Re: FUSYN and RT

[Inaky Perez-Gonzalez <inaky@linux.intel.com>]

>>>>> Steven Rostedt <rostedt@goodmis.org> writes:

> On Fri, 2005-04-15 at 18:20 -0700, Inaky Perez-Gonzalez wrote:

>> Back to my example before: in fusyn, a user space lock is a kernel
>> space lock with a wrapper, that provides all that is necessary for
>> doing the fast path and handling user-space specific issues.

> ...

> So, to answer your question. Looking forward, I kind of see two
> different structures for locking.  The rt_mutex and something that
> is used by fusyn, then there being some common structure (or ops)
> that they both use to implement the PI.  But the implementation of
> how the locks work may as well be different. But this may not be the
> case, and there still be two structures but the fusyn just contain a
> rt_mutex lock to do the actual locking and the rest of the structure
> be used for showing information or what not back up to user
> space. This stuff wouldn't be necessary for the rt_mutex. We need to
> keep rt_mutex small since it is used all over the place.

I see--would the following fit your view?

This would be a kernel lock [from the fusyn patch, linux/fulock.h]:

	/** A fulock, mutex usable from the kernel. */
	struct fulock {
	        struct fuqueue fuqueue;
	        struct task_struct *owner;
	        unsigned flags;
	        struct plist olist_node;
	};

This has an in kernel API so you can use it from modules or kernel
code.

And this would be kernel representation of a user space lock [from
linux/fulock_kernel.h]:

	struct ufulock {
	        struct fulock fulock;
	        struct vlocator vlocator;
	        struct page *page;
	};

This is exposed via system calls with fast-path as an option.

This is basically the kernel lock that provides the functionality and
an structure to keep a tab to where the thing is in user space (hash
queues a la futex). The ops are hidden in fulock.fuqueue.ops [fuqueue
is the waitqueue--just for reference, from linux/fuqueue.h].

	/** A fuqueue, a prioritized wait queue usable from kernel space. */
	struct fuqueue {
	        spinlock_t lock;        
	        struct plist wlist;
	        struct fuqueue_ops *ops;
	};

-- 

Inaky