linux-kernel - Re: [RFC PATCH 0/5] tracing: Unifying dynamic event interface

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Message-Id: <20181002164526.09f93bffa5d543f3a00e1080@kernel.org>
Date:   Tue, 2 Oct 2018 16:45:26 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Tom Zanussi <tom.zanussi@...ux.intel.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>,
        Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH 0/5] tracing: Unifying dynamic event interface

Hi Tom,

On Mon, 01 Oct 2018 08:49:24 -0500
Tom Zanussi <tom.zanussi@...ux.intel.com> wrote:

> Hi Masami,
> 
> On Fri, 2018-09-28 at 00:58 +0900, Masami Hiramatsu wrote:
> > Hi,
> > 
> > This is an RFC series of unifying dynamic event interface on ftrace.
> > Currently ftrace has 3 dynamic event interfaces, kprobes, uprobes
> > and synthetic. This series unifies kprobes and uprobes event
> > interface on "dynamic_events". This enables us to add new dynamic
> > events easily on same interface, e.g. function events.
> 
> This seems like a nice idea to me and I don't see any problems with the
> patches themselves, so consider it
> 
> Acked-by: Tom Zanussi <tom.zanussi@...ux.intel.com>

Thanks!

> 
> > The older interfaces are left on the tracefs for backward
> > compatibility at this moment.
> > 
> > dynamic_events syntax has no different from kprobe_events and
> > uprobe_events. You can use same syntax for dynamic_events interface.
> > 
> > I think we can integrate synthetic events to this dynamic_events
> > interface but it will requires new syntax. e.g.
> > 
> > echo "s:<event-name> <args>" >> dynamic_events
> > 
> 
> So that's just the existing syntax, prefaced by s: , right?

Yes, just for identifying.

> > If it is OK, I'll add it in next version.
> > 
> 
> Makes sense to me.

OK, I'll try :)

> 
> > BTW, since this dynamic_events interface derived from *probe_events,
> > it inherits "all clear when truncate file open" behavior. But if you
> > think this is too aggressive, I can drop it. (even in that case,
> > kprobe_events/uprobe_events behavior is not changed)
> > 
> > I also introduced a widely used way to erase entries in other
> > interfaces of ftrace, that is '!'. So you can now use '!event-name'
> > or '!group/event' to erase an entry in dynamic_events.
> > (Wait... it has to be '!p:event' as others do??)
> > 
> 
> I'd think the full form should always be accepted, but would only be
> necessary in cases requiring disambiguation.

OK, I'll add full form support.

Thank you,


-- 
Masami Hiramatsu <mhiramat@...nel.org>