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SubjectRe: [PATCH v5 15/37] tracing: Add variable support to hist triggers
Hi Tom,

On Thu, Nov 09, 2017 at 02:33:46PM -0600, 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 ...
> # 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:...
>
> 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 ...
>
> Variables set as above can be used by being referenced from another
> event, as described in a subsequent patch.
>
> Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
> Signed-off-by: Baohong Liu <baohong.liu@intel.com>
> ---

[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) {
> + kfree(hist_data->attrs->var_defs.name[n_vars]);
> + ret = -ENOMEM;
> + goto free;
> + }
> + 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;

This will silently discard all variables. Why not returning an error?
Also I think it should be moved to the beginning of this block..

Thanks,
Namhyung


> + }
> + }
> +
> + return ret;
> + free:
> + free_var_defs(hist_data);
> +
> + return ret;
> +}

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