Re: [Qemu-devel] [PATCH v3 for-1.7] rdma: rename 'x-rdma' => 'rdma'

[Daniel P. Berrange]

On Wed, Nov 06, 2013 at 01:59:14PM -0500, address@hidden wrote:
> From: "Michael R. Hines" <address@hidden>
> 
> As far as we can tell, all known bugs have been fixed:

[snip]

> 3. Libvirt patches are ready

[snip]

> Objections?

There was a first round of patches posted to the libvirt list back
in July, but those were rejected since QEMU side was still in flux.

More seriously though, from discussions at the KVM Forum it sounds
like there is a significant problem in actually using the RDMA
code. Unfortunately I can't remember who I was talking with about
it, but I was told that it requires the QEMU process to run as root
in order to talk to some of the kernel interfaces, and requires
manual updates to the cgroups device ACL to allow QEMU access to
some RMDA related device nodes.

For this to be supportable in libvirt, we need this to work when
QEMU is running as an unprivileged user/group ID. If access to
any privileged resources is required, then there needs to be a
way to get privilege separation. Either libvirtd would need to
change file ownership to grant QEMU access to resources, or
libvirtd would need to open the resources & pass a FD across to
QEMU. Running QEMU as root is a non-starter.

I don't recall any new version of the patches being posted since
then to address this problem, so from the libvirt POV I don't
think this is ready, unelss I was mis-informed about this permission
problem.

Regards,
Daniel
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