Eric Blake <ebl...@redhat.com> writes: > Stefan Berger and I discovered on IRC that virtio-rng is unable to > support fd passing. We attempted: > > qemu-system-x86_64 ... -add-fd set=4,fd=34,opaque=RDONLY:/dev/urandom > -object rng-random,id=rng0,filename=/dev/fdset/4 -device > virtio-rng-pci,rng=rng0,bus=pci.0,addr=0x6
Why are you using th rng-random backend instead of the rng-egd backend? You can pass chardevs to the egd backend. It's really not a good idea to pass a fd via rng-rangom. Regards, Anthony Liguori > > qemu-system-x86_64: -device virtio-rng-pci,rng=rng0,bus=pci.0,addr=0x6: > Could not open '/dev/fdset/4' > > Looks like this code is the culprit, in backends/rng-random.c: > > static void rng_random_opened(RngBackend *b, Error **errp) > { > RndRandom *s = RNG_RANDOM(b); > > if (s->filename == NULL) { > error_set(errp, QERR_INVALID_PARAMETER_VALUE, > "filename", "a valid filename"); > } else { > s->fd = open(s->filename, O_RDONLY | O_NONBLOCK); > > For fd passing to work, we have to use qemu_open() instead of raw > open(). Is there any way to enforce that all files being opened by qemu > go through the appropriate qemu_open() wrapper? > > Meanwhile, we have a quandary on the libvirt side of things: qemu 1.4 > supports fd passing in general, but does not support it for rng. I > guess the same is true for -blockdev - we don't (yet) have a way to do > fd passing for backing files. Do we need some sort of QMP command that > will let libvirt query for a particular device whether that device is > known to support fd passing, so that libvirt can use fd passing for all > supported devices, while falling back to older direct open()s, and to > know which instance of qemu can safely have open() blocked at the > SELinux or syscall blacklist level? > > -- > Eric Blake eblake redhat com +1-919-301-3266 > Libvirt virtualization library http://libvirt.org