[libvirt] RFC: Enable unprivileged SG_IO

[Paolo Bonzini]

Il 22/11/2012 15:11, Osier Yang ha scritto:
> 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.

I don't like it either, but I don't see any alternative...

> 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.

At this point, it's simpler to just let the admin do this in
/etc/rc.d/rc.local or in udev rules (which was my initial idea).

Paolo

> Any thoughts?
> 
> Regards,
> Osier