[lttng-dev] "No space left on device" results in corrupt trace data set

[Woegerer, Paul]

On 11/16/2012 04:43 PM, Yannick Brosseau wrote:
> It could be interesting to at least reserve the size for the first
> packet, so we have at least a little bit of information on the trace.

I tried that with fallocate but unfortunately tmpfs does not seem to
support fallocating files :(

--
Paul

> 
> On 2012-11-16 10:29, David Goulet wrote:
>> Hi Paul,
>>
>> The problem here would be that metadata can grow arbitrarily over time
>> when let say new events are enabled during tracing or a new lib is
>> dynamically loaded in the application you are tracing. Same goes for the
>> kernel for loaded module or CPU hotplug...
>>
>> To achieve a static size of metadata during the whole life of a tracing
>> session, I guess we need somekind of flag or option set to tell the
>> tracers to just deny new events once started... which from there, we
>> need Mathieu's opinion :)
>>
>> Cheers!
>> David
>>
>> Woegerer, Paul:
>>> Hi,
>>>
>>> embedded users sometimes have to trace to tmpfs (e.g. streaming in not
>>> an option due to missing network connectivity).
>>>
>>> Ramdisks of 16M to 128M size are created and as long as the ram disk
>>> does not get full, tracing works fine. Unfortunately if the disk gets
>>> full things fall apart:
>>>
>>> PERROR: Error in file write: No space left on device [in
>>> lttng_consumer_on_read_subbuffer_mmap() at consumer.c:1367]
>>>
>>> The consumer daemon will not be able to write the metadata channel and
>>> therefore the trace data set will be unusable (cannot be read with
>>> babeltrace).
>>>
>>> -rwxrwxrwx 1 testuser users        0 Nov 16 11:22 metadata
>>> -rwxrwxrwx 1 testuser users 15728640 Nov 16 11:22 myevents_0
>>> -rwxrwxrwx 1 testuser users     4096 Nov 16 11:22 myevents_1
>>>
>>> Is it possible to somehow reserve the file size (fallocate) for metadata
>>> so that in case the disk gets full at least the metadata gets written
>>> and the resulting trace set is readable with babeltrace ?
>>>
>>> I wonder if that is possible at all. The consumer daemon doesn't know
>>> upfront how much would need to be reserved for metadata, right ?
>>>
>>> Any ideas ?
>>>
>>> Thanks,
>>> Paul
>>>
>>>
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> 
> 
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-- 
Paul Woegerer | SW Development Engineer
http://go.mentor.com/sourceryanalyzer

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