Hi Steve,
On 7/24/2018 4:30 PM, Steven Rostedt wrote:
On Tue, 24 Jul 2018 16:49:59 -0400 Steven Rostedt rostedt@goodmis.org 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