@shahor02 did you mean something like this? I used the UserField as it was completely available.

I also took the chance to set the cluster pattern in the tracker itself.
This is likely to be overwritten if we use the executable:

We could consider to remove it from the trackerSpec

1. I thought you will add this feature on top of the [ITS-tracking] Use MCTruthContainer to manage MC labels #6431, so that the fakes pattern would profit from all labels in the MCTruthContainer

This is a no-issue to me, I was just being orthogonal to that just in case we decided to merge this first (as this does not affect the I/O of the tracker and results easier to integrate on the multi roframe stuff). I can close this PR and update #6431.

2. I would keep the user field for transient info, in the TrackITS we have currently
   

   AliceO2/DataFormats/Detectors/ITSMFT/ITS/include/DataFormatsITS/TrackITS.h

   Line 99 in fc78990

   uint16_t mPattern = 0; ///< layers pattern

   
   The in-memory size of the TrackITS will not increase from extending it to 32 bytes and using upper 16 for the fakes pattern (with corresponding getters).

True, I'll do that.

Also, I agree that once the patterns are set in the tracker itself, we can suppress this part in the spec (but then the same should be implemented in the @iouribelikov's tracker).

Aren't anyways the two *TrackerSpecs separate?

Aren't anyways the two *TrackerSpecs separate?

Right!

Ok, closing here as I am porting these changes to #6431.