On Mon, Jan 30 2012 at 7:31pm -0500,
Martin K. Petersen <martin.petersen@xxxxxxxxxx> wrote:
> From: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx>
>
> The WRITE SAME command supported on some SCSI devices allows the same
> block to be efficiently replicated throughout a block range. Only a
> single logical block is transferred from the host and the storage device
> writes the same data to all blocks described by the I/O.
>
> This patch implements support for WRITE SAME in the block layer. The
> blkdev_issue_write_same() function can be used by filesystems and block
> drivers to replicate a buffer across a block range. This can be used to
> efficiently initialize software RAID devices, etc.
>
> Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
...
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index 2b461b4..19f4754 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -115,6 +115,85 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
> EXPORT_SYMBOL(blkdev_issue_discard);
>
> /**
> + * blkdev_issue_write_same - queue a write same operation
> + * @bdev: target blockdev
> + * @sector: start sector
> + * @nr_sects: number of sectors to write
> + * @gfp_mask: memory allocation flags (for bio_alloc)
> + * @buffer: pointer to buffer containing data to write
> + * @length: buffer length. Must be equal to bdev logical block size.
> + *
> + * Description:
> + * Issue a write same request for the sectors in question.
> + */
> +int blkdev_issue_write_same(struct block_device *bdev, sector_t sector,
> + sector_t nr_sects, gfp_t gfp_mask, void *buffer,
> + unsigned int length)
> +{
> + DECLARE_COMPLETION_ONSTACK(wait);
> + struct request_queue *q = bdev_get_queue(bdev);
> + unsigned int max_write_same_sectors;
> + struct bio_batch bb;
> + struct bio *bio;
> + int ret = 0;
> +
> + if (!q)
> + return -ENXIO;
> +
> + max_write_same_sectors = q->limits.max_write_same_sectors;
> +
> + if (max_write_same_sectors == 0)
> + return -EOPNOTSUPP;
> +
> + BUG_ON(length != bdev_logical_block_size(bdev));
Why require @length to be passed in if we can easily determine the only
correct length, via bdev_logical_block_size, locally?
Mike
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