[OpenAFS-devel] Making supergroups default to on

[Simon Wilkinson]

On 28 Dec 2012, at 19:20, Andrew Deason wrote:
>=20
> I'm not sure if that's really an absolute requirement, though. The =
'code
> quality issues' that I remember were just the opinions of a few people
> that would make them uneasy about turning it on. I don't recall anyone
> trying very hard to get the default changed, so maybe that's all it
> takes.

There were/are a number of different issues in the supergroups code. =
There are aliasing issues throughout, some of which could be easily =
fixed by inserting memcpy's rather than just using casts/assignments, =
but there are others that require far more in depth analysis. This =
second set of aliasing problems are mainly confined to the caching code, =
rather than the supergroups code itself. It would certainly be possible =
to either disable caching, or rework that code, whilst having the ubik =
database format remain unchanged.

The other major issue is that there is bit twiddling in the caching code =
which makes assumptions about endianness, and about word size. I think =
we have now caught all of these problems - but certainly with the 1.4 =
series you couldn't safely run supergroups on a 64 bit machine.

Cheers,

Simon.