[RFC PATCH] libtraceevent: Add tep_print_selected_fields()

[RFC PATCH] libtraceevent: Add tep_print_selected_fields()

[Yordan Karadzhov (VMware)]

The new method can print only a subset of the unique data fields of
the trace event. The print format is derived from the parsing tokens
(tep_print_parse objects) of the event. As a byproduct of this change
the existing method tep_print_fields() gets upgraded to use the
formats provided by the tokens.

Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
---
 src/event-parse.c | 87 ++++++++++++++++++++++++++++++++++++++++++-----
 src/event-parse.h |  3 ++
 2 files changed, 81 insertions(+), 9 deletions(-)

diff --git a/src/event-parse.c b/src/event-parse.c
index f42ae38..7302f3d 100644
--- a/src/event-parse.c
+++ b/src/event-parse.c
@@ -3585,6 +3585,8 @@ tep_find_field(struct tep_event *event, const char *name)
 	return format;
 }
 
+
+
 /**
  * tep_find_any_field - find any field by name
  * @event: handle for the event
@@ -5333,6 +5335,19 @@ static int is_printable_array(char *p, unsigned int len)
 	return 1;
 }
 
+static void dynamic_offset(struct tep_handle *tep,
+			   struct tep_format_field *field,
+			   void *data,
+			   unsigned int *offset,
+			   unsigned int *len)
+{
+	unsigned long long val;
+
+	val = tep_read_number(tep, data + field->offset, field->size);
+	*offset = val & SHRT_MAX;
+	*len = val >> 16;
+}
+
 void tep_print_field(struct trace_seq *s, void *data,
 		     struct tep_format_field *field)
 {
@@ -5343,12 +5358,9 @@ void tep_print_field(struct trace_seq *s, void *data,
 	if (field->flags & TEP_FIELD_IS_ARRAY) {
 		offset = field->offset;
 		len = field->size;
-		if (field->flags & TEP_FIELD_IS_DYNAMIC) {
-			val = tep_read_number(tep, data + offset, len);
-			offset = val;
-			len = offset >> 16;
-			offset &= 0xffff;
-		}
+		if (field->flags & TEP_FIELD_IS_DYNAMIC)
+			dynamic_offset(tep, field, data, &offset, &len);
+
 		if (field->flags & TEP_FIELD_IS_STRING &&
 		    is_printable_array(data + offset, len)) {
 			trace_seq_printf(s, "%s", (char *)data + offset);
@@ -5398,19 +5410,76 @@ void tep_print_field(struct trace_seq *s, void *data,
 	}
 }
 
-void tep_print_fields(struct trace_seq *s, void *data,
-		      int size __maybe_unused, struct tep_event *event)
+static struct tep_print_parse *parse_format_next(struct tep_print_parse *parse)
+{
+	while (parse) {
+		if (strncmp(parse->format, "%", 1) == 0)
+			break;
+
+		parse = parse->next;
+	}
+
+	return parse;
+}
+
+static void tep_print_fmt_field(struct trace_seq *s, void *data,
+				const char *format,
+				struct tep_format_field *field)
+{
+	struct tep_handle *tep = field->event->tep;
+	unsigned int len, offset;
+	unsigned long long val;
+
+	if (field->flags & TEP_FIELD_IS_DYNAMIC) {
+		dynamic_offset(tep, field, data, &offset, &len);
+		if (len)
+			trace_seq_printf(s, format, (char *)data + offset);
+		else
+			trace_seq_printf(s, format, "(nil)");
+	} else {
+		val = tep_read_number(tep, data + field->offset, field->size);
+		trace_seq_printf(s, format, val);
+	}
+}
+
+void tep_print_selected_fields(struct trace_seq *s, void *data,
+			       struct tep_event *event,
+			       int ignore_mask)
 {
 	struct tep_format_field *field;
+	struct tep_print_parse *parse;
+	unsigned int len;
+	int field_mask = 1;
 
+	parse = event->print_fmt.print_cache;
 	field = event->format.fields;
 	while (field) {
+		parse = parse_format_next(parse);
+
+		if (field_mask & ignore_mask)
+			goto next;
+
 		trace_seq_printf(s, " %s=", field->name);
-		tep_print_field(s, data, field);
+
+		len = strlen(parse->format);
+		if (len > 0 && parse->format[len - 1] == 'x')
+			trace_seq_printf(s, "0x");
+
+		tep_print_fmt_field(s, data, parse->format, field);
+
+ next:
 		field = field->next;
+		parse = parse->next;
+		field_mask *= 2;
 	}
 }
 
