Subject: Re: [RFC] Add support for semaphore-like structure with support
	for asynchronous I/O
From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: Andrew Morton <akpm@osdl.org>
Cc: linux-kernel@vger.kernel.org,
       Linux Filesystem Development <linux-fsdevel@vger.kernel.org>
In-Reply-To: <20050331161350.0dc7d376.akpm@osdl.org>
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	 <20050331161350.0dc7d376.akpm@osdl.org>
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Date: Thu, 31 Mar 2005 20:22:17 -0500
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to den 31.03.2005 Klokka 16:13 (-0800) skreiv Andrew Morton:
> Trond Myklebust <trondmy@trondhjem.org> wrote:
> >
> >  on den 30.03.2005 Klokka 18:17 (-0500) skreiv Trond Myklebust:
> >  > > Or have I misunderstood the intent?  Some /* comments */ would be appropriate..
> >  > 
> >  > Will do.
> > 
> >  OK. Plenty of comments added that will hopefully clarify what is going
> >  on and how to use the API. Also some cleanups of the code.
> 
> Ah, so that's what it does ;)
> 
> I guess once we have a caller in-tree we could merge this.  I wonder if
> there's other existing code which should be converted to iosems.

I can put it into the NFS client stream which feeds into the -mm kernel.
That will enable me to queue up the NFSv4 patches that depend on it
too...

> You chose to not use the aio kernel threads?

I thought I'd do that in a separate patch since the aio workqueue is
currently statically defined in aio.c.

> Does iosem_lock_and_schedule_function() need locking?  It nonatomically
> alters *lk_state.

iosem_lock_and_schedule_function() will always be called with the
iosem->wait.lock held, since it is a waitqueue notification function.

In practice it is called by iosem_unlock(). The call to wake_up_locked()
will trigger a call to __wake_up_common() which again tries the
notification function of each waiter on the queue until it finds one
that succeeds.

Cheers,
  Trond

-- 
Trond Myklebust <trond.myklebust@fys.uio.no>

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