Hypervisors and you!

Michael Torrie torriem at gmail.com
Tue Mar 26 08:49:04 MDT 2013

On 03/26/2013 01:03 AM, Dan Egli wrote:
> *I'm familiar with Qemu but last time I tried it I couldn't get any kind of
> networking. The directions I saw said I had to install a software bridge
> and make all sorts of network changes. Granted that was the Windows version
> of Qemu, but either way if it's being recommended now I hope the networking
> portion is easier now.*

Qemu's full computer emulation has either what they they call "user mode
networking" or the traditional bridge networking that you were fighting.
 User mode networking makes proxy connections on behalf of the virtual
machine, so it only supports udp and tcp/ip sockets.  No ICMP or other
raw protocols.  But it works for most things very well.  I guess Qemu
also supports a Slirp-style network connection, but that needs help from
the host sides in the form of a slirp daemon and it makes a point to
point connection that requires help from iptables to get out.

Qemu is also capable of another kind of emulation called "user mode
emulation" that works only with Linux apps.  What it does is run a linux
binary for one platform on a linux system running a different
architecture.  So the binary runs in an emulation environment with
kernel calls thunked through to the real kernel.  Typically you install
a mini distro along with the binary to provide all the supporting
libraries the binary needs.

Back when I had a PPC laptop running YellowDog, this let me run Adobe
Reader and Flash Plugin (x86-only) on my PPC laptop.  You could also use
it to run x86 wine on another platform like arm.  Or you could use it to
run arm binaries you were developing right on your x86 box.
Unfortunately with all the excitement surrounding full native vms, this
aspect of Qemu isn't talked about much, and may not be getting quite as
much love as it once got.

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