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SubjectRe: [PATCH 1/2 v3] tracing/events: provide string with undefined size support



On Tue, 21 Apr 2009, Steven Rostedt wrote:

>
> 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@gmail.com>
> > Cc: Steven Rostedt <rostedt@goodmis.org>
> > Cc: Li Zefan <lizf@cn.fujitsu.com>
> > Cc: Peter Zijlstra <a.p.zijlstra@chello.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@goodmis.org>

Actually I looked at this code deeper than an Ack.

Reviewed-by: Steven Rostedt <rostedt@goodmis.org>

-- Steve



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