[PATCH v2 2/2] target/rd: Don't pass imcomplete scatterlist entries to sbc_dif_verify_*

[Akinobu Mita <akinobu.mita@gmail.com>]

The scatterlist for protection information which is passed to
sbc_dif_verify_read() or sbc_dif_verify_write() requires that
neighboring scatterlist entries are contiguous or chained so that they
can be iterated by sg_next().

However, the protection information for RD-MCP backends could be located
in the multiple scatterlist arrays when the ramdisk space is too large.
So if the read/write request straddles this boundary, sbc_dif_verify_read()
or sbc_dif_verify_write() can't iterate all scatterlist entries.

This fixes it by allocating temporary scatterlist if it is needed.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Nicholas Bellinger <nab@linux-iscsi.org>
Cc: Sagi Grimberg <sagig@dev.mellanox.co.il>
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
---
* No change from v1

 drivers/target/target_core_rd.c | 39 +++++++++++++++++++++++++++++++++++----
 1 file changed, 35 insertions(+), 4 deletions(-)

diff --git a/drivers/target/target_core_rd.c b/drivers/target/target_core_rd.c
index ac5e8d2..6e25eaa 100644
--- a/drivers/target/target_core_rd.c
+++ b/drivers/target/target_core_rd.c
@@ -390,11 +390,12 @@ static sense_reason_t rd_do_prot_rw(struct se_cmd *cmd, dif_verify dif_verify)
 	struct se_device *se_dev = cmd->se_dev;
 	struct rd_dev *dev = RD_DEV(se_dev);
 	struct rd_dev_sg_table *prot_table;
+	bool need_to_release = false;
 	struct scatterlist *prot_sg;
 	u32 sectors = cmd->data_length / se_dev->dev_attrib.block_size;
-	u32 prot_offset, prot_page;
+	u32 prot_offset, prot_page, prot_npages;
 	u64 tmp;
-	sense_reason_t rc;
+	sense_reason_t rc = TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
 
 	tmp = cmd->t_task_lba * se_dev->prot_length;
 	prot_offset = do_div(tmp, PAGE_SIZE);
@@ -404,10 +405,40 @@ static sense_reason_t rd_do_prot_rw(struct se_cmd *cmd, dif_verify dif_verify)
 	if (!prot_table)
 		return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
 
-	prot_sg = &prot_table->sg_table[prot_page -
-					prot_table->page_start_offset];
+	prot_npages = DIV_ROUND_UP(prot_offset + sectors * se_dev->prot_length,
+				   PAGE_SIZE);
+
+	/* prot pages straddles multiple scatterlist tables */
+	if (prot_table->page_end_offset < prot_page + prot_npages - 1) {
+		int i;
+
+		prot_sg = kcalloc(prot_npages, sizeof(*prot_sg), GFP_KERNEL);
+		if (!prot_sg)
+			return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
+
+		need_to_release = true;
+		sg_init_table(prot_sg, prot_npages);
+
+		for (i = 0; i < prot_npages; i++) {
+			if (prot_page + i > prot_table->page_end_offset) {
+				prot_table = rd_get_prot_table(dev,
+								prot_page + i);
+				if (!prot_table)
+					goto out;
+				sg_unmark_end(&prot_sg[i - 1]);
+			}
+			prot_sg[i] = prot_table->sg_table[prot_page + i -
+						prot_table->page_start_offset];
+		}
+	} else {
+		prot_sg = &prot_table->sg_table[prot_page -
+						prot_table->page_start_offset];
+	}
 
 	rc = dif_verify(cmd, cmd->t_task_lba, sectors, 0, prot_sg, prot_offset);
+out:
+	if (need_to_release)
+		kfree(prot_sg);
 
 	return rc;
 }
-- 
1.9.1