Messages in this thread | | | Date | Thu, 10 Jul 2014 11:40:10 -0400 | From | Steven Rostedt <> | Subject | Re: [RFC PATCH v5 01/10] tracing: Add array printing helpers |
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On Thu, 10 Jul 2014 15:18:39 +0100 "Javi Merino" <javi.merino@arm.com> wrote:
> From: Dave Martin <Dave.Martin@arm.com> > > If a trace event contains an array, there is currently no standard > way to format this for text output. Drivers are currently hacking > around this by a) local hacks that use the trace_seq functionailty > directly, or b) just not printing that information. For fixed size > arrays, formatting of the elements can be open-coded, but this gets > cumbersome for arrays of non-trivial size. > > These approaches result in non-standard content of the event format > description delivered to userspace, so userland tools needs to be > taught to understand and parse each array printing method > individually. > > This patch implements common __print_<type>_array() helpers that > tracepoint implementations can use instead of reinventing them. A > simple C-style syntax is used to delimit the array and its elements > {like,this}. > > So that the helpers can be used with large static arrays as well as > dynamic arrays, they take a pointer and element count: they can be > used with __get_dynamic_array() for use with dynamic arrays.
Note, please base any patches like this on my for-next branch, because I have moved the trace_seq code out of trace_print.c. Although, I need to analyze this a little bit more to see if these still belong in trace_print.c or if they should go into trace_seq.c.
My repo is at:
git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Ingo Molnar <mingo@redhat.com> > Signed-off-by: Dave Martin <Dave.Martin@arm.com> > --- > include/linux/ftrace_event.h | 9 ++++++++ > include/trace/ftrace.h | 17 ++++++++++++++ > kernel/trace/trace_output.c | 55 ++++++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 81 insertions(+) > > diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h > index cff3106ffe2c..919f21a3420b 100644 > --- a/include/linux/ftrace_event.h > +++ b/include/linux/ftrace_event.h > @@ -44,6 +44,15 @@ const char *ftrace_print_bitmask_seq(struct trace_seq *p, void *bitmask_ptr, > const char *ftrace_print_hex_seq(struct trace_seq *p, > const unsigned char *buf, int len); > > +const char *ftrace_print_u8_array_seq(struct trace_seq *p, > + const u8 *buf, int count); > +const char *ftrace_print_u16_array_seq(struct trace_seq *p, > + const u16 *buf, int count); > +const char *ftrace_print_u32_array_seq(struct trace_seq *p, > + const u32 *buf, int count); > +const char *ftrace_print_u64_array_seq(struct trace_seq *p, > + const u64 *buf, int count); > + > struct trace_iterator; > struct trace_event; > > diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h > index 26b4f2e13275..15bc5d417aea 100644 > --- a/include/trace/ftrace.h > +++ b/include/trace/ftrace.h > @@ -263,6 +263,19 @@ > #undef __print_hex > #define __print_hex(buf, buf_len) ftrace_print_hex_seq(p, buf, buf_len) > > +#undef __print_u8_array > +#define __print_u8_array(array, count) \ > + ftrace_print_u8_array_seq(p, array, count) > +#undef __print_u16_array > +#define __print_u16_array(array, count) \ > + ftrace_print_u16_array_seq(p, array, count) > +#undef __print_u32_array > +#define __print_u32_array(array, count) \ > + ftrace_print_u32_array_seq(p, array, count) > +#undef __print_u64_array > +#define __print_u64_array(array, count) \ > + ftrace_print_u64_array_seq(p, array, count)
print_hex_seq() is still in trace_output.c, so perhaps it is fine to keep these there too.
> + > #undef DECLARE_EVENT_CLASS > #define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print) \ > static notrace enum print_line_t \ > @@ -676,6 +689,10 @@ static inline void ftrace_test_probe_##call(void) \ > #undef __get_dynamic_array_len > #undef __get_str > #undef __get_bitmask > +#undef __print_u8_array > +#undef __print_u16_array > +#undef __print_u32_array > +#undef __print_u64_array > > #undef TP_printk > #define TP_printk(fmt, args...) "\"" fmt "\", " __stringify(args) > diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c > index f3dad80c20b2..b46238e75523 100644 > --- a/kernel/trace/trace_output.c > +++ b/kernel/trace/trace_output.c > @@ -454,6 +454,61 @@ ftrace_print_hex_seq(struct trace_seq *p, const unsigned char *buf, int buf_len) > } > EXPORT_SYMBOL(ftrace_print_hex_seq); > > +static const char * > +ftrace_print_array_seq(struct trace_seq *p, const void *buf, int buf_len, > + bool (*iterator)(struct trace_seq *p, const char *prefix, > + const void **buf, int *buf_len)) > +{ > + const char *ret = p->buffer + p->len;
There is now a helper in my for-next branch that removes the above open coded code:
const char *ret = trace_seq_buffer_ptr(p);
> + const char *prefix = ""; > + > + trace_seq_putc(p, '{'); > + > + if (iterator(p, prefix, &buf, &buf_len)) { > + prefix = ","; > + > + while (iterator(p, prefix, &buf, &buf_len))
The above doesn't even need the prefix variable. But I would keep it and remove the if and have this:
while (iterator(p, prefix, &buf, &buf_len)) prefix = ",";
and hope gcc just optimizes it. This is not a critical path, don't micro optimize it and make the code more complex than need be, especially when gcc should be smart enough to optimize it for you.
> + ; > + } > + > + trace_seq_putc(p, '}'); > + trace_seq_putc(p, 0);
trace_seq is only one page in size, which should be enough. I'm wondering if we should check the return status of all the trace_seq() calls and return an error.
> + > + return ret; > +} > + > +#define DEFINE_PRINT_ARRAY(type, printk_type, format) \ > +static bool \ > +ftrace_print_array_iterator_##type(struct trace_seq *p, const char *prefix, \ > + const void **buf, int *buf_len) \ > +{ \ > + const type *__src = *buf; \ > + \ > + if (*buf_len < sizeof(*__src)) \ > + return false; \ > + \ > + trace_seq_printf(p, "%s" format, prefix, (printk_type)*__src++); \ > + \ > + *buf = __src; \ > + *buf_len -= sizeof(*__src); \ > + \ > + return true; \ > +} \ > + \ > +const char *ftrace_print_##type##_array_seq( \ > + struct trace_seq *p, const type *buf, int count) \ > +{ \ > + return ftrace_print_array_seq(p, buf, (count) * sizeof(type), \ > + ftrace_print_array_iterator_##type); \ > +} \ > + \ > +EXPORT_SYMBOL(ftrace_print_##type##_array_seq); > + > +DEFINE_PRINT_ARRAY(u8, unsigned int, "0x%x")
Why not "unsigned char"?
> +DEFINE_PRINT_ARRAY(u16, unsigned int, "0x%x")
Why not "unsigned short"?
> +DEFINE_PRINT_ARRAY(u32, unsigned int, "0x%x") > +DEFINE_PRINT_ARRAY(u64, unsigned long long, "0x%llx") > + > int ftrace_raw_output_prep(struct trace_iterator *iter, > struct trace_event *trace_event) > {
-- Steve
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