SCSI/libiscsi: Add check_protection callback for transports

iSCSI needs to be at least aware that a task involves protection
information.  In case it does, after the transaction completed libiscsi
will ask the transport to check the protection status of the
transaction.

Unlike transport errors, DIF errors should not prevent successful
completion of the transaction from the transport point of view, but
should be escelated to scsi mid-layer when constructing the scsi
result and sense data.

check_protection routine will return the ascq corresponding to the DIF
error that occured (or 0 if no error happened).

return ascq:
- 0x1: GUARD_CHECK_FAILED
- 0x2: APPTAG_CHECK_FAILED
- 0x3: REFTAG_CHECK_FAILED

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Alex Tabachnik <alext@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/scsi/libiscsi.c

@@ -395,6 +395,10 @@ static int iscsi_prep_scsi_cmd_pdu(struct iscsi_task *task)
 		if (rc)
 			return rc;
 	}
+
+	if (scsi_get_prot_op(sc) != SCSI_PROT_NORMAL)
+		task->protected = true;
+
 	if (sc->sc_data_direction == DMA_TO_DEVICE) {
 		unsigned out_len = scsi_out(sc)->length;
 		struct iscsi_r2t_info *r2t = &task->unsol_r2t;
@@ -823,6 +827,33 @@ static void iscsi_scsi_cmd_rsp(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
 
 	sc->result = (DID_OK << 16) | rhdr->cmd_status;
 
+	if (task->protected) {
+		sector_t sector;
+		u8 ascq;
+
+		/**
+		 * Transports that didn't implement check_protection
+		 * callback but still published T10-PI support to scsi-mid
+		 * deserve this BUG_ON.
+		 **/
+		BUG_ON(!session->tt->check_protection);
+
+		ascq = session->tt->check_protection(task, &sector);
+		if (ascq) {
+			sc->result = DRIVER_SENSE << 24 |
+				     SAM_STAT_CHECK_CONDITION;
+			scsi_build_sense_buffer(1, sc->sense_buffer,
+						ILLEGAL_REQUEST, 0x10, ascq);
+			sc->sense_buffer[7] = 0xc; /* Additional sense length */
+			sc->sense_buffer[8] = 0;   /* Information desc type */
+			sc->sense_buffer[9] = 0xa; /* Additional desc length */
+			sc->sense_buffer[10] = 0x80; /* Validity bit */
+
+			put_unaligned_be64(sector, &sc->sense_buffer[12]);
+			goto out;
+		}
+	}
+
 	if (rhdr->response != ISCSI_STATUS_CMD_COMPLETED) {
 		sc->result = DID_ERROR << 16;
 		goto out;
@@ -1567,6 +1598,7 @@ static inline struct iscsi_task *iscsi_alloc_task(struct iscsi_conn *conn,
 	task->have_checked_conn = false;
 	task->last_timeout = jiffies;
 	task->last_xfer = jiffies;
+	task->protected = false;
 	INIT_LIST_HEAD(&task->running);
 	return task;
 }

include/scsi/libiscsi.h

@@ -133,6 +133,10 @@ struct iscsi_task {
 	unsigned long		last_xfer;
 	unsigned long		last_timeout;
 	bool			have_checked_conn;
+
+	/* T10 protection information */
+	bool			protected;
+
 	/* state set/tested under session->lock */
 	int			state;
 	atomic_t		refcount;

include/scsi/scsi_transport_iscsi.h

@@ -167,6 +167,7 @@ struct iscsi_transport {
 				 struct iscsi_bus_flash_conn *fnode_conn);
 	int (*logout_flashnode_sid) (struct iscsi_cls_session *cls_sess);
 	int (*get_host_stats) (struct Scsi_Host *shost, char *buf, int len);
+	u8 (*check_protection)(struct iscsi_task *task, sector_t *sector);
 };
 
 /*