[P4-dev] Intrinsic metadata and some other questions

Sandor Laki lakis at elte.hu
Fri Jun 12 08:24:21 EDT 2015

Dear Antonin, All,

If I understand correctly, non-standard intrinsic metadata is always 
target specific. Is there any description on how this kind of metadata 
can be used with the current p4 compiler?
For example in l2_switch target there is an intrinsic_matadata_t with 
four fields. For example, if field lf_field_list is removed from the 
definition, the compiler crashes. However, in the p4 program this field 
is not modified or read at all. So, the question is if it is a bug or a 
normal behavior (meaning that the intrinsic metadata definition is 
determined by the target and cannot be changed by the developer). I 
think this problem is mostly related to l2 programs using core 
functionalities of the underlying hardware.

Another question is that do we understand correctly that according to 
the specification parsing phase can be done in a lazy way, resulting 
that some headers are parsed on-demand based on the tables (matching 
rules) to be applied. In the current implementation of most of the 
switches uses lazy parsing.

My last question is related to the interface of the switch. Do you plan 
to provide a standardized way - e.g. something like that is used by 
openflow between switches and controllers?

Thank you in advance!


Sándor Laki
Department of Information Systems
Eötvös Loránd University
Pázmány Péter stny. 1/C
H-1117, Budapest, Hungary
Room 2.506
Web: http://lakis.web.elte.hu
Phone: +36 1 372 2869 /
Cell: +36 70 374 2646

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