+void tep_print_fields(struct trace_seq *s, void *data,
+		      int size __maybe_unused, struct tep_event *event)
+{
+	tep_print_selected_fields(s, data, event, 0);
+}
+
 static int print_function(struct trace_seq *s, const char *format,
 			  void *data, int size, struct tep_event *event,
 			  struct tep_print_arg *arg)
diff --git a/src/event-parse.h b/src/event-parse.h
index d4a876f..fe0fbf4 100644
--- a/src/event-parse.h
+++ b/src/event-parse.h
@@ -547,6 +547,9 @@ void tep_print_field(struct trace_seq *s, void *data,
 		     struct tep_format_field *field);
 void tep_print_fields(struct trace_seq *s, void *data,
 		      int size __maybe_unused, struct tep_event *event);
+void tep_print_selected_fields(struct trace_seq *s, void *data,
+			       struct tep_event *event,
+			       int ignore_mask);
 int tep_strerror(struct tep_handle *tep, enum tep_errno errnum,
 		 char *buf, size_t buflen);
 
-- 
2.30.2

Re: [RFC PATCH] libtraceevent: Add tep_print_selected_fields()

[Yordan Karadzhov]

Steven,

The implementation of static void tep_print_fmt_field() is incomplete.
If you compare the logic there with the implementation of
void tep_print_field() you will see that I am not handling the case of
a field that is an "ARRAY".

Any ideas what is the best way to handle this case?

