linux-kernel - Re: 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: <521DDF49.1090301@hitachi.com>
Date:	Wed, 28 Aug 2013 20:30:17 +0900
From:	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
To:	Steven Rostedt <rostedt@...dmis.org>
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: Re: [RFC PATCH 08/11] trace-cmd: Apply the trace-msg protocol
 for communication between a server and clients

(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"?

Thanks,
Yoshihiro YUNOMAE

-- 
Yoshihiro YUNOMAE
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: yoshihiro.yunomae.ez@...achi.com

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