[ltt-dev] Traces data alignment

[Jérôme Stadelmann]

On vendredi 20 mars 2009 15:53:55 Mathieu Desnoyers wrote:
> * Jérôme Stadelmann (jerome.stadelmann at heig-vd.ch) wrote:
> > On jeudi 19 mars 2009 18:00:01 Mathieu Desnoyers wrote:
> > > * Jérôme Stadelmann (jerome.stadelmann at heig-vd.ch) wrote:
> > > > Hi everybody,
> > > > 
> > > > I'm working on a LTTng traces parser and I'm a little bit blocked on the alignment. Can someone please explain how and where it is coded ?
> > > 
> > > The lttv lib "ltttraceread" should do that for you.
> >  
> > > > What are the roles of the alignment defined in the traces header and the one defined in the metadata file in the core_marker_id ?
> > > > 
> > > 
> > > They tell that a specific tracefile content is aligned or not, and if
> > > the content of a given event is aligned or not. You should really have
> > > at least a look at the ltt lib traceread reference implementation.
> > 
> > Thank you. This library helped me a lot. I see that there is an up to 2 byte alignment in the core marker id event definition. Is there the only special case ?
> > I've searched the uses of the ltt_align function. Are there other functions to look for ?
> > 
> 
> Looking at ltt_align use is a good starting point.
> 
> Can you point out to the specific package/version/file/line you refer to
> for the core marker id "special case" you talk about here ?
> 

I'm using the version lttv-0.12.4-18122008 with the Lttng 0.82

in file tracefile.c
function ltt_update_event_size
line 1506 :   size += ltt_align(size, sizeof(guint16), tf->alignment);

I don't understand why an alignment of 2 bytes here.

Jerome

> Mathieu
> 
> > Jerome
> >  
> > > Mathieu
> > > 
> > > > Regards,
> > > > Jerome
> > > > 
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> > > 
> > 
>