Re: [PATCH 13/14] target/rd: Add DIF protection into rd_execute_rw

[Sagi Grimberg <sagig@mellanox.com>]

On 1/8/2014 10:36 PM, Nicholas A. Bellinger wrote:
> From: Nicholas Bellinger <nab@linux-iscsi.org>
>
> This patch adds support for DIF protection into rd_execute_rw() code
> for WRITE/READ I/O using sbc_dif_verify_[write,read]() logic.
>
> It also adds rd_get_prot_table() for locating protection SGLs
> assoicated with the ramdisk backend device.
>
> Cc: Martin K. Petersen <martin.petersen@oracle.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Hannes Reinecke <hare@suse.de>
> Cc: Sagi Grimberg <sagig@mellanox.com>
> Cc: Or Gerlitz <ogerlitz@mellanox.com>
> Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
> ---
>   drivers/target/target_core_rd.c |   67 +++++++++++++++++++++++++++++++++++++++
>   1 file changed, 67 insertions(+)
>
> diff --git a/drivers/target/target_core_rd.c b/drivers/target/target_core_rd.c
> index dd99844..3fd51eb 100644
> --- a/drivers/target/target_core_rd.c
> +++ b/drivers/target/target_core_rd.c
> @@ -363,6 +363,26 @@ static struct rd_dev_sg_table *rd_get_sg_table(struct rd_dev *rd_dev, u32 page)
>   	return NULL;
>   }
>   
> +static struct rd_dev_sg_table *rd_get_prot_table(struct rd_dev *rd_dev, u32 page)
> +{
> +	struct rd_dev_sg_table *sg_table;
> +	u32 i, sg_per_table = (RD_MAX_ALLOCATION_SIZE /
> +				sizeof(struct scatterlist));
> +
> +	i = page / sg_per_table;
> +	if (i < rd_dev->sg_prot_count) {
> +		sg_table = &rd_dev->sg_prot_array[i];
> +		if ((sg_table->page_start_offset <= page) &&
> +		     (sg_table->page_end_offset >= page))
> +			return sg_table;
> +	}
> +
> +	pr_err("Unable to locate struct prot rd_dev_sg_table for page: %u\n",
> +			page);
> +
> +	return NULL;
> +}
> +
>   static sense_reason_t
>   rd_execute_rw(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
>   	      enum dma_data_direction data_direction)
> @@ -377,6 +397,7 @@ rd_execute_rw(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
>   	u32 rd_page;
>   	u32 src_len;
>   	u64 tmp;
> +	sense_reason_t rc;
>   
>   	if (dev->rd_flags & RDF_NULLIO) {
>   		target_complete_cmd(cmd, SAM_STAT_GOOD);
> @@ -399,6 +420,29 @@ rd_execute_rw(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
>   			data_direction == DMA_FROM_DEVICE ? "Read" : "Write",
>   			cmd->t_task_lba, rd_size, rd_page, rd_offset);
>   
> +	if ((cmd->se_cmd_flags & SCF_PROT) && se_dev->dev_attrib.pi_prot_type &&
> +	    data_direction == DMA_TO_DEVICE) {
> +		sector_t sector = cmd->data_length / se_dev->dev_attrib.block_size;
> +		struct rd_dev_sg_table *prot_table;
> +		struct scatterlist *prot_sg;
> +		u32 prot_offset, prot_page;
> +
> +		tmp = cmd->t_task_lba * se_dev->prot_length;
> +		prot_offset = do_div(tmp, PAGE_SIZE);
> +		prot_page = tmp;
> +
> +		prot_table = rd_get_prot_table(dev, prot_page);
> +		if (!prot_table)
> +			return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
> +
> +		prot_sg = &prot_table->sg_table[prot_page - prot_table->page_start_offset];
> +
> +		rc = sbc_dif_verify_write(cmd, cmd->t_task_lba, sector, 0,
> +					  prot_sg, prot_offset);
> +		if (rc)
> +			return rc;
> +	}
> +
>   	src_len = PAGE_SIZE - rd_offset;
>   	sg_miter_start(&m, sgl, sgl_nents,
>   			data_direction == DMA_FROM_DEVICE ?
> @@ -460,6 +504,29 @@ rd_execute_rw(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
>   	}
>   	sg_miter_stop(&m);
>   
> +	if ((cmd->se_cmd_flags & SCF_PROT) && se_dev->dev_attrib.pi_prot_type &&
> +	    data_direction == DMA_FROM_DEVICE) {
> +		sector_t sector = cmd->data_length / se_dev->dev_attrib.block_size;
> +		struct rd_dev_sg_table *prot_table;
> +		struct scatterlist *prot_sg;
> +		u32 prot_offset, prot_page;
> +
> +		tmp = cmd->t_task_lba * se_dev->prot_length;
> +		prot_offset = do_div(tmp, PAGE_SIZE);
> +		prot_page = tmp;
> +
> +		prot_table = rd_get_prot_table(dev, prot_page);
> +		if (!prot_table)
> +			return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
> +
> +		prot_sg = &prot_table->sg_table[prot_page - prot_table->page_start_offset];
> +
> +		rc = sbc_dif_verify_read(cmd, cmd->t_task_lba, sector, 0,
> +					 prot_sg, prot_offset);
> +		if (rc)
> +			return rc;
> +	}
> +
>   	target_complete_cmd(cmd, SAM_STAT_GOOD);
>   	return 0;
>   }

I wander how we can skip  sbc_dif_verify_xxxx if the transport already 
offloaded DIF verify.
I think that the transport should signal the core layer that it is able 
to offload DIF (ADD/STRIP/PASS/VERIFY), in which case the core should 
turn off the backstore DIF verify emulation to sustain performance. I 
assume that if backstore DIF verify is offloaded as well it does not 
really matter.

Sagi.