On 08/09/15 07:15, David Gibson wrote: > On Tue, Sep 08, 2015 at 03:03:16PM +1000, Sam Bobroff wrote: >> On Tue, Sep 01, 2015 at 12:53:26PM +0200, Thomas Huth wrote: >>> On 01/09/15 02:38, David Gibson wrote: >>>> On Mon, Aug 31, 2015 at 08:46:01PM +0200, Thomas Huth wrote: >>>>> From: Michael Ellerman <mich...@ellerman.id.au> >>>>> >>>>> Some powerpc systems have support for a hardware random number generator >>>>> (hwrng). If such a hwrng is present the host kernel can provide access >>>>> to it via the H_RANDOM hcall. ... >> What if we set up another backend that just enables the hcall in KVM? > > I think that's basically the right approach. > > It can't quite be a "backend" as such, since the in-kernel hcall can > only supply H_RANDOM; it can't supply random for other purposes like > virtio-rng, which the general qemu rng backends can. > > So I'd suggest two options controlling H_RANDOM: > usekvm : boolean [default true] > Whether to enable the in-kernel implementation if > available > backend : ref to rng backend object [no default] > Backend to use if in-kernel implementation is > unavailable or disabled. > > At this point rather than just implementing them as discrete machine > options, I suspect it will be more maintainable to split out the > h-random implementation as a pseudo-device with its own qdev and so > forth. We already do similarly for the RTAS time of day functions > (spapr-rtc).
I gave that I try, but it does not work as expected. To be able to
specify the options, I'd need to instantiate this device with the
"-device" option, right? Something like:
-device spapr-rng,backend=rng0,usekvm=0
Now this does not work when I use TYPE_SYS_BUS_DEVICE as parent class
like it is done for spapr-rtc, since the user apparently can not plug
device to this bus on machine spapr (you can also not plug an spapr-rtc
device this way!).
The spapr-vlan, spapr-vty, etc. devices are TYPE_VIO_SPAPR_DEVICE, so I
also tried that instead, but then the rng device suddenly shows up under
/vdevice in the device tree - that's also not what we want, I guess.
So I am currently not sure whether this is the right approach. Any
recommendations? Or shall I stick with the machine option?
Thomas
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