Target/dif: Introduce protection-passthough-only mode

Some transports (iSCSI/iSER/SRP/FC) support hardware INSERT/STRIP
capabilities while other transports like loopback/vhost-scsi need
perform this is software.

This patch allows fabrics using SCF_PASSTHROUGH_SG_TO_MEM_NOALLOC
to signal the early LUN scan handling case where PROTECT CDB bits
are set, but no fabric buffer has been provided.

For transports which use generic new command these buffers have yet
to be allocated.

Also this way, target may support protection information
against legacy initiators (writes are inserted and reads
are stripped).

(Only set prot_pto for loopback during early special case - nab)

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/loopback/tcm_loop.c

@@ -212,6 +212,10 @@ static void tcm_loop_submission_work(struct work_struct *work)
 		se_cmd->se_cmd_flags |= SCF_BIDI;
 
 	}
+
+	if (!scsi_prot_sg_count(sc) && scsi_get_prot_op(sc) != SCSI_PROT_NORMAL)
+		se_cmd->prot_pto = true;
+
 	rc = target_submit_cmd_map_sgls(se_cmd, tl_nexus->se_sess, sc->cmnd,
 			&tl_cmd->tl_sense_buf[0], tl_cmd->sc->device->lun,
 			scsi_bufflen(sc), tcm_loop_sam_attr(sc),

drivers/target/target_core_sbc.c

@@ -634,7 +634,7 @@ sbc_check_prot(struct se_device *dev, struct se_cmd *cmd, unsigned char *cdb,
 {
 	u8 protect = cdb[1] >> 5;
 
-	if (!cmd->t_prot_sg || !cmd->t_prot_nents)
+	if ((!cmd->t_prot_sg || !cmd->t_prot_nents) && cmd->prot_pto)
 		return true;
 
 	switch (dev->dev_attrib.pi_prot_type) {

drivers/target/target_core_transport.c

@@ -1365,6 +1365,13 @@ int target_submit_cmd_map_sgls(struct se_cmd *se_cmd, struct se_session *se_sess
 		target_put_sess_cmd(se_sess, se_cmd);
 		return 0;
 	}
+
+	rc = target_setup_cmd_from_cdb(se_cmd, cdb);
+	if (rc != 0) {
+		transport_generic_request_failure(se_cmd, rc);
+		return 0;
+	}
+
 	/*
 	 * Save pointers for SGLs containing protection information,
 	 * if present.
@@ -1374,11 +1381,6 @@ int target_submit_cmd_map_sgls(struct se_cmd *se_cmd, struct se_session *se_sess
 		se_cmd->t_prot_nents = sgl_prot_count;
 	}
 
-	rc = target_setup_cmd_from_cdb(se_cmd, cdb);
-	if (rc != 0) {
-		transport_generic_request_failure(se_cmd, rc);
-		return 0;
-	}
 	/*
 	 * When a non zero sgl_count has been passed perform SGL passthrough
 	 * mapping for pre-allocated fabric memory instead of having target

include/target/target_core_base.h

@@ -570,6 +570,7 @@ struct se_cmd {
 	enum target_prot_ho	prot_handover;
 	sense_reason_t		pi_err;
 	sector_t		bad_sector;
+	bool			prot_pto;
 };
 
 struct se_ua {