Il 27/09/2013 10:36, Michael Ellerman ha scritto: > So have the host kernel read from the hwrng, export it to userspace via > a char device, which is then read by qemu, which then copies it back > into the host kernel, which can then give it to the guest. > > Or from the guest perspective, instead of a cheap switch to host real > mode and back - a full switch to kernel virtual, then to user, back to > kernel, back to user, back to kernel, back to guest. > > Frankly I can't see why that is a superior option?
Because this is not a fast path at all. Doing things in QEMU lets people test and configure the paravirtualized hwrng even if they do not have a hwrng in the host, and even if they are running with emulation (TCG) instead of KVM. But as I mentioned in the kernel thread, perhaps you do not need the hypercall at all if virtio-rng is enough (it should be for Linux guests). Paolo
