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Message-ID: <alpine.DEB.2.00.0904211749580.10097@gandalf.stny.rr.com>
Date:	Tue, 21 Apr 2009 17:58:50 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>, Zhaolei <zhaolei@...fujitsu.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Li Zefan <lizf@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 1/2 v3] tracing/events: provide string with undefined
 size support


Hi Frederic,

Cool stuff!


On Sun, 19 Apr 2009, Frederic Weisbecker wrote:

> This patch provides the support for dynamic size strings on
> event tracing.
> 
> The key concept is to use a structure with an ending char array field of
> undefined size and use such ability to allocate the minimal size on the
> ring buffer to make one or more string entries fit inside, as opposite
> to a fixed length strings with upper bound.
> 
> The strings themselves are represented using fields which have an offset
> value from the beginning of the entry.
> 
> This patch provides three new macros:
> 
> __string(item, src)
> 
> This one declares a string to the structure inside TP_STRUCT__entry.
> You need to provide the name of the string field and the source that will
> be copied inside.
> This will also add the dynamic size of the string needed for the ring
> buffer entry allocation.
> A stack allocated structure is used to temporarily store the offset
> of each strings, avoiding double calls to strlen() on each event
> insertion.
> 
> __get_str(field)
> 
> This one will give you a pointer to the string you have created. This
> is an abstract helper to resolve the absolute address given the field
> name which is a relative address from the beginning of the trace_structure.
> 
> __assign_str(dst, src)
> 
> Use this macro to automatically perform the string copy from src to
> dst. src must be a variable to assign and dst is the name of a __string
> field.
> 
> Example on how to use it:
> 
> TRACE_EVENT(my_event,
> 	TP_PROTO(char *src1, char *src2),
> 
> 	TP_ARGS(src1, src2),
> 	TP_STRUCT__entry(
> 		__string(str1, src1)
> 		__string(str2, src2)
> 	),
> 	TP_fast_assign(
> 		__assign_str(str1, src1);
> 		__assign_str(str2, src2);
> 	),
> 	TP_printk("%s %s", __get_str(src1), __get_str(src2))
> )
> 
> Of course you can mix-up any __field or __array inside this
> TRACE_EVENT. The position of the __string or __assign_str
> doesn't matter.
> 
> Changes in v2:
> 
> Address the suggestion of Steven Rostedt: drop the opening_string() macro
> and redefine __ending_string() to get the size of the string to be copied
> instead of overwritting the whole ring buffer allocation.
> 
> Changes in v3:
> 
> Address other suggestions of Steven Rostedt and Peter Zijlstra with
> some changes: drop the __ending_string and the need to have only one
> string field.
> Use offsets instead of absolute addresses.
> 
> [ Impact: better usage of memory for string tracing ]
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Li Zefan <lizf@...fujitsu.com>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
>  include/trace/ftrace.h |   88 ++++++++++++++++++++++++++++++++++++++++++++++--
>  1 files changed, 85 insertions(+), 3 deletions(-)
> 
> diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
> index 39a3351..353b7db 100644
> --- a/include/trace/ftrace.h
> +++ b/include/trace/ftrace.h
> @@ -27,6 +27,9 @@
>  #undef __field
>  #define __field(type, item)		type	item;
>  
> +#undef __string
> +#define __string(item, src)		int	__str_loc_##item;
> +
>  #undef TP_STRUCT__entry
>  #define TP_STRUCT__entry(args...) args
>  
> @@ -35,14 +38,53 @@
>  	struct ftrace_raw_##name {				\
>  		struct trace_entry	ent;			\
>  		tstruct						\
> +		char			__str_data[0];		\
>  	};							\
>  	static struct ftrace_event_call event_##name
>  
>  #include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
>  
> +
>  /*
>   * Stage 2 of the trace events.
>   *
> + * Include the following:
> + *
> + * struct ftrace_str_offsets_<call> {
> + *	int				<str1>;
> + *	int				<str2>;
> + *	[...]
> + * };
> + *
> + * The __string() macro will create each int <str>, this is to
> + * keep the offset of each string from the beggining of the event
> + * once we perform the strlen() of the src strings.
> + *
> + */
> +
> +#undef TRACE_FORMAT
> +#define TRACE_FORMAT(call, proto, args, fmt)
> +
> +#undef __array
> +#define __array(type, item, len)
> +
> +#undef __field
> +#define __field(type, item);
> +
> +#undef __string
> +#define __string(item, src)	int item;
> +
> +#undef TRACE_EVENT
> +#define TRACE_EVENT(call, proto, args, tstruct, assign, print)		\
> +	struct ftrace_str_offsets_##call {				\
> +		tstruct;						\
> +	};
> +
> +#include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
> +
> +/*
> + * Stage 3 of the trace events.
> + *
>   * Override the macros in <trace/trace_events.h> to include the following:
>   *
>   * enum print_line_t
> @@ -80,6 +122,9 @@
>  #undef TP_printk
>  #define TP_printk(fmt, args...) fmt "\n", args
>  
> +#undef __get_str
> +#define __get_str(field)	(char *)__entry + __entry->__str_loc_##field

