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Re: [PATCH 1/6] Extend completions to provide XFS object flush requireme

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH 1/6] Extend completions to provide XFS object flush requirements
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 26 Jun 2008 21:21:33 +1000
Cc: xfs@xxxxxxxxxxx, matthew@xxxxxx, linux-kernel@xxxxxxxxxxxxxxx
In-reply-to: <20080626074636.GB7064@xxxxxxxxxxxxx>
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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@xxxxxxxxxxxxx


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