scsi: target: Allows backend drivers to fail with specific sense codes

Currently, backend drivers can fail I/O with SAM_STAT_CHECK_CONDITION which
gets us TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE.

Add a new helper that allows backend drivers to fail with specific sense
codes.

This is based on a patch from Mike Christie <[e-mail]>.

Cc: Mike Christie <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: David Disseldorp <[e-mail]>
Signed-off-by: Sergey Samoylenko <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/target/target_core_transport.c

···
 {
 	struct se_cmd *cmd = container_of(work, struct se_cmd, work);
 
-	transport_generic_request_failure(cmd,
-			TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE);
+	transport_generic_request_failure(cmd, cmd->sense_reason);
 }
 
 /*
···
 }
 
 /* May be called from interrupt context so must not sleep. */
-void target_complete_cmd(struct se_cmd *cmd, u8 scsi_status)
+void target_complete_cmd_with_sense(struct se_cmd *cmd, u8 scsi_status,
+				    sense_reason_t sense_reason)
 {
 	struct se_wwn *wwn = cmd->se_sess->se_tpg->se_tpg_wwn;
 	int success, cpu;
···
 		return;
 
 	cmd->scsi_status = scsi_status;
+	cmd->sense_reason = sense_reason;
 
 	spin_lock_irqsave(&cmd->t_state_lock, flags);
 	switch (cmd->scsi_status) {
···
 		cpu = wwn->cmd_compl_affinity;
 
 	queue_work_on(cpu, target_completion_wq, &cmd->work);
+}
+EXPORT_SYMBOL(target_complete_cmd_with_sense);
+
+void target_complete_cmd(struct se_cmd *cmd, u8 scsi_status)
+{
+	target_complete_cmd_with_sense(cmd, scsi_status, scsi_status ?
+			      TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE :
+			      TCM_NO_SENSE);
 }
 EXPORT_SYMBOL(target_complete_cmd);
 

include/target/target_core_backend.h

···
 
 void	target_complete_cmd(struct se_cmd *, u8);
 void	target_set_cmd_data_length(struct se_cmd *, int);
+void	target_complete_cmd_with_sense(struct se_cmd *, u8, sense_reason_t);
 void	target_complete_cmd_with_length(struct se_cmd *, u8, int);
 
 void	transport_copy_sense_to_cmd(struct se_cmd *, unsigned char *);

include/target/target_core_base.h

···
 #define TCM_ACA_TAG	0x24
 
 struct se_cmd {
+	/* Used for fail with specific sense codes */
+	sense_reason_t		sense_reason;
 	/* SAM response code being sent to initiator */
 	u8			scsi_status;
 	u16			scsi_sense_length;