[ltt-dev] LTTng specialized probes

[md@google.com (Michael Davidson)]

On Tue, Oct 7, 2008 at 5:07 PM, Mathieu Desnoyers <
compudj at krystal.dyndns.org> wrote:

>
> >
> > This conversion could be done in the kernel, by a user space program
> > running on the same machine, or by a program running elsewhere.
>
> You seem to assume that the same ABI the kernel runs in will be
> available elsewhere, which might not be true in the embedded field. The
> same applies to 64-bits x86 kernel with 32-bits userland. Therefore,
> getting data out of the kernel should be done by a standardized ABI;
> ideally following the kernel ABI for speed, but more importantly :
> self-described. This is what LTTng does.
>

I am confused by your response - I think that we are in agreement but may
be using terminology slightly differently.

When I said that the conversion could be done by "a program running
elsewhere"
I was assuming that the metadata  which came along with the raw trace data
would be sufficient to make that possible.

In other words:

- the metadata itself must be in a canonical format (ascii perhaps?) or be
  sufficiently self  describing that it can be interpreted correctly.

- the metadata must completely describe the format of the binary data
  including such things as byte order, size and alignment of data types
  and the mapping of all binary values into a canonical external format
  (ie maps for event numbers to event names, system call numbers to
  system call names etc)

Given that information you can write a portable program which can run
anywhere which can do the conversion.

I am not sure what the mechanism for extracting the trace data from
the kernel and getting it into user space has to do with this.

md
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