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Date: Mon, 9 Oct 2017 12:27:27 +0900
From: Namhyung Kim <namhyung@...nel.org>
To: Tom Zanussi <tom.zanussi@...ux.intel.com>
Cc: rostedt@...dmis.org, tglx@...utronix.de, mhiramat@...nel.org,
vedang.patel@...el.com, bigeasy@...utronix.de,
joel.opensrc@...il.com, joelaf@...gle.com,
mathieu.desnoyers@...icios.com, baohong.liu@...el.com,
rajvi.jingar@...el.com, linux-kernel@...r.kernel.org,
linux-rt-users@...r.kernel.org, kernel-team@....com
Subject: Re: [PATCH v3 12/33] tracing: Add variable support to hist triggers
Hi Tom,
On Fri, Sep 22, 2017 at 02:59:52PM -0500, Tom Zanussi wrote:
> Add support for saving the value of a current event's event field by
> assigning it to a variable that can be read by a subsequent event.
>
> The basic syntax for saving a variable is to simply prefix a unique
> variable name not corresponding to any keyword along with an '=' sign
> to any event field.
>
> Both keys and values can be saved and retrieved in this way:
>
> # echo 'hist:keys=next_pid:vals=$ts0:ts0=common_timestamp ...
The 'common_timestamp' needs a '$' prefix, right?
> # echo 'hist:timer_pid=common_pid:key=$timer_pid ...'
>
> If a variable isn't a key variable or prefixed with 'vals=', the
> associated event field will be saved in a variable but won't be summed
> as a value:
>
> # echo 'hist:keys=next_pid:ts1=common_timestamp:...
Ditto.
>
> Multiple variables can be assigned at the same time:
>
> # echo 'hist:keys=pid:vals=$ts0,$b,field2:ts0=common_timestamp,b=field1 ...
>
> Multiple (or single) variables can also be assigned at the same time
> using separate assignments:
>
> # echo 'hist:keys=pid:vals=$ts0:ts0=common_timestamp:b=field1:c=field2 ...
Same here..
So you separated the variable definition and it should not be a part
of key or value field, right?
>
> Variables set as above can be used by being referenced from another
> event, as described in a subsequent patch.
That means, a variable should be unique (in a tracing instance at least).
>
> Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
> Signed-off-by: Baohong Liu <baohong.liu@...el.com>
> ---
> kernel/trace/trace_events_hist.c | 374 ++++++++++++++++++++++++++++++++++-----
> 1 file changed, 334 insertions(+), 40 deletions(-)
>
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index c2abe41..0d99548 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -30,6 +30,13 @@ typedef u64 (*hist_field_fn_t) (struct hist_field *field, void *event,
> struct ring_buffer_event *rbe);
>
> #define HIST_FIELD_OPERANDS_MAX 2
> +#define HIST_FIELDS_MAX (TRACING_MAP_FIELDS_MAX + TRACING_MAP_VARS_MAX)
> +
> +struct hist_var {
> + char *name;
> + struct hist_trigger_data *hist_data;
> + unsigned int idx;
> +};
>
> struct hist_field {
> struct ftrace_event_field *field;
> @@ -40,6 +47,7 @@ struct hist_field {
> unsigned int is_signed;
> struct hist_field *operands[HIST_FIELD_OPERANDS_MAX];
> struct hist_trigger_data *hist_data;
> + struct hist_var var;
> };
>
> static u64 hist_field_none(struct hist_field *field, void *event,
> @@ -138,6 +146,14 @@ enum hist_field_flags {
> HIST_FIELD_FL_LOG2 = 1 << 9,
> HIST_FIELD_FL_TIMESTAMP = 1 << 10,
> HIST_FIELD_FL_TIMESTAMP_USECS = 1 << 11,
> + HIST_FIELD_FL_VAR = 1 << 12,
> + HIST_FIELD_FL_VAR_ONLY = 1 << 13,
And then I'm not sure what _VAR_ONLY flag is for. IIUC it's used to
identify pure variable definition from a definition in value fields.
But it's not possible anymore, no?
> +};
> +
> +struct var_defs {
> + unsigned int n_vars;
> + char *name[TRACING_MAP_VARS_MAX];
> + char *expr[TRACING_MAP_VARS_MAX];
> };
>
[SNIP]
> +static int create_var_field(struct hist_trigger_data *hist_data,
> + unsigned int val_idx,
> + struct trace_event_file *file,
> + char *var_name, char *expr_str)
> +{
> + unsigned long flags = 0;
> +
> + if (WARN_ON(val_idx >= TRACING_MAP_VALS_MAX + TRACING_MAP_VARS_MAX))
> + return -EINVAL;
> +
> + if (find_var(file, var_name) && !hist_data->remove) {
Is this for the uniqueness check? But I think it only checks
variables in the current event (file).
> + return -EINVAL;
> + }
> +
> + flags |= HIST_FIELD_FL_VAR;
> + hist_data->n_vars++;
> + if (hist_data->n_vars > TRACING_MAP_VARS_MAX) {
> + return -EINVAL;
> + }
> +
> + flags |= HIST_FIELD_FL_VAR_ONLY;
> +
> + return __create_val_field(hist_data, val_idx, file, var_name, expr_str, flags);
> +}
> +
[SNIP]
> +static int parse_var_defs(struct hist_trigger_data *hist_data)
> +{
> + char *s, *str, *var_name, *field_str;
> + unsigned int i, j, n_vars = 0;
> + int ret = 0;
> +
> + for (i = 0; i < hist_data->attrs->n_assignments; i++) {
> + str = hist_data->attrs->assignment_str[i];
> + for (j = 0; j < TRACING_MAP_VARS_MAX; j++) {
> + field_str = strsep(&str, ",");
> + if (!field_str)
> + break;
> +
> + var_name = strsep(&field_str, "=");
> + if (!var_name || !field_str) {
> + ret = -EINVAL;
> + goto free;
> + }
> +
> + s = kstrdup(var_name, GFP_KERNEL);
> + if (!s) {
> + ret = -ENOMEM;
> + goto free;
> + }
> + hist_data->attrs->var_defs.name[n_vars] = s;
> +
> + s = kstrdup(field_str, GFP_KERNEL);
> + if (!s) {
> + ret = -ENOMEM;
> + goto free;
It seems that it might leak the copy of var_name here..
Thanks,
Namhyung
> + }
> + hist_data->attrs->var_defs.expr[n_vars++] = s;
> +
> + hist_data->attrs->var_defs.n_vars = n_vars;
> +
> + if (n_vars == TRACING_MAP_VARS_MAX)
> + goto free;
> + }
> + }
> +
> + return ret;
> + free:
> + free_var_defs(hist_data);
> +
> + return ret;
> +}
> +
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