Re: [RFC] POSIX personality

[george anzinger <george@mvista.com>]

Dave McCracken wrote:
> 
> As part of improving support for POSIX multithreading I've been putting
> together some patches to allow more things to be shared between tasks.
> Right now this is accomplished via flags to clone() with one flag per
> resource to be shared.  This usually translates to a data structure pointed
> to out of task_struct, complete with reference count and lock.
> 
> In a discussion today an alternate idea was proposed by Ben LaHaise.  He
> suggested creating a POSIX personality, or execution domain.  This would
> take some pressure off the clone flag space as well as allowing some
> optimizations in the code. It could also be used in situations where
> POSIX-compatible behavior entails more than just sharing extra resources
> between tasks.
> 
> This would assume that the resources I'm sharing would only be useful for
> POSIX compatibility, but at this point it seems unlikely that anyone would
> want to share a subset of them.  The resources I'm currently working on
> include credentials, signals,  and timers, and there's a patch available
> for semaphore undo that could also be part of this mechanism.
> 
> Since you've made it this far my question to you all is this:  assuming
> that we do want improved POSIX compatibility does this sound like a
> reasonable way to add it?
> 
What you are proposing seem a bit vague.  I think that
CLONE_THREAD should group all the thread related stuff under
the one flag.  IMHO POSIX compatibility should not be off in
the corner as a step child, but rather should be the norm. 
The CLONE_THREAD flag would indicate to fork that it should
create a POSIX thread and set up the needed shared stuff.  I
rather image this to be a structure that each task_struct
points to, possibly with a usage count (but that is a
detail).  Each thread_struct would point to such a
structure, but processes that are not threaded would not be
sharing this area with other threads.

Is this close to what you had in mind?

-g
> 
> ======================================================================
> Dave McCracken          IBM Linux Base Kernel Team      1-512-838-3059
> dmccr@us.ibm.com                                        T/L   678-3059
> 
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-- 
George Anzinger   george@mvista.com
High-res-timers: 
http://sourceforge.net/projects/high-res-timers/
Real time sched:  http://sourceforge.net/projects/rtsched/
Preemption patch:
http://www.kernel.org/pub/linux/kernel/people/rml