[PATCH v10 08/10] dyndbg: add print-to-tracefs, selftest with it - RFC

[jim.cromie at gmail.com]

On Fri, Nov 12, 2021 at 4:49 AM Vincent Whitchurch
<vincent.whitchurch at axis.com> wrote:
>
> On Thu, Nov 11, 2021 at 03:02:04PM -0700, Jim Cromie wrote:
> > Dynamic-Debug can do 2nd exceedingly well:
> >
> > A- all work is behind jump-label's NOOP, zero off cost.
> > B- exact site selectivity, precisely the useful traffic.
> >    can tailor enabled set interactively, at shell.
> >
> > Since the tracefs interface is effective for drm (the threads suggest
> > so), adding that interface to dynamic-debug has real potential for
> > everyone including drm.
> >
> > Add a new +T flag to enable tracing, independent of +p, and add and

>
> I posted a patchset a while ago to do something very similar, but that
> got stalled for some reason and I unfortunately didn't follow it up:
>
>  https://lore.kernel.org/lkml/20200825153338.17061-1-vincent.whitchurch@axis.com/
>
> A key difference between that patchset and this patch (besides that
> small fact that I used +x instead of +T) was that my patchset allowed
> the dyndbg trace to be emitted to the main buffer and did not force them
> to be in an instance-specific buffer.
>
> That feature is quite important at least for my use case since I often
> use dyndbg combined with function tracing, and the latter doesn't work
> on non-main instances according to Documentation/trace/ftrace.rst.
>
> For example, here's a random example of a bootargs from one of my recent
> debugging sessions:
>
>  trace_event=printk:* ftrace_filter=_mmc*,mmc*,sd*,dw_mci*,mci*
>  ftrace=function trace_buf_size=20M dyndbg="file drivers/mmc/* +x"
>

Hi Vincent,

are you planning to dust this patchset off and resubmit it ?

Ive been playing with it and learning ftrace (decade+ late),
I found your boot-line example very helpful as 1st steps
(still havent even tried the filtering)


with these adjustments (voiced partly to test my understanding)
I would support it, and rework my patchset to use it.

- change flag to -e, good mnemonics for event/trace-event
   T is good too, but uppercase, no need to go there.

- include/trace/events/dyndbg.h - separate file, not mixed with print.h
  dyndbg class, so trace_event=dyndbg:*

- 1 event type per pr_debug, dev_dbg, netdev_dbg ? ibdev_dbg ?
  with the extra args: descriptor that Steven wanted,
  probably also struct <|net|ib>dev

If youre too busy for a while, I'd eventually take a (slow) run at it.