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Date: Mon, 6 Apr 2015 13:54:33 +0900
From: Namhyung Kim <namhyung@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Guilherme Cox <cox@...puter.org>,
Tony Luck <tony.luck@...il.com>,
Xie XiuQi <xiexiuqi@...wei.com>
Subject: Re: [PATCH 07/18 v3] tracing: Add TRACE_DEFINE_ENUM() macro to map
enums to their values
Hi Steve,
On Thu, Apr 02, 2015 at 09:38:09PM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
>
> Several tracepoints use the helper functions __print_symbolic() or
> __print_flags() and pass in enums that do the mapping between the
> binary data stored and the value to print. This works well for reading
> the ASCII trace files, but when the data is read via userspace tools
> such as perf and trace-cmd, the conversion of the binary value to a
> human string format is lost if an enum is used, as userspace does not
> have access to what the ENUM is.
>
> For example, the tracepoint trace_tlb_flush() has:
>
> __print_symbolic(REC->reason,
> { TLB_FLUSH_ON_TASK_SWITCH, "flush on task switch" },
> { TLB_REMOTE_SHOOTDOWN, "remote shootdown" },
> { TLB_LOCAL_SHOOTDOWN, "local shootdown" },
> { TLB_LOCAL_MM_SHOOTDOWN, "local mm shootdown" })
>
> Which maps the enum values to the strings they represent. But perf and
> trace-cmd do no know what value TLB_LOCAL_MM_SHOOTDOWN is, and would
> not be able to map it.
>
> With TRACE_DEFINE_ENUM(), developers can place these in the event header
> files and ftrace will convert the enums to their values:
>
> By adding:
>
> TRACE_DEFINE_ENUM(TLB_FLUSH_ON_TASK_SWITCH);
> TRACE_DEFINE_ENUM(TLB_REMOTE_SHOOTDOWN);
> TRACE_DEFINE_ENUM(TLB_LOCAL_SHOOTDOWN);
> TRACE_DEFINE_ENUM(TLB_LOCAL_MM_SHOOTDOWN);
>
> $ cat /sys/kernel/debug/tracing/events/tlb/tlb_flush/format
> [...]
> __print_symbolic(REC->reason,
> { 0, "flush on task switch" },
> { 1, "remote shootdown" },
> { 2, "local shootdown" },
> { 3, "local mm shootdown" })
>
> The above is what userspace expects to see, and tools do not need to
> be modified to parse them.
>
> Cc: Guilherme Cox <cox@...puter.org>
> Cc: Tony Luck <tony.luck@...il.com>
> Cc: Xie XiuQi <xiexiuqi@...wei.com>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
[SNIP]
> +static void update_event_printk(struct ftrace_event_call *call,
> + struct trace_enum_map *map)
> +{
> + char *ptr;
> + int quote = 0;
> + int len = strlen(map->enum_string);
> +
> + for (ptr = call->print_fmt; *ptr; ptr++) {
> + if (*ptr == '\\') {
> + ptr++;
> + /* paranoid */
> + if (!*ptr)
> + break;
> + continue;
> + }
> + if (*ptr == '"') {
> + quote ^= 1;
> + continue;
> + }
> + if (quote)
> + continue;
> + if (isdigit(*ptr)) {
> + /* skip numbers */
> + do {
> + ptr++;
> + /* Check for alpha chars like ULL */
> + } while (isalnum(*ptr));
> + /*
> + * A number must have some kind of delimiter after
> + * it, and we can ignore that too.
> + */
> + continue;
> + }
> + if (isalpha(*ptr) || *ptr == '_') {
> + if (strncmp(map->enum_string, ptr, len) == 0 &&
> + !isalnum(ptr[len]) && ptr[len] != '_') {
> + ptr = enum_replace(ptr, map, len);
> + /* Hmm, enum string smaller than value */
> + if (WARN_ON_ONCE(!ptr))
> + return;
> + /*
> + * No need to decrement here, as enum_replace()
> + * returns the pointer to the character passed
> + * the enum, and two enums can not be placed
> + * back to back without something in between.
> + * We can skip that something in between.
> + */
> + continue;
Maybe I'm becoming a bit paranoid, what I worried was like this:
ENUM1\"ENUM2\"
In this case, it skips the backslash and makes quotation effective..
> + }
> + skip_more:
> + do {
> + ptr++;
> + } while (isalnum(*ptr) || *ptr == '_');
> + /*
> + * If what comes after this variable is a '.' or
> + * '->' then we can continue to ignore that string.
> + */
> + if (*ptr == '.' || (ptr[0] == '-' && ptr[1] == '>')) {
> + ptr += *ptr == '.' ? 1 : 2;
> + goto skip_more;
> + }
> + /*
> + * Once again, we can skip the delimiter that came
> + * after the string.
> + */
> + continue;
> + }
> + }
> +}
> +
> +void trace_event_enum_update(struct trace_enum_map **map, int len)
> +{
> + struct ftrace_event_call *call, *p;
> + const char *last_system = NULL;
> + int last_i;
> + int i;
> +
> + down_write(&trace_event_sem);
> + list_for_each_entry_safe(call, p, &ftrace_events, list) {
> + /* events are usually grouped together with systems */
> + if (!last_system || call->class->system != last_system) {
I think simply checking "call->class->system != last_system" would work.
Thanks,
Namhyung
> + last_i = 0;
> + last_system = call->class->system;
> + }
> +
> + for (i = last_i; i < len; i++) {
> + if (call->class->system == map[i]->system) {
> + /* Save the first system if need be */
> + if (!last_i)
> + last_i = i;
> + update_event_printk(call, map[i]);
> + }
> + }
> + }
> + up_write(&trace_event_sem);
> +}
> +
> static struct ftrace_event_file *
> trace_create_new_event(struct ftrace_event_call *call,
> struct trace_array *tr)
> --
> 2.1.4
>
>
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