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

["Nicholas A. Bellinger" <nab@linux-iscsi.org>]

On Thu, 2014-01-09 at 12:32 +0200, Sagi Grimberg wrote:
> 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.

So IBLOCK + PSCSI backends will need to be a non interleaved protection
PASS for fast path operation, and backend protection emulation is
reserved for RAMDISK and perhaps a special FILEIO full emulation mode.

>  I assume that if backstore DIF verify is offloaded as well it does not 
> really matter.

That is my assumption of well..

--nab