target: Add internal WRITE_STRIP support

This patch adds WRITE_STRIP support in target_write_prot_action() that
invokes sbc_dif_verify_write() for checking T10-PI metadata before
submitting the I/O to a backend driver.

Upon verify failure, the specific sense code is propigated up the
failure path up to transport_generic_request_failure().

Also, update sbc_dif_verify_write() to only perform the subsequent
protection metadata copy when a valid *sg is passed.

(Use ilog2 instead of division and unlikely for pi_err - Sagi)
Reviewed-by: Martin Petersen <martin.petersen@oracle.com>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_sbc.c

@@ -1342,6 +1342,9 @@ sbc_dif_verify_write(struct se_cmd *cmd, sector_t start, unsigned int sectors,
 		kunmap_atomic(paddr);
 		kunmap_atomic(daddr);
 	}
+	if (!sg)
+		return 0;
+
 	sbc_dif_copy_prot(cmd, sectors, false, sg, sg_off);
 
 	return 0;

drivers/target/target_core_transport.c

@@ -1740,6 +1740,7 @@ void __target_execute_cmd(struct se_cmd *cmd)
 
 static int target_write_prot_action(struct se_cmd *cmd)
 {
+	u32 sectors;
 	/*
 	 * Perform WRITE_INSERT of PI using software emulation when backend
 	 * device has PI enabled, if the transport has not already generated
@@ -1750,6 +1751,21 @@ static int target_write_prot_action(struct se_cmd *cmd)
 		if (!(cmd->se_sess->sup_prot_ops & TARGET_PROT_DOUT_INSERT))
 			sbc_dif_generate(cmd);
 		break;
+	case TARGET_PROT_DOUT_STRIP:
+		if (cmd->se_sess->sup_prot_ops & TARGET_PROT_DOUT_STRIP)
+			break;
+
+		sectors = cmd->data_length >> ilog2(cmd->se_dev->dev_attrib.block_size);
+		cmd->pi_err = sbc_dif_verify_write(cmd, cmd->t_task_lba,
+						   sectors, 0, NULL, 0);
+		if (unlikely(cmd->pi_err)) {
+			spin_lock_irq(&cmd->t_state_lock);
+			cmd->transport_state &= ~CMD_T_BUSY|CMD_T_SENT;
+			spin_unlock_irq(&cmd->t_state_lock);
+			transport_generic_request_failure(cmd, cmd->pi_err);
+			return -1;
+		}
+		break;
 	default:
 		break;
 	}