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SubjectRe: [PATCH v5 24/37] tracing: Add support for 'synthetic' events
On Thu, Nov 09, 2017 at 02:33:55PM -0600, Tom Zanussi wrote:
> Synthetic events are user-defined events generated from hist trigger
> variables saved from one or more other events.
>
> To define a synthetic event, the user writes a simple specification
> consisting of the name of the new event along with one or more
> variables and their type(s), to the tracing/synthetic_events file.
>
> For instance, the following creates a new event named 'wakeup_latency'
> with 3 fields: lat, pid, and prio:
>
> # echo 'wakeup_latency u64 lat; pid_t pid; int prio' >> \
> /sys/kernel/debug/tracing/synthetic_events
>
> Reading the tracing/synthetic_events file lists all the
> currently-defined synthetic events, in this case the event we defined
> above:
>
> # cat /sys/kernel/debug/tracing/synthetic_events
> wakeup_latency u64 lat; pid_t pid; int prio
>
> At this point, the synthetic event is ready to use, and a histogram
> can be defined using it:
>
> # echo 'hist:keys=pid,prio,lat.log2:sort=pid,lat' >> \
> /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
>
> The new event is created under the tracing/events/synthetic/ directory
> and looks and behaves just like any other event:
>
> # ls /sys/kernel/debug/tracing/events/synthetic/wakeup_latency
> enable filter format hist id trigger
>
> Although a histogram can be defined for it, nothing will happen until
> an action tracing that event via the trace_synth() function occurs.
> The trace_synth() function is very similar to all the other trace_*
> invocations spread throughout the kernel, except in this case the
> trace_ function and its corresponding tracepoint isn't statically
> generated but defined by the user at run-time.
>
> How this can be automatically hooked up via a hist trigger 'action' is
> discussed in a subsequent patch.
>
> Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
> ---
> kernel/trace/trace_events_hist.c | 908 ++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 906 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 3504aa8..510b10d 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -20,10 +20,16 @@
> #include <linux/slab.h>
> #include <linux/stacktrace.h>
> #include <linux/rculist.h>
> +#include <linux/tracefs.h>
>
> #include "tracing_map.h"
> #include "trace.h"
>
> +#define SYNTH_SYSTEM "synthetic"
> +#define SYNTH_FIELDS_MAX 16
> +
> +#define STR_VAR_LEN_MAX 32 /* must be multiple of sizeof(u64) */
> +
> struct hist_field;
>
> typedef u64 (*hist_field_fn_t) (struct hist_field *field,
> @@ -270,6 +276,26 @@ struct hist_trigger_data {
> unsigned int n_actions;
> };
>
> +struct synth_field {
> + char *type;
> + char *name;
> + size_t size;
> + bool is_signed;
> + bool is_string;
> +};
> +
> +struct synth_event {
> + struct list_head list;
> + int ref;
> + char *name;
> + struct synth_field **fields;
> + unsigned int n_fields;
> + unsigned int n_u64;
> + struct trace_event_class class;
> + struct trace_event_call call;
> + struct tracepoint *tp;
> +};
> +
> struct action_data;
>
> typedef void (*action_fn_t) (struct hist_trigger_data *hist_data,
> @@ -282,6 +308,803 @@ struct action_data {
> unsigned int var_ref_idx;
> };
>
> +static LIST_HEAD(synth_event_list);
> +static DEFINE_MUTEX(synth_event_mutex);
> +
> +struct synth_trace_event {
> + struct trace_entry ent;
> + u64 fields[];
> +};
> +
> +static int synth_event_define_fields(struct trace_event_call *call)
> +{
> + struct synth_trace_event trace;
> + int offset = offsetof(typeof(trace), fields);
> + struct synth_event *event = call->data;
> + unsigned int i, size, n_u64;
> + char *name, *type;
> + bool is_signed;
> + int ret = 0;
> +
> + for (i = 0, n_u64 = 0; i < event->n_fields; i++) {
> + size = event->fields[i]->size;
> + is_signed = event->fields[i]->is_signed;
> + type = event->fields[i]->type;
> + name = event->fields[i]->name;
> + ret = trace_define_field(call, type, name, offset, size,
> + is_signed, FILTER_OTHER);
> + if (ret)
> + break;
> +
> + if (event->fields[i]->is_string) {
> + offset += STR_VAR_LEN_MAX;
> + n_u64 += STR_VAR_LEN_MAX / sizeof(u64);

Did you use fixed size array for strings?


> + } else {
> + offset += sizeof(u64);
> + n_u64++;
> + }
> + }
> +
> + event->n_u64 = n_u64;
> +
> + return ret;
> +}
> +
> +static bool synth_field_signed(char *type)
> +{
> + if (strncmp(type, "u", 1) == 0)
> + return false;
> +
> + return true;
> +}
> +
> +static int synth_field_is_string(char *type)
> +{
> + if (strstr(type, "char[") != NULL)
> + return true;
> +
> + return false;
> +}
> +
> +static int synth_field_string_size(char *type)
> +{
> + char buf[4], *end, *start;
> + unsigned int len;
> + int size, err;
> +
> + start = strstr(type, "char[");
> + if (start == NULL)
> + return -EINVAL;
> + start += strlen("char[");
> +
> + end = strchr(type, ']');
> + if (!end || end < start)
> + return -EINVAL;
> +
> + len = end - start;
> + if (len > 3)
> + return -EINVAL;
> +
> + strncpy(buf, start, len);
> + buf[len] = '\0';
> +
> + err = kstrtouint(buf, 0, &size);
> + if (err)
> + return err;
> +
> + if (size > STR_VAR_LEN_MAX)
> + return -EINVAL;
> +
> + return size;
> +}

But this seems to use the actual array size for string..

[SNIP]
> +
> +static notrace void trace_event_raw_event_synth(void *__data,
> + u64 *var_ref_vals,
> + unsigned int var_ref_idx)
> +{
> + struct trace_event_file *trace_file = __data;
> + struct synth_trace_event *entry;
> + struct trace_event_buffer fbuffer;
> + struct synth_event *event;
> + unsigned int i, n_u64;
> + int fields_size = 0;
> +
> + event = trace_file->event_call->data;
> +
> + if (trace_trigger_soft_disabled(trace_file))
> + return;
> +
> + fields_size = event->n_u64 * sizeof(u64);
> +
> + entry = trace_event_buffer_reserve(&fbuffer, trace_file,
> + sizeof(*entry) + fields_size);
> + if (!entry)
> + return;
> +
> + for (i = 0, n_u64 = 0; i < event->n_fields; i++) {
> + if (event->fields[i]->is_string) {
> + char *str_val = (char *)(long)var_ref_vals[var_ref_idx + i];
> + char *str_field = (char *)&entry->fields[n_u64];
> +
> + strncpy(str_field, str_val, STR_VAR_LEN_MAX);
> + n_u64 += STR_VAR_LEN_MAX / sizeof(u64);

Here it uses the fixed size again..

Thanks,
Namhyung


> + } else {
> + entry->fields[i] = var_ref_vals[var_ref_idx + i];
> + n_u64++;
> + }
> + }
> +
> + trace_event_buffer_commit(&fbuffer);
> +}

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