Thanks!
Yordan


On 2.08.21 г. 14:27, Yordan Karadzhov (VMware) wrote:
> The new method can print only a subset of the unique data fields of
> the trace event. The print format is derived from the parsing tokens
> (tep_print_parse objects) of the event. As a byproduct of this change
> the existing method tep_print_fields() gets upgraded to use the
> formats provided by the tokens.
> 
> Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
> ---
>   src/event-parse.c | 87 ++++++++++++++++++++++++++++++++++++++++++-----
>   src/event-parse.h |  3 ++
>   2 files changed, 81 insertions(+), 9 deletions(-)
> 
> diff --git a/src/event-parse.c b/src/event-parse.c
> index f42ae38..7302f3d 100644
> --- a/src/event-parse.c
> +++ b/src/event-parse.c
> @@ -3585,6 +3585,8 @@ tep_find_field(struct tep_event *event, const char *name)
>   	return format;
>   }
>   
> +
> +
>   /**
>    * tep_find_any_field - find any field by name
>    * @event: handle for the event
> @@ -5333,6 +5335,19 @@ static int is_printable_array(char *p, unsigned int len)
>   	return 1;
>   }
>   
> +static void dynamic_offset(struct tep_handle *tep,
> +			   struct tep_format_field *field,
> +			   void *data,
> +			   unsigned int *offset,
> +			   unsigned int *len)
> +{
> +	unsigned long long val;
> +
> +	val = tep_read_number(tep, data + field->offset, field->size);
> +	*offset = val & SHRT_MAX;
> +	*len = val >> 16;
> +}
> +
>   void tep_print_field(struct trace_seq *s, void *data,
>   		     struct tep_format_field *field)
>   {
> @@ -5343,12 +5358,9 @@ void tep_print_field(struct trace_seq *s, void *data,
>   	if (field->flags & TEP_FIELD_IS_ARRAY) {
>   		offset = field->offset;
>   		len = field->size;
> -		if (field->flags & TEP_FIELD_IS_DYNAMIC) {
> -			val = tep_read_number(tep, data + offset, len);
> -			offset = val;
> -			len = offset >> 16;
> -			offset &= 0xffff;
> -		}
> +		if (field->flags & TEP_FIELD_IS_DYNAMIC)
> +			dynamic_offset(tep, field, data, &offset, &len);
> +
>   		if (field->flags & TEP_FIELD_IS_STRING &&
>   		    is_printable_array(data + offset, len)) {
>   			trace_seq_printf(s, "%s", (char *)data + offset);
> @@ -5398,19 +5410,76 @@ void tep_print_field(struct trace_seq *s, void *data,
>   	}
>   }
>   
> -void tep_print_fields(struct trace_seq *s, void *data,
> -		      int size __maybe_unused, struct tep_event *event)
> +static struct tep_print_parse *parse_format_next(struct tep_print_parse *parse)
> +{
> +	while (parse) {
> +		if (strncmp(parse->format, "%", 1) == 0)
> +			break;
> +
> +		parse = parse->next;
> +	}
> +
> +	return parse;
> +}
> +
> +static void tep_print_fmt_field(struct trace_seq *s, void *data,
> +				const char *format,
> +				struct tep_format_field *field)
> +{
> +	struct tep_handle *tep = field->event->tep;
> +	unsigned int len, offset;
> +	unsigned long long val;
> +
> +	if (field->flags & TEP_FIELD_IS_DYNAMIC) {
> +		dynamic_offset(tep, field, data, &offset, &len);
> +		if (len)
> +			trace_seq_printf(s, format, (char *)data + offset);
> +		else
> +			trace_seq_printf(s, format, "(nil)");
> +	} else {
> +		val = tep_read_number(tep, data + field->offset, field->size);
> +		trace_seq_printf(s, format, val);
> +	}
> +}
> +
> +void tep_print_selected_fields(struct trace_seq *s, void *data,
> +			       struct tep_event *event,
> +			       int ignore_mask)
>   {
>   	struct tep_format_field *field;
> +	struct tep_print_parse *parse;
> +	unsigned int len;
> +	int field_mask = 1;
>   
> +	parse = event->print_fmt.print_cache;
>   	field = event->format.fields;
>   	while (field) {
> +		parse = parse_format_next(parse);
> +
> +		if (field_mask & ignore_mask)
> +			goto next;
> +
>   		trace_seq_printf(s, " %s=", field->name);
> -		tep_print_field(s, data, field);
> +
> +		len = strlen(parse->format);
> +		if (len > 0 && parse->format[len - 1] == 'x')
> +			trace_seq_printf(s, "0x");
> +
> +		tep_print_fmt_field(s, data, parse->format, field);
> +
> + next:
>   		field = field->next;
> +		parse = parse->next;
> +		field_mask *= 2;
>   	}
>   }
>   
> +void tep_print_fields(struct trace_seq *s, void *data,
> +		      int size __maybe_unused, struct tep_event *event)
> +{
> +	tep_print_selected_fields(s, data, event, 0);
> +}
> +
>   static int print_function(struct trace_seq *s, const char *format,
>   			  void *data, int size, struct tep_event *event,
>   			  struct tep_print_arg *arg)
> diff --git a/src/event-parse.h b/src/event-parse.h
> index d4a876f..fe0fbf4 100644
> --- a/src/event-parse.h
> +++ b/src/event-parse.h
> @@ -547,6 +547,9 @@ void tep_print_field(struct trace_seq *s, void *data,
>   		     struct tep_format_field *field);
>   void tep_print_fields(struct trace_seq *s, void *data,
>   		      int size __maybe_unused, struct tep_event *event);
> +void tep_print_selected_fields(struct trace_seq *s, void *data,
> +			       struct tep_event *event,
> +			       int ignore_mask);
>   int tep_strerror(struct tep_handle *tep, enum tep_errno errnum,
>   		 char *buf, size_t buflen);
>   
> 

Re: [RFC PATCH] libtraceevent: Add tep_print_selected_fields()

[Steven Rostedt]

On Mon, 2 Aug 2021 14:39:11 +0300
Yordan Karadzhov <y.karadz@gmail.com> wrote:

> The implementation of static void tep_print_fmt_field() is incomplete.
> If you compare the logic there with the implementation of
> void tep_print_field() you will see that I am not handling the case of
> a field that is an "ARRAY".
> 
> Any ideas what is the best way to handle this case?

I think my reply to your patch should cover this.

-- Steve

Re: [RFC PATCH] libtraceevent: Add tep_print_selected_fields()

[Steven Rostedt]

On Mon,  2 Aug 2021 14:27:14 +0300
"Yordan Karadzhov (VMware)" <y.karadz@gmail.com> wrote:

> The new method can print only a subset of the unique data fields of
> the trace event. The print format is derived from the parsing tokens
> (tep_print_parse objects) of the event. As a byproduct of this change
> the existing method tep_print_fields() gets upgraded to use the
> formats provided by the tokens.

Why add a new API? Just fix tep_print_field().

> 
> Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
> ---
>  src/event-parse.c | 87 ++++++++++++++++++++++++++++++++++++++++++-----
>  src/event-parse.h |  3 ++
>  2 files changed, 81 insertions(+), 9 deletions(-)
> 
> diff --git a/src/event-parse.c b/src/event-parse.c
> index f42ae38..7302f3d 100644
> --- a/src/event-parse.c
> +++ b/src/event-parse.c
> @@ -3585,6 +3585,8 @@ tep_find_field(struct tep_event *event, const char *name)
>  	return format;
>  }
>  
> +
> +

Spurious newlines?

