scsi: target: core: Add cmd length set before cmd complete

TCM doesn't properly handle underflow case for service actions. One way to
prevent it is to always complete command with
target_complete_cmd_with_length(), however it requires access to data_sg,
which is not always available.

This change introduces target_set_cmd_data_length() function which allows
to set command data length before completing it.

Link: https://lore.kernel.org/r/20210209072202.41154-2-a.miloserdov@yadro.com
Reviewed-by: Roman Bolshakov <r.bolshakov@yadro.com>
Reviewed-by: Bodo Stroesser <bostroesser@gmail.com>
Signed-off-by: Aleksandr Miloserdov <a.miloserdov@yadro.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/target_core_transport.c

@@ -879,11 +879,9 @@ void target_complete_cmd(struct se_cmd *cmd, u8 scsi_status)
 }
 EXPORT_SYMBOL(target_complete_cmd);
 
-void target_complete_cmd_with_length(struct se_cmd *cmd, u8 scsi_status, int length)
+void target_set_cmd_data_length(struct se_cmd *cmd, int length)
 {
-	if ((scsi_status == SAM_STAT_GOOD ||
-	     cmd->se_cmd_flags & SCF_TREAT_READ_AS_NORMAL) &&
-	    length < cmd->data_length) {
+	if (length < cmd->data_length) {
 		if (cmd->se_cmd_flags & SCF_UNDERFLOW_BIT) {
 			cmd->residual_count += cmd->data_length - length;
 		} else {
@@ -893,6 +891,15 @@ void target_complete_cmd_with_length(struct se_cmd *cmd, u8 scsi_status, int len
 
 		cmd->data_length = length;
 	}
+}
+EXPORT_SYMBOL(target_set_cmd_data_length);
+
+void target_complete_cmd_with_length(struct se_cmd *cmd, u8 scsi_status, int length)
+{
+	if (scsi_status == SAM_STAT_GOOD ||
+	    cmd->se_cmd_flags & SCF_TREAT_READ_AS_NORMAL) {
+		target_set_cmd_data_length(cmd, length);
+	}
 
 	target_complete_cmd(cmd, scsi_status);
 }

include/target/target_core_backend.h

@@ -72,6 +72,7 @@ int	transport_backend_register(const struct target_backend_ops *);
 void	target_backend_unregister(const struct target_backend_ops *);
 
 void	target_complete_cmd(struct se_cmd *, u8);
+void	target_set_cmd_data_length(struct se_cmd *, int);
 void	target_complete_cmd_with_length(struct se_cmd *, u8, int);
 
 void	transport_copy_sense_to_cmd(struct se_cmd *, unsigned char *);