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Re: [libvirt] Availability of libvirt-4.6.0 Release Candidate 2



On Wed, Aug 01, 2018 at 01:41:48PM +0200, Bjoern Walk wrote:
> Daniel P. Berrangé <berrange redhat com> [2018-08-01, 11:51AM +0100]:
> > On Tue, Jul 31, 2018 at 03:54:43PM +0200, Bjoern Walk wrote:
> > > Bjoern Walk <bwalk linux ibm com> [2018-07-31, 03:16PM +0200]:
> > > > I have not yet had the time to figure out what goes wrong, any ideas are welcome.
> > > 
> > > Ah, classic. The mocked virRandomBytes function is not endian-agnostic,
> > > generating a different interface name as expected by the test.
> > 
> > I'm not seeing why virRandomBytes is affected by endian-ness. It is simply
> > populating an array of bytes, so there's no endin issues to consider there.
> 
> Ahem, we are writing linearly to a byte array, of course this is
> dependend on the endianness of the architecture. The actual problem is
> that the mocked version does _not_ provide a random value, but a
> deterministic one, which is byte order reversed on big endianness.

There's no concept of reversed byte order when you're accessing an
array of bytes.  If you write elements 0, 1, 2, ...7, etc and then
the caller reads elements 0, 1,2, ..., 7 everything is fine.

Endianness only comes into play if you take that array of bytes
and then cast/assign it to a larger type were endianess is
relevant (eg int16/int32/int64)

eg

   char bytes[8];

   virRandomBytes(bytes, 8);

   uint64_t val = (uint64_t)bytes;

the problem in such a case isn't virRandomBytes, it is the cast
to the larger sized integer type.

> > Can you elaborate on the actual error messages you are getting from the
> > tests, and what aspect makes you think virRandomBytes is the problem ?
> 
> The name of the interface is wrong compared to what is explicitly
> expected in the test case:
> 
> 200         if (virAsprintf(&temp_ifacename,
> (gdb)
> 205         VIR_DEBUG("Attempting to create interface '%s' with IQN '%s'",
> (gdb) p temp_ifacename
> $1 = 0x1014320 "libvirt-iface-04050607"
> 
> > Seems more likely that it is something higher up the call stack.

That looks like it uses virRandomBits rather than virRandomBytes.


Regards,
Daniel
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