Re: [PATCH 4/6] xfs: kill the b_strat callback in xfs_buf

[Dave Chinner <david@fromorbit.com>]

On Sun, Jul 18, 2010 at 04:38:52PM -0400, Christoph Hellwig wrote:
> The b_strat callback is used by xfs_buf_iostrategy to perform additional
> checks before submitting a buffer.  It is used in xfs_bwrite and when
> writing out delayed buffers.  In xfs_bwrite it we can de-virtualize the
> call easily as b_strat is set a few lines above the call to
> xfs_buf_iostrategy.  For the delayed buffers the rationale is a bit
> more complicated:
> 
>  - there are three callers of xfs_buf_delwri_queue, which places buffers
>    on the delwri list:
>     (1) xfs_bdwrite - this sets up b_strat, so it's fine
>     (2) xfs_buf_iorequest.  None of the callers can have XBF_DELWRI set:
> 	- xlog_bdstrat is only used for log buffers, which are never delwri
> 	- _xfs_buf_read explicitly clears the delwri flag
> 	- xfs_buf_iodone_work retries log buffers only
> 	- xfsbdstrat - only used for reads, superblock writes without the
> 	  delwri flag, log I/O and file zeroing with explicitly allocated
> 	  buffers.
> 	- xfs_buf_iostrategy - only calls xfs_buf_iorequest if b_strat is
> 	  not set
>     (3) xfs_buf_unlock
> 	- only puts the buffer on the delwri list if the DELWRI flag is
> 	  already set.  The DELWRI flag is only ever set in xfs_bwrite,
> 	  xfs_buf_iodone_callbacks, or xfs_trans_log_buf.  For
> 	  xfs_buf_iodone_callbacks and xfs_trans_log_buf we require
> 	  an initialized buf item, which means b_strat was set to
> 	  xfs_bdstrat_cb in xfs_buf_item_init.
> 
> Conclusion: we can just get rid of the callback and replace it with
> explicit calls to xfs_bdstrat_cb.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

looks good.

Reviewed-by: Dave Chinner <david@fromorbit.com>

-- 
Dave Chinner
david@fromorbit.com

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