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Re: [Qemu-devel] Re: [PATCH 0/4] net-bridge: rootless bridge support for

From: Anthony Liguori
Subject: Re: [Qemu-devel] Re: [PATCH 0/4] net-bridge: rootless bridge support for qemu
Date: Wed, 04 Nov 2009 13:48:01 -0600
User-agent: Thunderbird (X11/20090825)

Michael S. Tsirkin wrote:
On Tue, Nov 03, 2009 at 06:28:01PM -0600, Anthony Liguori wrote:
This series solves a problem that I've been struggling with for a few years now.
One of the best things about qemu is that it's possible to run guests as an
unprivileged user to improve security.  However, if you want to have your guests
communicate with the outside world, you're pretty much forced to run qemu as

At least with KVM support, this is probably the most common use case which means
that most of our users are running qemu as root.  That's terrible.

We address this problem by introducing a new network backend: -net bridge.  This
backend is less flexible than -net tap because it relies on a helper with
elevated privileges to do the heavy lifting of allocating and attaching a tap
device to a bridge.  We use a special purpose helper because we don't want
to elevate the privileges of more generic tools like brctl.

>From a user perspective, to use bridged networking with a guest, you simply 

  qemu -hda linux.img -net bridge -net nic

And assuming a bridge is defined named qemubr0 and the administrator has setup
permissions accordingly, it will Just Work.  My hope is that distributions will
do this work as part of the qemu packaging process such that for most users,
the out-of-the-box experience will also Just Work.

More details are included in individual patches.  I broke up the helper into
a series of patches to improve reviewabilty.

Would raw backend attached to a bridge mostly do the same?

Well it doesn't really help with the issue of privileges which is what this series is really about.


Anthony Liguori

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