Re: Re: [PATCH V4 1/5] trace-cmd/listen: Apply the trace-msg protocol for communication between a server and clients

[Yoshihiro YUNOMAE]

Hi Steven,

Thank you for your review.

(2014/07/23 0:04), Steven Rostedt wrote:
> Sorry for taking so long to reply, I've been hacking on the kernel a
> bit and that takes precedence over user tools :-/
>
>
> On Fri, 11 Jul 2014 00:58:26 +0000
> Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@xxxxxxxxxxx> wrote:
>
> > Apply trace-msg protocol for communication between a server and clients.
> >
> > Currently, trace-listen(server) and trace-record -N(client) operate as follows:
> >
> >       <server>                 <client>
> >        listen to socket fd
> >                                connect to socket fd
> >        accept the client
> >        send "tracecmd"
> >                 +------------> receive "tracecmd"
> >                                check "tracecmd"
> >                                send cpus
> >        receive cpus <------------+
> >        print "cpus=XXX"
> >                                send pagesize
> >                                  |
> >        receive pagesize <--------+
> >        print "pagesize=XXX"
> >                                send option
> >                                  |
> >        receive option <----------+
> >        understand option
> >        send port_array
> >                 +------------> receive port_array
> >                                understand port_array
> >                                send meta data
> >        receive meta data <-------+
> >        record meta data
> >                          (snip)
> >        read block
> >       --- start sending trace data on child processes ---
> >
> >       --- When client finishes sending trace data ---
> >                                close(socket fd)
> >        read size = 0
> >        close(socket fd)
> >
> > All messages are unstructured character strings, so server(client) using the
> > protocol must parse the unstructured messages. Since it is hard to
> > add complex contents in the protocol, structured binary message trace-msg
> > is introduced as the communication protocol.
> >
> > By applying this patch, server and client operate as follows:
> >
> >       <server>                 <client>
> >        listen to socket fd
> >                                connect to socket fd
> >        accept the client
> >        send "tracecmd"
> >                 +------------> receive "tracecmd"
> >                                check "tracecmd"
> >                                send "V2\0<MAGIC_NUMBER>\00" as the v2 protocol
>
> Lets change this to "-1V2\0<MAGIC_NUMBER>\00"
>
> The -1 will cause an old server to exit as it will not accept a -1 for
> CPU count. Then you can check if the return of the next read is -1, as
> the client would have disconnected.

Sure.

> The reason I ask this, is because once you send a valid CPU count (and
> unfortunately, 0 happens to be valid :-p, the server side creates a
> file. When you close it, that file stays around as zero length.
>
> By sending -1, the old server will error out and never create a file.

Yes, I also thought this should be fixed.
I'll submit fixed patch.

Thank you,
Yoshihiro YUNOMAE

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


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