Re: [PATCH v3 4/5] target: Fix sbc_dif_generate() and sbc_dif_verify() for WRITE SAME

[Sagi Grimberg <sagig@dev.mellanox.co.il>]

On 4/25/2015 5:33 PM, Akinobu Mita wrote:
> For WRITE SAME, data transfer memory only contains a single block but
> protection information is required for all blocks that are written by
> the command.
>
> This makes sbc_dif_generate() and sbc_dif_verify() work for WRITE_SAME.

This feels a bit like an overshoot...

You only have 1 block, is it really a good idea to calculate
the CRC over and over for write same? Wouldn't it be better to
have a really simple sbc_dif_generate_same() that calculates the
block CRC once and uses it for the entire payload (and watches for
Type 1 to increment the ref-tag)?

>
> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
> Cc: Nicholas Bellinger <nab@linux-iscsi.org>
> Cc: Sagi Grimberg <sagig@mellanox.com>
> Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
> Cc: target-devel@vger.kernel.org
> Cc: linux-scsi@vger.kernel.org
> ---
> * Changes from v2:
> - Handle odd SG mapping correctly instead of giving up
>
>   drivers/target/target_core_sbc.c | 28 ++++++++++++++++++++++++++++
>   1 file changed, 28 insertions(+)
>
> diff --git a/drivers/target/target_core_sbc.c b/drivers/target/target_core_sbc.c
> index 33d2426..10c7cb9 100644
> --- a/drivers/target/target_core_sbc.c
> +++ b/drivers/target/target_core_sbc.c
> @@ -1177,6 +1177,24 @@ err:
>   }
>   EXPORT_SYMBOL(sbc_execute_unmap);
>
> +static bool sbc_is_write_same(struct se_cmd *cmd)
> +{
> +	u16 service_action;
> +
> +	switch (cmd->t_task_cdb[0]) {
> +	case WRITE_SAME:
> +	case WRITE_SAME_16:
> +		return true;
> +	case VARIABLE_LENGTH_CMD:
> +		service_action = get_unaligned_be16(&cmd->t_task_cdb[8]);
> +		if (service_action == WRITE_SAME_32)
> +			return true;
> +		break;
> +	}
> +
> +	return false;
> +}
> +
>   void
>   sbc_dif_generate(struct se_cmd *cmd)
>   {
> @@ -1187,6 +1205,7 @@ sbc_dif_generate(struct se_cmd *cmd)
>   	void *daddr, *paddr;
>   	int i, j, offset = 0;
>   	unsigned int block_size = dev->dev_attrib.block_size;
> +	bool is_write_same = sbc_is_write_same(cmd);
>
>   	for_each_sg(cmd->t_prot_sg, psg, cmd->t_prot_nents, i) {
>   		paddr = kmap_atomic(sg_page(psg)) + psg->offset;
> @@ -1201,6 +1220,8 @@ sbc_dif_generate(struct se_cmd *cmd)
>   				offset -= dsg->length;
>   				kunmap_atomic(daddr);
>   				dsg = sg_next(dsg);
> +				if (!dsg && is_write_same)
> +					dsg = cmd->t_data_sg;
>   				daddr = kmap_atomic(sg_page(dsg)) + dsg->offset;
>   			}
>
> @@ -1211,6 +1232,8 @@ sbc_dif_generate(struct se_cmd *cmd)
>   			if (avail < block_size) {
>   				kunmap_atomic(daddr);
>   				dsg = sg_next(dsg);
> +				if (!dsg && is_write_same)
> +					dsg = cmd->t_data_sg;
>   				daddr = kmap_atomic(sg_page(dsg)) + dsg->offset;
>   				offset = block_size - avail;
>   				crc = crc_t10dif_update(crc, daddr, offset);
> @@ -1336,6 +1359,7 @@ sbc_dif_verify(struct se_cmd *cmd, sector_t start, unsigned int sectors,
>   	sense_reason_t rc;
>   	int dsg_off = 0;
>   	unsigned int block_size = dev->dev_attrib.block_size;
> +	bool is_write_same = sbc_is_write_same(cmd);
>
>   	for (; psg && sector < start + sectors; psg = sg_next(psg)) {
>   		paddr = kmap_atomic(sg_page(psg)) + psg->offset;
> @@ -1351,6 +1375,8 @@ sbc_dif_verify(struct se_cmd *cmd, sector_t start, unsigned int sectors,
>   				dsg_off -= dsg->length;
>   				kunmap_atomic(daddr);
>   				dsg = sg_next(dsg);
> +				if (!dsg && is_write_same)
> +					dsg = cmd->t_data_sg;
>   				daddr = kmap_atomic(sg_page(dsg)) + dsg->offset;
>   			}
>
> @@ -1372,6 +1398,8 @@ sbc_dif_verify(struct se_cmd *cmd, sector_t start, unsigned int sectors,
>   			if (avail < block_size) {
>   				kunmap_atomic(daddr);
>   				dsg = sg_next(dsg);
> +				if (!dsg && is_write_same)
> +					dsg = cmd->t_data_sg;
>   				daddr = kmap_atomic(sg_page(dsg)) + dsg->offset;
>   				dsg_off = block_size - avail;
>   				crc = crc_t10dif_update(crc, daddr, dsg_off);
>