Re: [RFC][PATCH 06/17 v2] tracing: Add TRACE_DEFINE_ENUM() macro to map enums to their values

Namhyung Kim
2015-04-02T07:54:14Z

Hi Steve,

On Wed, Apr 01, 2015 at 09:56:54PM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.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@computer.org>
> Cc: Tony Luck <tony.luck@gmail.com>
> Cc: Xie XiuQi <xiexiuqi@huawei.com>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

[SNIP]
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index db54dda10ccc..6b7fd0bf5d28 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -1704,6 +1704,102 @@ __register_event(struct ftrace_event_call *call, struct module *mod)
> return 0;
> }
>
> +static char *enum_replace(char *ptr, struct trace_enum_map *map, int len)
> +{
> + int rlen;
> + int elen;
> +
> + /* Find the length of the enum value as a string */
> + elen = snprintf(ptr, 0, "%ld", map->enum_value);
> + /* Make sure there's enough room to replace the string with the value */
> + if (len < elen)
> + return NULL;
> +
> + snprintf(ptr, elen + 1, "%ld", map->enum_value);
> +
> + /* Get the rest of the string of ptr */
> + rlen = strlen(ptr + len);
> + memmove(ptr + elen, ptr + len, rlen);
> + /* Make sure we end the new string */
> + ptr[elen + rlen] = 0;
> +
> + return ptr + elen;
> +}
> +
> +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++;
> + } while (isalnum(*ptr) || *ptr == '_');
> + /* we went one too many */

Hmm.. it looks like to skip variable name after a number. Shouldn't it be

do { ptr++; } while (isdigit(*ptr));

?

> + ptr--;
> + 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;
> + continue;

I guess it also needs to decrease the ptr here.

> + }
> + do {
> + ptr++;
> + } while (isalnum(*ptr) || *ptr == '_');
> + /* we went one too many */
> + ptr--;
> + 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)
> + last_i = 0;

I think it needs to update the last_system here.

Thanks,
Namhyung

> +
> + 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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