Changing back to per-thread credentials on Linux (fixing native AIO).

[Jeremy Allison]

On Wed, Jun 27, 2012 at 11:07:30AM -0700, Richard Sharpe wrote:
> 
> Well, I was thinking of the performance issues associated with
> maintaining per-process creds when you have multiple threads changing
> creds and the need to maintain that between change_to_user and
> change_to_root ...

Oh sure, it's very hard to use threads efficiently in a creds-per-process
environment for what smbd does.

However we should take advantage of the per-thread creds on Linux,
which is what this change allows us to easily do.

Jeremy.