[iscsi] Disambiguate the expected target errors in the login response

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/iscsi.h

 #define ISCSI_STATUS_INITIATOR_ERROR_NOT_FOUND		0x03
 #define ISCSI_STATUS_INITIATOR_ERROR_REMOVED		0x04
 #define ISCSI_STATUS_TARGET_ERROR		0x03
+#define ISCSI_STATUS_TARGET_ERROR_UNAVAILABLE		0x01
+#define ISCSI_STATUS_TARGET_ERROR_NO_RESOURCES		0x02
 
 /**
  * iSCSI SCSI command basic header segment

src/net/tcp/iscsi.c

 	__einfo_error ( EINFO_EINVAL_NO_TARGET_IQN )
 #define EINFO_EINVAL_NO_TARGET_IQN \
 	__einfo_uniqify ( EINFO_EINVAL, 0x04, "No target IQN" )
+#define EIO_TARGET_UNAVAILABLE \
+	__einfo_error ( EINFO_EIO_TARGET_UNAVAILABLE )
+#define EINFO_EIO_TARGET_UNAVAILABLE \
+	__einfo_uniqify ( EINFO_EIO, 0x01, "Target not currently operational" )
+#define EIO_TARGET_NO_RESOURCES \
+	__einfo_error ( EINFO_EIO_TARGET_NO_RESOURCES )
+#define EINFO_EIO_TARGET_NO_RESOURCES \
+	__einfo_uniqify ( EINFO_EIO, 0x02, "Target out of resources" )
 #define ENOTSUP_INITIATOR_STATUS \
 	__einfo_error ( EINFO_ENOTSUP_INITIATOR_STATUS )
 #define EINFO_ENOTSUP_INITIATOR_STATUS \
 	__einfo_error ( EINFO_ENOTSUP_DISCOVERY )
 #define EINFO_ENOTSUP_DISCOVERY \
 	__einfo_uniqify ( EINFO_ENOTSUP, 0x03, "Discovery not supported" )
+#define ENOTSUP_TARGET_STATUS \
+	__einfo_error ( EINFO_ENOTSUP_TARGET_STATUS )
+#define EINFO_ENOTSUP_TARGET_STATUS \
+	__einfo_uniqify ( EINFO_ENOTSUP, 0x04, "Unsupported target status" )
 #define EPERM_INITIATOR_AUTHENTICATION \
 	__einfo_error ( EINFO_EPERM_INITIATOR_AUTHENTICATION )
 #define EINFO_EPERM_INITIATOR_AUTHENTICATION \
 			return -ENOTSUP_INITIATOR_STATUS;
 		}
 	case ISCSI_STATUS_TARGET_ERROR :
-		return -EIO;
+		switch ( status_detail ) {
+		case ISCSI_STATUS_TARGET_ERROR_UNAVAILABLE:
+			return -EIO_TARGET_UNAVAILABLE;
+		case ISCSI_STATUS_TARGET_ERROR_NO_RESOURCES:
+			return -EIO_TARGET_NO_RESOURCES;
+		default:
+			return -ENOTSUP_TARGET_STATUS;
+		}
 	default :
 		return -EINVAL;
 	}