On Wed, 14 Dec 2022 22:11:42 +0800
Linyu Yuan <quic_linyyuan@xxxxxxxxxxx> wrote:
> there is one dwc3 trace event declare as below,
> DECLARE_EVENT_CLASS(dwc3_log_event,
> TP_PROTO(u32 event, struct dwc3 *dwc),
> TP_ARGS(event, dwc),
> TP_STRUCT__entry(
> __field(u32, event)
> __field(u32, ep0state)
> __dynamic_array(char, str, DWC3_MSG_MAX)
> ),
> TP_fast_assign(
> __entry->event = event;
> __entry->ep0state = dwc->ep0state;
> ),
> TP_printk("event (%08x): %s", __entry->event,
> dwc3_decode_event(__get_str(str), DWC3_MSG_MAX,
> __entry->event, __entry->ep0state))
> );
> the problem is when trace function called, it will allocate up to
> DWC3_MSG_MAX bytes from trace event buffer, but never fill the buffer
> during fast assignment, it only fill the buffer when output function are
> called, so this means if output function are not called, the buffer will
> never used.
>
> add __alloc_buf() and __get_buf() which will not allocate event buffer
> when trace function called, but when trace output function called, it will
> kmalloc buffer with size DWC3_MSG_MAX for temprary usage and free it
> before trace output function return.
This looks exactly like what the trace_seq *p is to be used for.
static notrace enum print_line_t \
trace_raw_output_##call(struct trace_iterator *iter, int flags, \
struct trace_event *trace_event) \
{ \
struct trace_seq *s = &iter->seq; \
struct trace_seq __maybe_unused *p = &iter->tmp_seq; \
^^^^^^^^^^^^^^^^^^^^
struct trace_event_raw_##call *field; \
int ret; \
\
field = (typeof(field))iter->ent; \
\
ret = trace_raw_output_prep(iter, trace_event); \
if (ret != TRACE_TYPE_HANDLED) \
return ret; \
\
trace_event_printf(iter, print); \
\
return trace_handle_return(s); \
} \
That is a trace_seq buffer that is for temporary usage during the output.
See:
include/trace/events/libata.h
include/trace/events/scsi.h
As well as the macros trace_print_bitmask_seq(), trace_print_flags_seq(),
trace_print_symbols_seq(), etc.
-- Steve
