they do not have to be the same:
https://www.mcs.anl.gov/research/projects/mpi/mpi-standard/mpi-report-2.0/node47.htm

this is a bit clearer than hard-coding the relation between the request
number and the worker it was sent to

Roland Haas authored May 22, 2017 and Roland Haas committed Jun 09, 2017

this makes sure that only one rank uses O_TRUNC but I can still use
fwrite() to get stdio buffering (for free)

this is mostly so that I don't confuse 'e' for exit and 'E' for error

namely for pax do not ever user ther prefix field

instead look up format description in POSIX

* run testsuite when test script changes
* declare all target as phony

I should also test for huge files, but given that huge files only occur
at 8GB this would be an extensive test

this is not really required in order for the file being a correct pax
file but it makes comparison easier

apparently the last \0 is optional if the file name would otherwise
overflow the field?