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

[Richard Sharpe]

On Wed, Jun 27, 2012 at 10:08 AM, Jeremy Allison <jra at samba.org> wrote:
> On Wed, Jun 27, 2012 at 10:00:17AM -0700, Richard Sharpe wrote:
>> On Wed, Jun 27, 2012 at 9:51 AM, Jeremy Allison <jra at samba.org> wrote:
>> >
>> > It also makes it much easier to proceed
>> > with the threaded aio open code I was working on,
>> > as now I can remove all the ugly race-condition
>> > handling code I was figting with, as we
>> > know that any thread can set its own credentials
>> > independently, ensuring no security issues
>> > on file create - but that's patch for another
>> > day :-).
>>
>> Does this also mean that the pre-forked smbds with each smbd handling
>> many connections will also work on Linux, since we are using Linux'
>> ability to do per-thread credentials in violation of POSIX?
>
> Well that would always have worked on any
> POSIX system as smbd notes what network uid
> the request came in on and changes to the
> appropriate POSIX credentials before acting
> on their behalf. The lost-wakeup glibc-aio
> issue was the only place we were depending
> on per-thread credentials but that was
> without explicitly knowing we needed them, as the
> glibc aio implementation using threads
> is a hidden internal detail (if you get
> my meaning :-).
>
> Fixing the lost wakeup bug and explicitly
> acknowleging we have per-thread creds allows
> us to take advantage of this to do optimizations
> on this (these? What about *BSDs ?) platforms
> that aren't easily done when you only have POSIX
> per-process creds.

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 ...

-- 
Regards,
Richard Sharpe
(何以解憂？唯有杜康。--曹操)