[Discuss-gnuradio] Tag propagation policy for tagged stream blocks

[Johannes Demel]

Hey everyone,

I have an issue with how additional tags are handled in 'tagged stream 
blocks'.
E.g. think of a 'FEC Tagged Encoder'. It does handle the length tag but 
what happens to other tags? They are left untouched. This results in a 
situation where a rate change basically makes all other tags disappear 
because these tags will be out of range for all other blocks down the line.
Right now, the options are to not use tags, implement custom blocks that 
exhibit the desired behavior, or implement the desired behavior in the 
GR source. Though, that'll force users to permanently move to a 
different GR source. A situation that is really undesirable.

What I'd like to have is a tag propagation policy that takes all tags in 
range and moves them to the correct output range. Maybe all of them to 
the same position as the length tag. Or a policy that honors the length 
tag position and the rate change for the currently processed samples.
Maybe we could switch between the current and the new tag propagation 
policy.
Since this might be a change that has quite some impact I'd like to 
discuss it and decide later how I'll move forward.

Cheers
Johannes