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Date: Tue, 27 Jan 2015 22:35:57 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Javi Merino <javi.merino@....com>
Cc: linux-kernel@...r.kernel.org, Dave Martin <Dave.Martin@....com>,
Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v4 1/3] tracing: Add array printing helpers
On Mon, 26 Jan 2015 12:11:49 +0000
Javi Merino <javi.merino@....com> wrote:
> From: Dave Martin <Dave.Martin@....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.
>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Signed-off-by: Dave Martin <Dave.Martin@....com>
> Signed-off-by: Javi Merino <javi.merino@....com>
> ---
> include/linux/ftrace_event.h | 4 ++++
> include/trace/ftrace.h | 9 +++++++++
> kernel/trace/trace_output.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 57 insertions(+)
>
> diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
> index 0bebb5c348b8..5aa4a9269547 100644
> --- a/include/linux/ftrace_event.h
> +++ b/include/linux/ftrace_event.h
> @@ -44,6 +44,10 @@ 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_array_seq(struct trace_seq *p,
> + const void *buf, int buf_len,
> + size_t el_size);
> +
> struct trace_iterator;
> struct trace_event;
>
> diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
> index 139b5067345b..36afd0ed3458 100644
> --- a/include/trace/ftrace.h
> +++ b/include/trace/ftrace.h
> @@ -263,6 +263,14 @@
> #undef __print_hex
> #define __print_hex(buf, buf_len) ftrace_print_hex_seq(p, buf, buf_len)
>
> +#undef __print_array
> +#define __print_array(array, count, el_size) \
> + ({ \
> + BUILD_BUG_ON(el_size != 8 && el_size != 16 && \
> + el_size != 32 && el_size != 64); \
I tried testing this patch by writing a print_array myself, and I kept
hitting this BUILD_BUG_ON, and was wondering WTF? Then it dawned on me.
el_size should not be based on bits, it should be based on bytes. I
passed in "sizeof()" which doesn't work with bits.
Please update to "el_size < 1 || el_size > 8".
and adjust the rest accordingly.
Thanks,
-- Steve
> + ftrace_print_array_seq(p, array, count, el_size); \
> + })
> +
> #undef DECLARE_EVENT_CLASS
> #define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print) \
> static notrace enum print_line_t \
> @@ -674,6 +682,7 @@ static inline void ftrace_test_probe_##call(void) \
> #undef __get_dynamic_array_len
> #undef __get_str
> #undef __get_bitmask
> +#undef __print_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 b77b9a697619..c06bd6e4ae0e 100644
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -177,6 +177,50 @@ ftrace_print_hex_seq(struct trace_seq *p, const unsigned char *buf, int buf_len)
> }
> EXPORT_SYMBOL(ftrace_print_hex_seq);
>
> +const char *
> +ftrace_print_array_seq(struct trace_seq *p, const void *buf, int buf_len,
> + size_t el_size)
> +{
> + const char *ret = trace_seq_buffer_ptr(p);
> + const char *prefix = "";
> + void *ptr = (void *)buf;
> +
> + trace_seq_putc(p, '{');
> +
> + while (ptr < buf + buf_len) {
> + switch (el_size) {
> + case 8:
> + trace_seq_printf(p, "%s0x%x", prefix,
> + *(u8 *)ptr);
> + break;
> + case 16:
> + trace_seq_printf(p, "%s0x%x", prefix,
> + *(u16 *)ptr);
> + break;
> + case 32:
> + trace_seq_printf(p, "%s0x%x", prefix,
> + *(u32 *)ptr);
> + break;
> + case 64:
> + trace_seq_printf(p, "%s0x%llx", prefix,
> + *(u64 *)ptr);
> + break;
> + default:
> + trace_seq_printf(p, "BAD SIZE:%zu 0x%x", el_size,
> + *(u8 *)ptr);
> + el_size = 8;
> + }
> + prefix = ",";
> + ptr += el_size / 8;
> + }
> +
> + trace_seq_putc(p, '}');
> + trace_seq_putc(p, 0);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL(ftrace_print_array_seq);
> +
> int ftrace_raw_output_prep(struct trace_iterator *iter,
> struct trace_event *trace_event)
> {
--
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