Hi Ludovic, [email protected] (Ludovic Courtès) writes:
> I was looking at the wrong code: we’re using libuuid from util-linux, > which in turn uses getrandom(2). Since it doesn’t pass the > GRND_NONBLOCK flag, it ends up blocking forever because too little > entropy is available in the VM. > > The following patches work around that: > > 1. Parted now explicitly uses getrandom(2) with GRND_NONBLOCK instead > of libuuid’s ‘uuid_generate’, which is good enough for this > purpose. I’ll submit it upstream. > > 2. e2fsprogs is changed to use a libuuid that passes GRND_NONBLOCK. > It does the job, but it’s quite inelegant. I'm uncomfortable with this approach. I think that it's proper for uuid generation to block if there's not enough entropy. > Another approach I looked at was to seed the VM’s PRNG from /dev/hwrng, > which I thought was connected to the host via ‘virtio-rng-pci’, but I > get ENODEV while trying to read from /dev/hwrng in the guest like this: I much prefer this approach, where we seed the VM's PRNG from another source. > From 8aa37a4124db90a9991485477d1af85677c7fa1b Mon Sep 17 00:00:00 2001 > From: =?UTF-8?q?Ludovic=20Court=C3=A8s?= <[email protected]> > Date: Tue, 22 May 2018 17:36:35 +0200 > Subject: [PATCH 2/3] vm: Use a deterministic file system UUID in shared-store > VMs. > > * gnu/system/vm.scm (system-qemu-image/shared-store): Pass > #:file-system-uuid to 'qemu-image'. > --- > gnu/system/vm.scm | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/gnu/system/vm.scm b/gnu/system/vm.scm > index 09a11af86..b6561dfc7 100644 > --- a/gnu/system/vm.scm > +++ b/gnu/system/vm.scm > @@ -752,6 +752,13 @@ with the host. > When FULL-BOOT? is true, return an image that does a complete boot sequence, > bootloaded included; thus, make a disk image that contains everything the > bootloader refers to: OS kernel, initrd, bootloader data, etc." > + (define root-uuid > + ;; Use a fixed UUID so that 'mke2fs' doesn't wait for strong randomness > + ;; while generating a UUID. See <https://bugs.gnu.org/31268>. > + ;; XXX: Actually it doesn't help since 'mke2fs' calls 'uuid_generate' > + ;; anyway. How about fixing mke2fs so that if you specify a fixed UUID, it won't try to generate a random one? Would that be sufficient? Thanks, Mark
