Re: When I boot two virtio-rng devices, guest will hang

[Amos Kong <akong@redhat.com>]

3.16 (guest hangs with two rng devices)
3.16 + quick fix (can startup with two rng devices) (hotplug issue 1 + hotplug issue 2 exist)
lates torvalds/linux.git + amit 4 patches (can startup with two rng devices) (only hotplug issue 2 exists)

However, the 4 patches also fixed the hang issue, the hotplug issue was fixed a little.
The hotplug issue is effected by the backend, or maybe it's not a real issue, because
the rng device can be hot-removed after dd process is killed.


Hotplug issue 1:
  1. boot up guest with two rng device (rng0 uses /dev/urandom, rng1 uses /dev/random)
  2. read data by dd in guest
  3 (option 1). hot-remove rng0, then hot-remove rng1 -> result: _only rng1_ can't be removed until dd process is killed
  3 (option 2). hot-remove rng1, then hot-remove rng0 -> result: two devices can be removed successfully, dd process will exit automatically.

  If we use /dev/urandom for rng0 and rng1, _rng0 & rng1_ can be removed, dd process will exit automatically.

Hotplug issue 2:
  If we use /dev/random for rng0 and rng1, _rng0 & rng1_ can't be removed until dd process is killed.

Hotplug issue 3:
  If we use /dev/random for rng0 and rng1, _only rng1_ can't be removed until dd process is killed.


(The difference between /dev/random and /dev/urandom is the speed.)

Thanks, Amos