[libvirt] RFC: Enable unprivileged SG_IO

[Osier Yang]

On 2012年11月22日 22:20, Paolo Bonzini wrote:
> 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).

Isn't an API helpful in this case? The apps will want to manage
it anyway.

Regards,
Osier