[lttng-dev] Looking for documentation on the old LTTng traceformats, 2.3-2.6

[David Lindström]

Hi,

Thank you for your reply, however that document appears to apply to the 0.x
or 1.0 version of the LTTng 0.x trace formats.

The 2.3 document[1] seems to match at least the metadata format of a 2.6
trace I have, but it's a bit scary not knowing what changes were made,
especially if these were rather small or rare-case fixes.

For example, the format/version changelog mentions the following for the 2.4
version of the format:

"LTTng 0.170 and LTTV 0.12.21 fixes gcc structure trace format
compatibility. "

What does that mean and what cases does it break? Does it even break
anything or was there just slight changes to the code to better cope with
the latest version of GCC?

For version 2.5, the following is noted:

"LTTng 0.173, ltt-control 0.76, lttv 0.12.22, trace format 2.5 add support
for variable-sized subbuffer transfers. Useful for network trace streaming
with a periodic timer to flush the buffers periodically: only the actual
payload (aligned to the next page) will be sent."

I don't really understand why this was a breaking change to the binary
format since it already had fields for subbuffer sizes and usages..?

2.6 notes the following:

"LTTng 0.191, LTTV 0.12.30 coming with trace format 2.6 revert to the
pre-2.4 behavior for alignment of 64-bit fields on 32-bit architectures. It
aligns them on 32-bit (maximum alignment is the architecture size). This
follows gcc behavior."

This makes me guess the changes in 2.4 was to align 64-bit fields on 64-bits
even on 32-bit platforms. So how does the alignment field in the headers
come into play?

[1] LTTng Trace Binary Format v2.3 Guidelines, Philippe Proulx, 2009 -
http://git.dorsal.polymtl.ca/?p=lttng-dev-doc.git;a=blob_plain;f=trace-format/format.pdf

Mvh
David Lindström

(Sorry for the double reply, I thought the list would be the reply-to 
address for some reason)

-----Original Message----- 
From: Mathieu Desnoyers
Sent: Monday, August 05, 2013 4:38 PM
To: DavidLindström
Cc: lttng-dev at lists.lttng.org
Subject: Re: [lttng-dev] Looking for documentation on the old LTTng 
traceformats, 2.3-2.6

* David Lindström (david.lindstrom at percepio.se) wrote:
> Hi,
>
> I’m looking for documentation on the old/legacy LTTng trace formats.
> Before LTTng 2.x and CTF that is. I found a PDF titled "LTTng Trace
> Binary Format v2.3 Guidelines" which details the 2.3 format nicely.
> However, I need to support the later versions as well which I'm unable to
> find anything at all about. What changed between 2.3 and 2.6?
>
> Does such documentation even exists? If not, what would be my best
> options to figure it out?

I remember someone contributed this kind of documentation in the past.
Here it is:

http://benno.id.au/docs/lttng_data_format.pml

I'm unsure which version of the format it applies to though. It's best
to confirm if it matches the source files before assuming it fits lttng
0.x trace format 2.6.

Good luck!

Mathieu

>
> Mvh
> David Lindström
>
>
> _______________________________________________
> lttng-dev mailing list
> lttng-dev at lists.lttng.org
> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com