>  /**
>   * tep_find_any_field - find any field by name
>   * @event: handle for the event
> @@ -5333,6 +5335,19 @@ static int is_printable_array(char *p, unsigned int len)
>  	return 1;
>  }
>  
> +static void dynamic_offset(struct tep_handle *tep,
> +			   struct tep_format_field *field,
> +			   void *data,
> +			   unsigned int *offset,
> +			   unsigned int *len)
> +{
> +	unsigned long long val;
> +
> +	val = tep_read_number(tep, data + field->offset, field->size);
> +	*offset = val & SHRT_MAX;

Don't use SHRT_MAX. Although it is the same, there's no connection
of it being a short number (it only matches by coincidence), and I
don't want to add any assumptions that this is a short. It's 16 bits,
and that's all it is. The fact that a short is also 16 bits is just a
coincidence ;-)

> +	*len = val >> 16;

If anything, we should define:

#define TEP_OFFSET_MASK		0xffff
#define TEP_LEN_SHIFT		16

and then we can:

	*offset = val & TEP_OFFSET_MASK;
	*len = val >> TEP_LEN_SHIFT;

Which would make it much easier to read and document what it actually
is.

> +}
> +

Also, the above should be in a separate cleanup patch that that should
remove all the open coded conversions.

>  void tep_print_field(struct trace_seq *s, void *data,
>  		     struct tep_format_field *field)
>  {
> @@ -5343,12 +5358,9 @@ void tep_print_field(struct trace_seq *s, void *data,
>  	if (field->flags & TEP_FIELD_IS_ARRAY) {
>  		offset = field->offset;
>  		len = field->size;
> -		if (field->flags & TEP_FIELD_IS_DYNAMIC) {
> -			val = tep_read_number(tep, data + offset, len);
> -			offset = val;
> -			len = offset >> 16;
> -			offset &= 0xffff;
> -		}
> +		if (field->flags & TEP_FIELD_IS_DYNAMIC)
> +			dynamic_offset(tep, field, data, &offset, &len);
> +
>  		if (field->flags & TEP_FIELD_IS_STRING &&
>  		    is_printable_array(data + offset, len)) {
>  			trace_seq_printf(s, "%s", (char *)data + offset);
> @@ -5398,19 +5410,76 @@ void tep_print_field(struct trace_seq *s, void *data,
>  	}
>  }
>  

What I was talking about is to change tep_print_field() to do something like:

Take the current tep_print_field() and turn it into static _tep_print_field().

 [ Not even compiled tested ]

void tep_print_field(struct trace_seq *s, void *data,
		     struct tep_format_field *field)
{
	struct tep_event = field->event;
	struct tep_print_parse = event->print_fmt.print_cache;
	struct tep_handle *tep = event->tep;
	unsigned int offset, len;

	if (event->flags & TEP_EVENT_FL_FAILED)
		goto out;

	if (field->flags & TEP_FIELD_IS_DYNAMIC)
		dynamic_offset(tep, field, data, &offset, &len);

	for (;parse; parse = parse->next) {
		if (parse->type == PRINT_FMT_STRING)
			continue;
		if (parse->arg->type != TEP_PRINT_FIELD)
			continue;
		if (parse->arg->field.field->field != field)
			continue;

		print_parse_data(parse, s, data, size, event);
		return;
	}

 out:
	/* Not found */
	_tep_print_field(s, data, field);
}

That print_parse_data() would be extracted from print_event_cache()

static int print_parse_data(struct tep_print_parse *parse, struct trace_seq *s,
			    void *data, int size, struct tep_event *event)
{
	if (parse->len_as_arg)
		len_arg = eval_num_arg(data, size, event, parse->len_as_arg);
	switch (parse->type) {
	case PRINT_FMT_ARG_DIGIT:
		print_arg_number(s, parse->format,
				parse->len_as_arg ? len_arg : -1, data,
				 size, parse->ls, event, parse->arg);
		break;
	case PRINT_FMT_ARG_POINTER:
		print_arg_pointer(s, parse->format,
				  parse->len_as_arg ? len_arg : 1,
				  data, size, event, parse->arg);
		break;
	case PRINT_FMT_ARG_STRING:
		print_arg_string(s, parse->format,
				 parse->len_as_arg ? len_arg : -1,
				 data, size, event, parse->arg);
		break;
	case PRINT_FMT_STRING:
	default:
		trace_seq_printf(s, "%s", parse->format);
		/* Return 1 on non field */
		return 1;
	}
	/* Return 0 on field being processed */
	return 0;
}


static void print_event_cache(struct tep_print_parse *parse, struct trace_seq *s,
			      void *data, int size, struct tep_event *event)
{
	int len_arg;

	while (parse) {
		parse = parse->next;
		parse_parse_data(parse, s, data, size, event);
	}
}


