Some commands might need to run longer than the default timeout of
five seconds. If that occurred, run_serial() returned with a status
code of zero (sic!) and no other indication of what went wrong.
Now the timeout is configurable (with five still the default) and
an explicit warning ("<<< run_serial(): command timed out after 5 seconds without output >>>")
gets appended at the end of the data returned to the caller.
While at it, the logic for checking for the timeout was updated a bit
because both implementations could overshoot the timeout when entering
select() right before the final deadline.
Signed-off-by: Patrick Ohly <patrick.ohly@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
