Hi Steve,
On 7/24/2018 4:30 PM, Steven Rostedt wrote:
On Tue, 24 Jul 2018 16:49:59 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
Hmm it seems we should review the register_trigger() implementation.
It should return the return value of trace_event_trigger_enable_disable(),
shouldn't it?
Yeah, that's not done well. I'll fix it up.
Thanks for pointing it out.
Tom,
register_trigger() is messed up. I should have caught this when it was
first submitted, but I'm totally confused. The comments don't match the
code.
First we have this:
ret = cmd_ops->reg(glob, trigger_ops, trigger_data, file);
/*
* The above returns on success the # of functions enabled,
* but if it didn't find any functions it returns zero.
* Consider no functions a failure too.
*/
Which looks to be total BS.
Yes, it is BS in the case of event triggers. This was taken from the
ftrace function trigger code, where it does make sense. I think I left
it in thinking the code would at some point later converge.
As we have this:
/**
* register_trigger - Generic event_command @reg implementation
* @glob: The raw string used to register the trigger
* @ops: The trigger ops associated with the trigger
* @data: Trigger-specific data to associate with the trigger
* @file: The trace_event_file associated with the event
*
* Common implementation for event trigger registration.
*
* Usually used directly as the @reg method in event command
* implementations.
*
* Return: 0 on success, errno otherwise
And this is how it should work.
*/
static int register_trigger(char *glob, struct event_trigger_ops *ops,
struct event_trigger_data *data,
struct trace_event_file *file)
{
struct event_trigger_data *test;
int ret = 0;
list_for_each_entry_rcu(test, &file->triggers, list) {
if (test->cmd_ops->trigger_type == data->cmd_ops->trigger_type) {
ret = -EEXIST;
goto out;
}
}
if (data->ops->init) {
ret = data->ops->init(data->ops, data);
if (ret < 0)
goto out;
}
list_add_rcu(&data->list, &file->triggers);
ret++;
update_cond_flag(file);
if (trace_event_trigger_enable_disable(file, 1) < 0) {
list_del_rcu(&data->list);
update_cond_flag(file);
ret--;
}
out:
return ret;
}
Where the comment is total wrong. It doesn't return 0 on success, it
returns 1. And if trace_event_trigger_enable_disable() fails it returns
zero.
And that can fail with the call->class->reg() return value, which could
fail for various strange reasons. I don't know why we would want to
return 0 when it fails?
I don't see where ->reg() would return anything but 1 on success. Maybe
I'm missing something. I'll look some more, but I'm thinking of changing
->reg() to return zero on all success, and negative on all errors and
just check those results.
Right, in the case of event triggers, we only register one at a time,
whereas with the trace function triggers, with globbing multiple
functions can register triggers at the same time, so it makes sense
there to have reg() return a count and the more convoluted error handling.
So I agree, simplifying things here by using the standard error handling
would be an improvement.
Tom
-- Steve
