tcm_loop: Convert I/O path to use target_submit_cmd_map_sgls

This patch converts tcm_loop to use target_submit_cmd_map_sgls() for
I/O submission and mapping of pre-allocated SGL memory from incoming
scsi_cmnd -> se_cmd descriptors.

This includes removing the original open-coded fabric uses of target
core callers to support transport_generic_map_mem_to_cmd() between
target_setup_cmd_from_cdb() and transport_handle_cdb_direct() logic.

(v2: Use renamed target_submit_cmd_map_sgls)

Reported-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Nicholas Bellinger <[e-mail]>

drivers/target/loopback/tcm_loop.c

···
 	struct tcm_loop_tpg *tl_tpg;
 	struct scatterlist *sgl_bidi = NULL;
 	u32 sgl_bidi_count = 0;
-	int ret;
+	int rc;
 
 	tl_hba = *(struct tcm_loop_hba **)shost_priv(sc->device->host);
 	tl_tpg = &tl_hba->tl_hba_tpgs[sc->device->id];
···
 		set_host_byte(sc, DID_ERROR);
 		goto out_done;
 	}
-
-	transport_init_se_cmd(se_cmd, tl_tpg->tl_se_tpg.se_tpg_tfo,
-			tl_nexus->se_sess,
-			scsi_bufflen(sc), sc->sc_data_direction,
-			tcm_loop_sam_attr(sc), &tl_cmd->tl_sense_buf[0]);
-
 	if (scsi_bidi_cmnd(sc)) {
 		struct scsi_data_buffer *sdb = scsi_in(sc);
 
···
 		se_cmd->se_cmd_flags |= SCF_BIDI;
 
 	}
-
-	if (transport_lookup_cmd_lun(se_cmd, tl_cmd->sc->device->lun) < 0) {
-		kmem_cache_free(tcm_loop_cmd_cache, tl_cmd);
+	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),
+			sc->sc_data_direction, 0,
+			scsi_sglist(sc), scsi_sg_count(sc),
+			sgl_bidi, sgl_bidi_count);
+	if (rc < 0) {
 		set_host_byte(sc, DID_NO_CONNECT);
 		goto out_done;
 	}
-
-	/*
-	 * Because some userspace code via scsi-generic do not memset their
-	 * associated read buffers, go ahead and do that here for type
-	 * non-data CDBs.  Also note that this is currently guaranteed to be a
-	 * single SGL for this case by target core in
-	 * target_setup_cmd_from_cdb() -> transport_generic_cmd_sequencer().
-	 */
-	if (!(se_cmd->se_cmd_flags & SCF_SCSI_DATA_CDB) &&
-	    se_cmd->data_direction == DMA_FROM_DEVICE) {
-		struct scatterlist *sg = scsi_sglist(sc);
-		unsigned char *buf = kmap(sg_page(sg)) + sg->offset;
-
-		if (buf != NULL) {
-			memset(buf, 0, sg->length);
-			kunmap(sg_page(sg));
-		}
-	}
-
-	ret = target_setup_cmd_from_cdb(se_cmd, sc->cmnd);
-	if (ret == -ENOMEM) {
-		transport_send_check_condition_and_sense(se_cmd,
-				TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE, 0);
-		transport_generic_free_cmd(se_cmd, 0);
-		return;
-	} else if (ret < 0) {
-		if (se_cmd->se_cmd_flags & SCF_SCSI_RESERVATION_CONFLICT)
-			tcm_loop_queue_status(se_cmd);
-		else
-			transport_send_check_condition_and_sense(se_cmd,
-					se_cmd->scsi_sense_reason, 0);
-		transport_generic_free_cmd(se_cmd, 0);
-		return;
-	}
-
-	ret = transport_generic_map_mem_to_cmd(se_cmd, scsi_sglist(sc),
-			scsi_sg_count(sc), sgl_bidi, sgl_bidi_count);
-	if (ret) {
-		transport_send_check_condition_and_sense(se_cmd,
-					se_cmd->scsi_sense_reason, 0);
-		transport_generic_free_cmd(se_cmd, 0);
-		return;
-	}
-	transport_handle_cdb_direct(se_cmd);
 	return;
 
 out_done: