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




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