Re: [PATCH v7 00/16] tracing: probeevent: Improve fetcharg features

[Masami Hiramatsu]

On Sat, 5 May 2018 11:38:03 +0900
Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:

> On Fri, 4 May 2018 12:06:42 -0400
> Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> 
> > On Sat, 5 May 2018 00:48:28 +0900
> > Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
> > 
> > > So the syntax will be
> > > 
> > > p[:EVENT] SYM[(CAST)|+OFFS] [FETCHARG]
> > > 
> > > And here is an example;
> > > 
> > > p:myevent vfs_read(void *file, char *buf, size_t count, void *pos) $arg1 $arg2
> > 
> > If we do this, why bother with $arg1 $arg2?
> 
> User may want to trace only some of them. :)
> 

OK, now I think it is a time to introduce new unified interface for dynamic events,
tracefs/dynamic_events and make uprobe_events and kprobe_events as symbolic-links
to the new interface file.

Actually, there is no reason we split those 2 interfaces, since
both have similar, but very clear syntax differences.

o Uprobe event definition
  p[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a uprobe
  r[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a return uprobe (uretprobe)
  -:[GRP/]EVENT                           : Clear uprobe or uretprobe event

o Kprobe event definition
  p[:[GRP/]EVENT] [MOD:]SYM[+offs]|MEMADDR [FETCHARGS]  : Set a probe
  r[MAXACTIVE][:[GRP/]EVENT] [MOD:]SYM[+0] [FETCHARGS]  : Set a return probe
  -:[GRP/]EVENT                                         : Clear a probe

At first, it is clear that those can share the parser. 2nd, it is easy to
distinguish those, because Uprobe event must require the PATH which starts
with '/', on the other hand, Kprobe event must NOT start with '/'.
(both SYM and MOD will start with alphabet or '_', of course MEMADDR
will start with digits)

If we can merge those to unified dynamic_events interface, I think
'f[:[GRP/]EVENT] SYM(CAST)' is also acceptable, since it is no more
only for kprobe/uprobe. We can directly add some other dynamic
events via dynamic_events interface. ;)

Thank you,

-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>