Re: Understanding LTT

* VomLehn, David ([email protected]) wrote:
> I am looking at LTT as a good starting point to recording traces for
> post-crash analysis. Unlike what most people are doing, I am developing
> for an embedded system which has no place to store a crash dump. My
> approach is to write the traces to "reserved" memory that won't be
> cleared when the system comes back up. To do this, it looks like the
> approach would be to use flight recorder mode on buffers allocated in
> the reserved areas. Trying to figure out where to splice into LTT to do
> this, however, is somewhat time-consuming as there is less documentation
> in the code than I would prefer. From what I can gather, the LTT code
> looks designed so that it might accommodate a new transport layer that I
> could write to do while I want.
> 
> Is there documentation on LTT buffer allocation outside of the code to
> which I might refer, or can someone give me a few tips on where to
> start? Alternatively, is there a better approach that someone can think
> of?
> 

Yep, it seems like MontaVista's work will find quick use.. I put you in
contact with Maxim Uvarov who is currently implementing a kernel crash
dump trace buffers extractor. I worked with him to get the buffer order
right and to create the ltt_write_commit_count() function that will give
the next versions of LTTng the ability to have a readable "last" buffer,
meaning: the last subbuffer being written when the system crash will be
readable by LTTV.

Basically, what you want is to take a snapshot of your "hot" memory once
the kernel has rebooted and tweak Maxim's tools to extract the buffers
from the kernel memory dump.

Mathieu

> --
> David VomLehn, Staff O/S Software Engineer
> Scientific Atlanta, A Cisco Company
> 10590 N. Tantau Avenue, Cupertino, CA 95014
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-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
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