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

[Michael R. Hines]

On 11/15/2013 02:25 PM, Eric Blake wrote:
> On 11/15/2013 10:40 AM, Michael R. Hines wrote:
> > This is unrelated to RDMA - accessing the /dev/infiniband
> > device nodes is already supported by libvirt my modifying
> > the configuration file in /etc and that works just fine.
> http://wiki.qemu.org/Features/RDMALiveMigration states that you modify
> the .conf file to expose /dev/infiniband/rdma_cm and friends.  Are all
> of these devices read/write accessible to non-root?  Or is there going
> to be a problem if using user="qemu" group="qemu"?  (That is, merely
> exposing the devices through cgroup device ACL checking may be
> insufficient if you can't access the devices when not running root/root).

Yes, non-root access is working just fine. Keep in mind that QEMU is no
different than any other standard HPC application (like MPI programs)
which perform RDMA operations.

QEMU is simply another librdmacm/libibverbs user and it does
not require any special privileges to the device files.

> Libvirt can be patched so that the .conf file does not have to be edited
> (ie. change the defaults so that if cgroup_device_acl is not present in
> the conf file, the defaults could still let a domainaccess the
> /dev/infiniband devices).

That would be quite nice! Shall I include that in the next version
of my libvirt patch?

- Michael