>>> It is already migrated as part of virtio_rng_save's call to virtio_save. >>> On the loading side, virtio_rng_process condenses all requests into one >>> and chr_read fills in as many virtqueue buffers as possible from the >>> single request. >> >> Thanks! So this looks broken. The contract between virtio-rng and the rng >> backend is "one chr_read callback per one rng_backend_request_entropy", >> regardless of the request size. It guarantees that chr_read will get at >> least one byte, nothing else. If the one condensed request is bigger than >> what the backend is able to give at the moment, there may be unsatisfied >> virtio buffers left in the queue. >> >> One way of fixing this would be to have chr_read call virtio_rng_process >> if it ran out of backend data but not out of virtio buffers. Otherwise >> those buffers will be slowly drained by the rate limit timer, which is >> not optimal (especially in the absence of rate limit :)
Nice observation! And the commit you mention below seems to be the right way to fix it indeed. Amit, do you recall why this was done? > Basically, we could just revert this commit: > > commit 4621c1768ef5d12171cca2aa1473595ecb9f1c9e > Author: Amit Shah <amit.s...@redhat.com> > Date: Wed Nov 21 11:21:19 2012 +0530 > > virtio-rng: remove extra request for entropy > > If we got fewer bytes from the backend than requested, don't poke the > backend for more bytes; the guest will ask for more (or if the guest has > already asked for more, the backend knows about it via handle_input() I've now reviewed your patch more carefully, I will make some comments in reply to the patch directly. Paolo