Because __get_str() is used it the "code" part of the macro, we probably 
should put parenthesis around it:

#define __get_str(field)	((char *)__entry + __entry->__str_loc__##field)


> +
>  #undef TRACE_EVENT
>  #define TRACE_EVENT(call, proto, args, tstruct, assign, print)		\
>  enum print_line_t							\
> @@ -146,6 +191,16 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags)	\
>  	if (!ret)							\
>  		return 0;
>  
> +#undef __string
> +#define __string(item, src)						       \
> +	ret = trace_seq_printf(s, "\tfield: __str_loc " #item ";\t"	       \
> +			       "offset:%u;tsize:%u;\n",			       \
> +			       (unsigned int)offsetof(typeof(field),	       \
> +					__str_loc_##item),		       \
> +			       (unsigned int)sizeof(field.__str_loc_##item));  \
> +	if (!ret)							       \
> +		return 0;
> +
>  #undef __entry
>  #define __entry REC
>  
> @@ -189,6 +244,12 @@ ftrace_format_##call(struct trace_seq *s)				\
>  	if (ret)							\
>  		return ret;
>  
> +#undef __string
> +#define __string(item, src)						       \
> +	ret = trace_define_field(event_call, "__str_loc", #item,	       \
> +				offsetof(typeof(field), __str_loc_##item),     \
> +				sizeof(field.__str_loc_##item));
> +
>  #undef TRACE_EVENT
>  #define TRACE_EVENT(call, proto, args, tstruct, func, print)		\
>  int									\
> @@ -212,7 +273,7 @@ ftrace_define_fields_##call(void)					\
>  #include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
>  
>  /*
> - * Stage 3 of the trace events.
> + * Stage 4 of the trace events.
>   *
>   * Override the macros in <trace/trace_events.h> to include the following:
>   *
> @@ -409,6 +470,23 @@ __attribute__((section("_ftrace_events"))) event_##call = {		\
>  #undef __entry
>  #define __entry entry
>  
> +#undef __field
> +#define __field(type, item)
> +
> +#undef __array
> +#define __array(type, item, len)
> +
> +#undef __string
> +#define __string(item, src)						       \
> +	__str_offsets.item = __str_size +				       \
> +			     offsetof(typeof(*entry), __str_data);	       \
> +	__str_size += strlen(src) + 1;
> +
> +#undef __assign_str
> +#define __assign_str(dst, src)						\
> +	__entry->__str_loc_##dst = __str_offsets.dst;			\
> +	strcpy(__get_str(dst), src);
> +
>  #undef TRACE_EVENT
>  #define TRACE_EVENT(call, proto, args, tstruct, assign, print)		\
>  _TRACE_PROFILE(call, PARAMS(proto), PARAMS(args))			\
> @@ -417,18 +495,22 @@ static struct ftrace_event_call event_##call;				\
>  									\
>  static void ftrace_raw_event_##call(proto)				\
>  {									\
> +	struct ftrace_str_offsets_##call __maybe_unused __str_offsets;  \
>  	struct ftrace_event_call *call = &event_##call;			\
>  	struct ring_buffer_event *event;				\
>  	struct ftrace_raw_##call *entry;				\
>  	unsigned long irq_flags;					\
> +	int __str_size = 0;						\
>  	int pc;								\
>  									\
>  	local_save_flags(irq_flags);					\
>  	pc = preempt_count();						\
>  									\
> +	tstruct;							\
> +									\
>  	event = trace_current_buffer_lock_reserve(event_##call.id,	\
> -				  sizeof(struct ftrace_raw_##call),	\
> -				  irq_flags, pc);			\
> +				 sizeof(struct ftrace_raw_##call) + __str_size,\
> +				 irq_flags, pc);			\
>  	if (!event)							\
>  		return;							\
>  	entry	= ring_buffer_event_data(event);			\
> -- 
> 1.6.1

Other than my comment above...

Acked-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve

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