[libvirt] [RFC PATCH] Add Qemu Network Helper

[Eric Blake]

On 05/10/2012 09:15 AM, rmarwah at linux.vnet.ibm.com wrote:
> From: Richa Marwaha <rmarwah at linux.vnet.ibm.com>
> 
> QEMU has a new feature which allows QEMU to execute under an unprivileged user ID and still be able to add a tap device to a Linux network bridge. Below is
> the link to the QEMU patches for the bridge helper feature:
> 
> http://lists.gnu.org/archive/html/qemu-devel/2012-01/msg03562.html
> 
> The existing libvirt tap network device support for adding a tap device to a bridge (-netdev tap) works only when connected to a libvirtd instance running
> as the privileged system account 'root'.  When connected to a libvirtd instance running as an unprivileged user (ie. using the session URI) creation of
> the tap device fails as follows:
> 
> error: Failed to start domain F14_64 error: Unable to create tap device vnet%d: Operation not permitted
> 
> With this support, creating a tap device in the above scenario will be possible.  Additionally, hot attaching a tap device to a bridge while running when
> connected to a libvirtd instance running as an unprivileged user will be possible.
> 
> Signed-off-by: Richa Marwaha <rmarwah at linux.vnet.ibm.com>
> Signed-off-by: Corey Bryant<coreyb at linux.vnet.ibm.com>
> ---
>  src/qemu/qemu_command.c |   38 +++++++++++++++++++++++++-------------
>  src/qemu/qemu_command.h |    1 +
>  src/qemu/qemu_hotplug.c |   19 +++++++++++--------
>  3 files changed, 37 insertions(+), 21 deletions(-)

Being a new feature, I think this is too late for inclusion in 0.9.12,
but looks like a very nice feature to have post-release!

I didn't spot anything obviously wrong with the code.

Who is responsible for setting up the qemu bridge helper?  Is the error
message when the bridge helper is not available (qemu too old, or helper
is not configured to run, ...) sensible, or does libvirt need an
additional qemu_capabilities.h patch to probe for the bridge helper so
that libvirt can give a sane error message?

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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