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Re: [libvirt] FreeBSD, no gcc present libvirt build issue



On 08/29/2013 10:03 AM, Daniel P. Berrange wrote:

>> I think I can fix libvirt to work around the boneheaded decision;
>> basically, since we cannot trust the full range of random_r to be evenly
>> distributed, I will have to tweak libvirt's call to truncate every call
>> to random_r to a subset of bits that are more likely to be evenly
>> distributed (maybe by shifting off the most- and least-significant bits
>> returned, and only using 28 instead of 31 bits of randomness per call).
>>  But I would MUCH rather prefer that FreeBSD revisit their decision, and
>> guarantee that random output be evenly distributed across the full 31
>> bits to begin with.
> 
> Since gnulib has a working random_r() function can we just make
> gnulib replace the boneheaded freebsd impl ?

Huh - the glibc man pages state that random_r returns RAND_MAX bits.
random_r is a glibc extension: POSIX only requires rand(), rand_r(), and
random(); but even with random(), POSIX has no requirements that it be
related to RAND_MAX - so the fact that glibc equates random()/random_r()
with RAND_MAX is also a glibc extension.

I guess that means we should't be worrying about RAND_MAX in the first
place, as it is tied to the (potentially algorithmically weaker) rand(),
and need not have any bearing on the fact that we already use gnulib's
random_r().

I'll play around with a patch.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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