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Date: Wed, 6 Aug 2014 11:41:22 +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>
Cc: =?utf-8?B?cWVtdS1kZXZlbA==?= <qemu-devel@nongnu.org>, =?utf-8?B?QWxleCBCZW5uw6ll?= <alex.bennee@linaro.org>, =?utf-8?B?V2lsbGlhbSBEYXVjaHk=?= <wdauchy@gmail.com>, =?utf-8?B?QW5kcmVhc19Gw6RyYmVy?= <afaerber@suse.de>

>>>>> 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.
>>
>
>This sounds out-of-scope for QEMU to me and makes a standard flow
>non-standard. If prints are going to stderr where should be going
>elsewhere they probably should be fixed. Do you have specific examples
>of information going to stderr that you would rather go to a log (be
>it an error log or something else?).
>
I use proxmox to manage vm, it dose not redirect qemu's stderr, and start vm with -daemonize option,
so the error log disappeared.
I want to redirect the error log of qemu to a specified logfile, if fault happened, I can use the error log to analyze the fault.

And, why qemu output the error log to stderr instead of a error logfile which can be configure?
Thanks,
Zhang Haoyu

>Regards,
>Peter
>
>> 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