> -void tep_print_fields(struct trace_seq *s, void *data,
> -		      int size __maybe_unused, struct tep_event *event)
> +static struct tep_print_parse *parse_format_next(struct tep_print_parse *parse)
> +{
> +	while (parse) {
> +		if (strncmp(parse->format, "%", 1) == 0)
> +			break;
> +
> +		parse = parse->next;
> +	}
> +
> +	return parse;
> +}
> +
> +static void tep_print_fmt_field(struct trace_seq *s, void *data,
> +				const char *format,
> +				struct tep_format_field *field)
> +{
> +	struct tep_handle *tep = field->event->tep;
> +	unsigned int len, offset;
> +	unsigned long long val;
> +
> +	if (field->flags & TEP_FIELD_IS_DYNAMIC) {
> +		dynamic_offset(tep, field, data, &offset, &len);
> +		if (len)
> +			trace_seq_printf(s, format, (char *)data + offset);
> +		else
> +			trace_seq_printf(s, format, "(nil)");
> +	} else {
> +		val = tep_read_number(tep, data + field->offset, field->size);
> +		trace_seq_printf(s, format, val);
> +	}
> +}
> +
> +void tep_print_selected_fields(struct trace_seq *s, void *data,
> +			       struct tep_event *event,
> +			       int ignore_mask)
>  {
>  	struct tep_format_field *field;
> +	struct tep_print_parse *parse;
> +	unsigned int len;
> +	int field_mask = 1;
>  
> +	parse = event->print_fmt.print_cache;
>  	field = event->format.fields;
>  	while (field) {
> +		parse = parse_format_next(parse);
> +
> +		if (field_mask & ignore_mask)
> +			goto next;
> +
>  		trace_seq_printf(s, " %s=", field->name);
> -		tep_print_field(s, data, field);
> +
> +		len = strlen(parse->format);
> +		if (len > 0 && parse->format[len - 1] == 'x')
> +			trace_seq_printf(s, "0x");
> +
> +		tep_print_fmt_field(s, data, parse->format, field);
> +
> + next:
>  		field = field->next;
> +		parse = parse->next;
> +		field_mask *= 2;
>  	}
>  }
>  
> +void tep_print_fields(struct trace_seq *s, void *data,
> +		      int size __maybe_unused, struct tep_event *event)
> +{
> +	tep_print_selected_fields(s, data, event, 0);
> +}
> +
>  static int print_function(struct trace_seq *s, const char *format,
>  			  void *data, int size, struct tep_event *event,
>  			  struct tep_print_arg *arg)
> diff --git a/src/event-parse.h b/src/event-parse.h
> index d4a876f..fe0fbf4 100644
> --- a/src/event-parse.h
> +++ b/src/event-parse.h
> @@ -547,6 +547,9 @@ void tep_print_field(struct trace_seq *s, void *data,
>  		     struct tep_format_field *field);
>  void tep_print_fields(struct trace_seq *s, void *data,
>  		      int size __maybe_unused, struct tep_event *event);
> +void tep_print_selected_fields(struct trace_seq *s, void *data,
> +			       struct tep_event *event,
> +			       int ignore_mask);

Again, I'm not so big on the selected fields version. Just call
tep_print_field for each section, as it just adds to the trace_seq()
which was created for this purpose (to avoid having to enter a list).


-- Steve


>  int tep_strerror(struct tep_handle *tep, enum tep_errno errnum,
>  		 char *buf, size_t buflen);
>  

Re: [RFC PATCH] libtraceevent: Add tep_print_selected_fields()

[Yordan Karadzhov]

On 2.08.21 г. 19:29, Steven Rostedt wrote:
> What I was talking about is to change tep_print_field() to do something like:
> 
> Take the current tep_print_field() and turn it into static _tep_print_field().
> 
>   [ Not even compiled tested ]
> 

Hi Steven,

I am not able to make sense from the code below.

