[libvirt] RFC: Enable unprivileged SG_IO

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. 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. What I'm thinking about is to have a public API to tune the knob independantly with domain/driver, that means it's up to management apps to manage the knob's value, setting it to 1 before domain(s) starting, and 0 when no domain is using it. Any thoughts? Regards, Osier