[libvirt] RFC: Enable unprivileged SG_IO

[Daniel P. Berrange]

On Thu, Nov 22, 2012 at 10:11:01PM +0800, Osier Yang wrote:
> Hi,
> 
> http://lwn.net/Articles/524720/ introduces new sysfs knob
> (unpriv_sgio) for SCSI device to allow the unprivileged SG_IO.
> 
> I don't have solid thought on how the libvirt interface should
> be yet. It shouldn't be a XML entry of disk device, as the device
> can be shared by multiple guests, and the configuration should
> be kept same for all of them, having a XML entry for it will
> make things a mess.

IMHO it should be an XML entry of the disk device. If the same
device is then given to multiple guests, libvirt has to validate
that they all have the same setting in this respect.

> 
> What Paolo suggested is to add an entry in qemu.conf, just
> like "cgroup_device_acl":
> 
> sgio_device_acl = [ "/dev/sda" ]
> 
> When libvirtd starting, set the sysfs knob "unpriv_sgio" of
> the devices listed to 1, and 0 when libvirtd exists.
> 
> I don't quite agree with this approach, as entries in qemu.conf
> generally should be configuration for the whole qemu driver,
> however, the SG_IO setting is at the device layer, or not
> higher than guest layer.

This is fundamentally guest configuration IMHO,not system
configuration, so qemu.conf is the wrong place for it.

Regards,
Daniel
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