Re: [PATCH v8 11/11] tracing/user_events: Limit global user_event count

[Steven Rostedt]

On Fri, 24 Mar 2023 09:43:53 -0700
Beau Belgrave <beaub@xxxxxxxxxxxxxxxxxxx> wrote:

> > It was actually merged in 5.8. So sysctl should be sufficient with that.
> > But maybe it's weird to start adding sysctls, when the rest of tracing
> > tunables is AFAIK under /sys/kernel/tracing/ ?
> >   
> 
> During the TraceFS meetings Steven runs I was asked to add a boot
> parameter and sysctl for user_events to limit the max.
> 
> To me, it seems when user_events moves toward namespace awareness
> sysctl might be easier to use from within a namespace to turn knobs.
> 
> Happy to change to whatever, but I want to see Steven and Masami agree
> on the approach before doing so.
> 
> Steven, do you agree with Masami to move to just sysctl?

We do have some tracing related sysctls already:

# cd /proc/sys/kernel
# ls *trace*
ftrace_dump_on_oops  oops_all_cpu_backtrace  traceoff_on_warning
ftrace_enabled       stack_tracer_enabled    tracepoint_printk

Although I would love to deprecated ftrace_enable as that now has a
control in tracefs, but it's not unprecedented to have tracing tunables as
sysctl.

And if we get cmdline boot parameters for free from sysctls then all the
better.

-- Steve