is
> > +          that instead of peer-to-peer connection between QEMU and
> > +          <code>slirp-helper</code> process a separate D-BUS bus is created.
> > +          This enables QEMU to migrate with a SLIRP interface.
> > +        </description>
> > +      </change>
> This looks reasonable enough to me, so
>   Reviewed-by: Andrea Bolognani <abologna at redhat.com>
> but let's maybe wait until tomorrow to push, in order to give
> Marc-André a chance to speak his mind.

Thanks. That's quite accurate, but it may be misinterpreted:

Networking data is still going through a 1-1 dgram unix socket.

D-Bus bus is used to communicate with the helper for RPC/management,
including migration.

After discussions, we decided to switch to a bus, as it permits other
tools, such as libvirt or others, to interact with the helpers easily.
A bus topology reduces the overall complexity for implementation and
debugging. This should slowly become the RPC standard for
"multi-process qemu"  in general. So libvirt will need a single
connection to the bus, and can then talk to the various helper
processes. Similarly for qemu or third-party (with security

Since the p2p dbus support was never actually used, I am not sure we
need to explain that there was a transition. Let me suggest:

qemu: Support migration with SLIRP helper interface

With QEMU 5.0, a new D-Bus backend allows migration of external
processes. When needed, libvirt will start a per-vm D-Bus bus, and
migrate the slirp-helper along with QEMU.

my 2c

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