Re: [PATCH v3 01/10] cxl: add helper function to parse trace event to json object

[Steven Rostedt <rostedt@goodmis.org>]

On Mon, 14 Nov 2022 12:44:51 -0800
Alison Schofield <alison.schofield@intel.com> wrote:

> Hi Steve,
> 
> I tried to use the uuid_t type in another TRACE event (cxl_poison), and
> ran into the problem mentioned above.
> 
> It seems to be a problem in libtraceevent (or a user error ;))

Correct. When I said trace-cmd, I really meant libtraceevent, but I tend to
blur the two as libtracevenet was born out of trace-cmd.

> 
> When we have:
> 	TP_STRUCT__entry
> 		__field_struct(uuid_t, hdr_uuid)
> 
> 	TP__fast_assign
> 		memcpy(&__entry->hdr.uuid, &(hdr).id, sizeof(uuid_t));
> 
> 	TP_printk("uuid= %pU",  &__entry->hdr.uuid)
> 
> Libtraceevent fails to handle that "&" in "&__entry->hrd.uuid" when
> creating the pretty print string. It fails in process_op() and then
> later in pretty_print() prefaces the string w '[[FAILED TO PARSE]"
> follwed by the raw values.
> 
> If I omit that '&', it works. But - I get unacceptable compiler
> warnings from the kernel build - trying to assign to %p.
> 
> So, it's really not 'trace-cmd' per se that is failing, that is
> just where the failure is visible.

Right.

> 
> The 'other' way that we view these CXL events are through monitor
> and ndctl, where we pull the fields directly from the event, and
> don't care about that TP_printk string. uuid_t works fine in that
> case.
> 
> CXL events were not the first to use uuid_t. I see events/afs.h
> using it also. I don't see a difference in their syntax, that would
> makes it work there, while CXL fails. Maybe you do.

I'm guessing they don't work ;-)

> 
> I don't have the environment up at the moment, so I'm just spewing
> from notes and memory. If you need actual duplication, ask me again.
> 
> Thanks for helping w this Steve!
> 

No problem.

I'll can add this to a test event and then update libtraceevent to handle
it. I'm currently working on a new release of the libraries anyway.

-- Steve