Re: Port forwarding for KVM

[Laine Stump <laine@xxxxxxxxx>]

On 04/12/2013 07:06 AM, 陳韋任 (Wei-Ren Chen) wrote:

Hi all,

  Let me illustrate what I want to do. I want to launch a QEMU
"inside" a KVM virtual machine, then get that QEMU's vnc output.
I am using libvirt 0.9.13 (`libvirtd --version`), and attach is
my vm's original config xml. Is there a simple way to achieve my goal?
I was told that iptable solution I found on the web is for "tap"
interface, and I can use "hostfwd" QEMU option if I use "user"
interface. For the latter approach, I basically follow this one [1]
with the QEMU cmdline option below:

  <qemu:commandline>
    <qemu:arg value='-net user,hostfwd=::5902-:5901'/>
  </qemu:commandline>

But virsh always keep saying:

  error: internal error Process exited while reading console log output:
  kvm: -net user,hostfwd=::5902-:5901: invalid option   

Aside from the problem Daniel pointed out in his reply, this is probably the *least* desirable way to get this functionality, and should only be used if you are unable to use any other network connection type.

What I am missing here? I also found there was a patch for user mode
port forwarding [2]. Does that mean I can write libvirt xml directly
to do port forwarding?

No, that patch "died in committee"; in general it's a good idea, but it needs to be done in a way that is useful for all types of interface, not just usermode. Unfortunately nobody has had the combination of enough time + enough motivation to carry it through.

 If so, could someone give me hint on how to
write one? The last question is, do I have to change the interface
type from "network" to "user" so that I can do port forwarding?

No, you don't. Please take a look here:

  http://wiki.libvirt.org/page/Networking#Forwarding_Incoming_Connections

Alternately (and a simpler solution), you could use a bridged or direct (macvtap) network connection for your guest, and then the guest would have an IP address directly on the physical network and no need to have any ports forwarded.

  Thanks in advance! :)

[1] http://snippets.webaware.com.au/snippets/running-qemu-with-port-redirection-through-libvirt/
[2] http://www.redhat.com/archives/libvir-list/2012-May/msg00538.html

Regards,
chenwj

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