linux-kernel - Re: [PATCH 1/6] Extend completions to provide XFS object flush requirements

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Date:	Thu, 26 Jun 2008 21:21:33 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	xfs@....sgi.com, matthew@....cx, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] Extend completions to provide XFS object flush
	requirements

On Thu, Jun 26, 2008 at 03:46:36AM -0400, Christoph Hellwig wrote:
> On Thu, Jun 26, 2008 at 02:41:12PM +1000, Dave Chinner wrote:
> > XFS object flushing doesn't quite match existing completion semantics.  It
> > mixed exclusive access with completion. That is, we need to mark an object as
> > being flushed before flushing it to disk, and then block any other attempt to
> > flush it until the completion occurs.
> > 
> > To do this we introduce:
> > 
> > void init_completion_flush(struct completion *x)
> > 	which initialises x->done = 1
> > 
> > void completion_flush_start(struct completion *x)
> > 	which blocks if done == 0, otherwise decrements done to zero and
> > 	allows the caller to continue.
> > 
> > bool completion_flush_start_nowait(struct completion *x)
> > 	returns a failure status if done == 0, otherwise decrements done
> > 	to zero and returns a "flush started" status. This is provided
> > 	to allow flushing to begin safely while holding object locks in
> > 	inverted order.
> > 
> > This replaces the use of semaphores for providing this exclusion
> > and completion mechanism.
> 
> Given that the only API call shared with normal completions is
> complete() I'd rather make this a primitive of it's own, even if
> internally implemented as completions.

Ok, so that involves exactly what? A new header file, a new API name
(ideas anyone?) and kerneldoc comments?

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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