[PATCH 16/27] xfs: avoid usage of struct xfs_dir2_block

[Dave Chinner]

On Fri, Jul 01, 2011 at 05:43:37AM -0400, Christoph Hellwig wrote:
> In most places we can simply pass around and use the struct xfs_dir2_data_hdr,
> which is the first and most important member of struct xfs_dir2_block instead
> of the full structure.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
....
> @@ -105,13 +105,13 @@ xfs_dir2_block_addname(
>  		return error;
>  	}
>  	ASSERT(bp != NULL);
> -	block = bp->data;
> +	hdr = bp->data;
>  	/*
>  	 * Check the magic number, corrupted if wrong.
>  	 */
> -	if (unlikely(be32_to_cpu(block->hdr.magic) != XFS_DIR2_BLOCK_MAGIC)) {
> +	if (unlikely(hdr->magic != cpu_to_be32(XFS_DIR2_BLOCK_MAGIC))) {

Took me a moment to realise what this does - turns the byte swap
into a compile-time operation rather than a runtime operation.
Nice.

Perhaps we should do that same optimisation in other magic number
checks around the place?

Looks good.

Reviewed-by: Dave Chinner <dchinner at redhat.com>
-- 
Dave Chinner
david at fromorbit.com