lttng_event_expr_event_payload_field_create(field_name) :
lttng_event_expr_channel_context_field_create(field_name);
if (!event_expr) {
ERR("Failed to create %s event expression: field name = `%s`.",
lttng_event_expr_event_payload_field_create(field_name) :
lttng_event_expr_channel_context_field_create(field_name);
if (!event_expr) {
ERR("Failed to create %s event expression: field name = `%s`.",