[Discuss-gnuradio] Custom OFDM Carrier Allocator block

Hi,

I have duplicated the OFDM Carrier Allocator block, because I would that the
occupied carriers parameter was not a variable but an input of the
block. I added this:

tagged_stream_block("allocator_alix",
gr::io_signature::make2(2, 2, sizeof(gr_complex),
sizeof(int)),
gr::io_signature::make(1, 1, sizeof(gr_complex) *
fft_len), len_tag_key),
d_fft_len(fft_len),

...


and I added right line in the .xml file.
When I execute the flow graph in GRC this is the error that I see:

gr::log :FATAL: allocator_alix0 - Missing a required length tag on port
1 at item #0
thread[thread-per-block[11]: <block allocator_alix (12)>]: Missing
length tag.

I don't understand what I have to do for solve this.
I have attached part of the flow graph.
Thanks in advance,

Alice