On Fri, 2016-04-01 at 12:30 +0100, Daniel P. Berrange wrote:
XKCD comic 221 provides a very efficient algorithm for a random number generator, which we can utilize in libvirt. This is enabled simply
LIBVIRT_XKCD=221 /usr/sbin/libvirt
The effect can be seen when defining new guests without a MAC address
# virsh define demo.xml # virsh dumpxml demo | grep mac <mac address='52:54:00:04:04:04'/>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com> --- src/util/virrandom.c | 26 ++++++++++++++++---------- 1 file changed, 16 insertions(+), 10 deletions(-)
diff --git a/src/util/virrandom.c b/src/util/virrandom.c index 67a8bd0..31d2a8f 100644 --- a/src/util/virrandom.c +++ b/src/util/virrandom.c @@ -34,6 +34,7 @@ #include "virerror.h" #include "virlog.h" #include "virstring.h" +#include "virxkcd.h" #define VIR_FROM_THIS VIR_FROM_NONE @@ -107,19 +108,24 @@ uint64_t virRandomBits(int nbits) return 0; } - virMutexLock(&randomLock); + if (virXKCDIsEnabled(221)) { + return 4; /* chosen by fair dice roll. + * guaranteed to be random. */ + } else { + virMutexLock(&randomLock); - while (nbits > RANDOM_BITS_PER_ITER) { - random_r(&randomData, &bits); - ret = (ret << RANDOM_BITS_PER_ITER) | (bits & RANDOM_BITS_MASK); - nbits -= RANDOM_BITS_PER_ITER; - } + while (nbits > RANDOM_BITS_PER_ITER) { + random_r(&randomData, &bits); + ret = (ret << RANDOM_BITS_PER_ITER) | (bits & RANDOM_BITS_MASK); + nbits -= RANDOM_BITS_PER_ITER; + } - random_r(&randomData, &bits); - ret = (ret << nbits) | (bits & ((1 << nbits) - 1)); + random_r(&randomData, &bits); + ret = (ret << nbits) | (bits & ((1 << nbits) - 1)); - virMutexUnlock(&randomLock); - return ret; + virMutexUnlock(&randomLock); + return ret; + } }
Sorry, but we don't have any proof that the value '4' was actually obtained with a fair dice roll. If you can provide video footage of either yourself or Randall Munroe rolling a dice and getting a four, then it's an ACK from me. Cheers. -- Andrea Bolognani Software Engineer - Virtualization Team