linux-kernel - Re: [RFC PATCH 08/11] trace-cmd: Apply the trace-msg protocol for communication between a server and clients

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Message-ID: <20130828104249.3533bece@gandalf.local.home>
Date:	Wed, 28 Aug 2013 10:42:49 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
Cc:	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org, yrl.pp-manager.tt@...achi.com
Subject: Re: [RFC PATCH 08/11] trace-cmd: Apply the trace-msg protocol for
 communication between a server and clients

On Wed, 28 Aug 2013 20:30:17 +0900
Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com> wrote:

> (2013/08/27 22:05), Steven Rostedt wrote:
> > On Tue, 27 Aug 2013 19:23:24 +0900
> > Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com> wrote:
> >
> >> OK, let me check that. Even if the old server will receive "V2", the
> >> server will send port numbers instead of "V2" due to the old protocol.
> >> In that time, the new client will disconnect from the old server and
> >> the restarts with the old protocol. Is it OK?
> >
> > Yep, that's exactly what I meant ;-)
> 
> I tried to implement the feature, but I found that sending just "V2"
> from the new client is inappropriate. This is because the old server
> doesn't respond to the client before receiving cpu numbers, page size,
> and options. So, when the new client sends the first message, it should
> send "V2\0<MAGIC_NUMBER>\00\0", I think. If so, the old server will
> understand the message as cpus=0, pagesize=<MAGIC_NUMBER>, options=0,
> and then it will send port numbers(actually \0). Note if <MAGIC_NUMBER>
> is zero, the old server will die.
> 
> Can I implement the first message of the new client as
> "V2\0<MAGIC_NUMBER>\00\0"?
> 

If it works for both old and new server with old and new client (and
all combinations) I'm fine with it.

Thanks,

-- Steve
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