Re: [PATCH v2 1/2] tracing/hist: rebuild full_name on each hist_field_name() call

[Steven Rostedt <rostedt@goodmis.org>]

On Wed, 08 Apr 2026 10:58:06 -0500
Tom Zanussi <zanussi@kernel.org> wrote:

Hi Tom,

> ->system is set when using fully-qualified variable names. For  
> instance:
> 
> echo 'hist:keys=pid:ts0=common_timestamp.usecs' >> sys/kernel/debug/tracing/events/sched/sched_waking/trigger
> echo 'hist:keys=pid:ts0=common_timestamp.usecs' >> /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger
> echo 'hist:keys=next_pid:lat0=common_timestamp.usecs-sched.sched_waking.$ts0:lat1=common_timestamp.usecs-sched.sched_wakeup.$ts0' >> /sys/kernel/debug/tracing/events/sched/sched_switch/trigger
> echo 'hist:keys=next_pid:vals=$lat0,$lat1' >> /sys/kernel/debug/tracing/events/sched/sched_switch/trigger
> 
> Here, the sched_switch trigger would error out if the unqualified $ts0
> variables were used instead of the fully-qualified ones because there's
> no way to distinguish which $ts0 was meant.
> 

Yep I see that now. I never had a need to use it before, but I probably
should implement this in libtracefs to be safe.

We should definitely add a selftest that tests this. There's one case that
does use it but it doesn't use multiple ones. We should add a test that
does so.

trigger-multi-actions-accept.tc has the system, but it's not needed here.

We should also have a test to test the output of theses lines.

-- Steve