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Date: Wed, 6 Aug 2014 09:23:26 +0800
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Subject: Re: [Qemu-devel] =?utf-8?q?=5Bquestions=5D_about_qemu_log?=
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To: =?utf-8?B?UGV0ZXIgQ3Jvc3Rod2FpdGU=?= <peter.crosthwaite@xilinx.com>, =?utf-8?B?V2lsbGlhbSBEYXVjaHk=?= <wdauchy@gmail.com>
Cc: =?utf-8?B?QWxleCBCZW5uw6ll?= <alex.bennee@linaro.org>, =?utf-8?B?QW5kcmVhc19Gw6RyYmVy?= <afaerber@suse.de>, =?utf-8?B?cWVtdS1kZXZlbA==?= <qemu-devel@nongnu.org>

>>> The output is on qemu's stderr.  You are in control of what that stderr is.
>>
>> I don't get why we can configure
>> -D /path/to/unique/file/name.log
>>
>> but we also have to redirect stderr (I didn't checked if the daemonize
>> option was closing it). What's the purpose of this logfile option?
>>
>
>Well -D will log to file only loggable (i.e. qemu_log()) information
>(which has all sorts of options and switches). Stderr, is a little
>more static and should in theory be limited to genuine errors. But if
>you want a combined log of both you can simply omit -D to default
>qemu_log output to stderr. This gives you a combined log that you can
>redirect anywhere. To be honest, this is what I do as a matter of
>course (2> foo rather than -D foo).
>
Maybe we can introduce a new qemu option to specify a error logfile where stderr be redirected, like below,
DEF("elogfile", HAS_ARG, QEMU_OPTION_elogfile, \
    "-elogfile logfile      redirect stderr log to logfile(default /var/log/qemu/<vm name>##.log)\n",
    QEMU_ARCH_ALL)
STEXI
@item -elogfile @var{logfile}
@findex -elogfile
redirect stderr in @var{logfile} 
ETEXI
then we can set the error log file through qemu command, /var/log/qemu/<vm name>##.log as default.

Thanks,
Zhang Haoyu

>There's plently of tree wide work to clean up the cases where stderr
>is used where qemu_log should be. If you are finding that log
>information is going to stderr instead of the log, patches would be
>welcome.
>
>Regards,
>Peter