> void tep_print_field(struct trace_seq *s, void *data,
> 		     struct tep_format_field *field)
> {
> 	struct tep_event = field->event;
> 	struct tep_print_parse = event->print_fmt.print_cache;
> 	struct tep_handle *tep = event->tep;
> 	unsigned int offset, len;
> 
> 	if (event->flags & TEP_EVENT_FL_FAILED)
> 		goto out;
> 
> 	if (field->flags & TEP_FIELD_IS_DYNAMIC)
> 		dynamic_offset(tep, field, data, &offset, &len);
> 
> 	for (;parse; parse = parse->next) {

You need
         if (!parse->arg)
			continue;

> 		if (parse->type == PRINT_FMT_STRING)
> 			continue;
> 		if (parse->arg->type != TEP_PRINT_FIELD)
> 			continue;

I can't understand the idea of those two checks. I printed the values and they don't seem to have any selective power.

> 		if (parse->arg->field.field->field != field)
> 			continue;
> 

This does not compile. I guess you mean
  		if (parse->arg->field.field != field)
  			continue;

however "parse->arg->field.field" looks like unused memory (NULL or 0xffffffff) and this check always fails.

Maybe we must call some of the process_XXX()static functions first in order to make your new version of 
tep_print_field() works?

Thanks!
Yordan

> 		print_parse_data(parse, s, data, size, event);
> 		return;
> 	}
> 
>   out:
> 	/* Not found */
> 	

Re: [RFC PATCH] libtraceevent: Add tep_print_selected_fields()

[Steven Rostedt]

On Tue, 3 Aug 2021 15:42:02 +0300
Yordan Karadzhov <y.karadz@gmail.com> wrote:

> On 2.08.21 г. 19:29, Steven Rostedt wrote:
> > What I was talking about is to change tep_print_field() to do something like:
> > 
> > Take the current tep_print_field() and turn it into static _tep_print_field().
> > 
> >   [ Not even compiled tested ]
> >   
> 
> Hi Steven,
> 
> I am not able to make sense from the code below.
> 
> > void tep_print_field(struct trace_seq *s, void *data,
> > 		     struct tep_format_field *field)
> > {
> > 	struct tep_event = field->event;
> > 	struct tep_print_parse = event->print_fmt.print_cache;
> > 	struct tep_handle *tep = event->tep;
> > 	unsigned int offset, len;
> > 
> > 	if (event->flags & TEP_EVENT_FL_FAILED)
> > 		goto out;
> > 
> > 	if (field->flags & TEP_FIELD_IS_DYNAMIC)
> > 		dynamic_offset(tep, field, data, &offset, &len);
> > 
> > 	for (;parse; parse = parse->next) {  
> 
> You need
>          if (!parse->arg)
> 			continue;

Sure. Like I said, I never even compiled this ;-)

> 
> > 		if (parse->type == PRINT_FMT_STRING)
> > 			continue;
> > 		if (parse->arg->type != TEP_PRINT_FIELD)
> > 			continue;  
> 
> I can't understand the idea of those two checks. I printed the values and they don't seem to have any selective power.

Well, the print_cache stores portions of the print fmt format string. Where if you have something like:


  print fmt: "fd: 0x%08lx, offset: 0x%08lx, count: 0x%08lx", ((unsigned long)(REC->fd)), ((unsigned long)(REC->offset)), ((unsigned long)(REC->count))

The "fd: " part is a PRINT_FMT_STRING. We don't want anything to do with that.

But the cache part that has fields, should be an arg of type
TEP_PRINT_FIELD, which should be mapped to some field to print. That
is, one of the REC->fd, REC->offset or REC->count.

That's what you are looking to see how to print it. As it also contains
how that field should be printed normally.


> 
> > 		if (parse->arg->field.field->field != field)
> > 			continue;
> >   
> 
> This does not compile. I guess you mean
>   		if (parse->arg->field.field != field)
>   			continue;
> 
> however "parse->arg->field.field" looks like unused memory (NULL or 0xffffffff) and this check always fails.
> 
> Maybe we must call some of the process_XXX()static functions first in order to make your new version of 
> tep_print_field() works?

How are you calling it? After loading the tep with tracefs_local_events()?

Because it should be loaded via tep_parse_event(), which calll
parse_args() and load the args to the event.

Basically we should be doing what print_event_cache() does, but only
for the field we are interested in.

-- Steve