On Tue, Mar 22, 2016 at 14:49:42 +0000, Richard W.M. Jones wrote:
I got this error when trying to use /dev/urandom as a backend for virtio-rng. Is there a reason for that? Plain qemu allows you to specify /dev/urandom and seems to work OK.
There's a tetchy bugzilla on this subject:
The original implementation didn't do any verification. Later before releasing the feature it was decided that we should actually babysit the users in this case: commit 4932ef4502bc515a7d33e09e763118b7d763cd69 Author: Eric Blake <eblake@redhat.com> Date: Mon Mar 4 15:42:07 2013 -0700 rng: restrict passthrough names to known-good files There is some controversy[1] on the qemu list on whether qemu should have ever allowed arbitrary file name passthrough, or whether it should be restricted to JUST /dev/random and /dev/hwrng. It is always easier to add support for additional filenames than it is to remove support for something once released, so this patch restricts libvirt 1.0.3 (where the virtio-random backend was first supported) to just the two uncontroversial names, letting us defer to a later date any decision on whether supporting arbitrary files makes sense. Additionally, since qemu 1.4 does NOT support /dev/fdset/nnn fd passthrough for the backend, limiting to just two known names means that we don't get tempted to try fd passthrough where it won't work. [1]https://lists.gnu.org/archive/html/qemu-devel/2013-03/threads.html#00023 * src/conf/domain_conf.c (virDomainRNGDefParseXML): Only allow /dev/random and /dev/hwrng. * docs/schemas/domaincommon.rng: Flag invalid files. * docs/formatdomain.html.in (elementsRng): Document this. * tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.args: Update test to match. * tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.xml: Likewise. Peter