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Date: Sat, 1 May 2010 08:58:39 -0400
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 4/5] [PATCH] xfs: simplify buffer to transaction matching
Message-ID: <20100501125839.GA26342@infradead.org>
References: <20100418001041.865247520@bombadil.infradead.org>
	<20100418001058.677429475@bombadil.infradead.org>
	<20100420064155.GH15130@dastard>
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To: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>, xfs@oss.sgi.com

On Tue, Apr 20, 2010 at 04:41:55PM +1000, Dave Chinner wrote:
> Good start, but I think that it should use xfs_trans_first_item()
> and xfs_trans_next_item() rather than walking the descriptor
> table directly.

I tried implementing it, but it doesn't work.  We can call the buffer
matching routines on transactions that don't have any item linked to
it, which will cause xfs_trans_first_item to panic.  Compare this code
in xfs_trans_buf_item_match:

	for (licp = &tp->t_items; licp != NULL; licp = licp->lic_next) {
		if (xfs_lic_are_all_free(licp)) {
			ASSERT(licp == &tp->t_items);
			ASSERT(licp->lic_next == NULL);
			return NULL;
		}

		...
	}

to this in xfs_trans_first_item:

	licp = &tp->t_items;
        /*
	 * If it's not in the first chunk, skip to the second.
	 */
	if (xfs_lic_are_all_free(licp)) {
		licp = licp->lic_next;
	}

	/*
	 * Return the first non-free descriptor in the chunk.
	 */
	ASSERT(!xfs_lic_are_all_free(licp));

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