On May 8, 2008, at 7:50 AM, Jeff Squyres wrote:
> - I think "none" is a slightly better word than "null" for this value;
> "none" implies that you don't open anything, whereas "null" could be a
> specific component (as it is/was in some frameworks).
Calling it 'none' sounds fine to me.
> - Whatever word we decide on will need to become a reserved component
> name (i.e., no components will be able to use that as their name). We
> should adjust autogen.sh and friends to ensure that no component has
> this name (not difficult -- just make autogen.sh abort if it finds a
> component of this name).
> - Is this value supposed to be accessible/usable by users, or is it
> meant to only be used internally?
I would say it should be used internally. But I don't know what use
case Ralph was thinking of with this.
There is something to be said for being able to add such an option to
the .openmpi/mca-params.conf file while testing or to an AMCA file
for a particular configuration. So maybe we should expose it. It may
able be useful for debugging problems encountered in the wild.
> --> If intended to be used by users, I marginally prefer a single,
> lower case, simple word (e.g., "none") vs. a caps word -- it's easier
> to type and is consistent with our other values. I recognize that we
> don't want users to use the value by accident, and making it all caps
> makes it stand out, but I think the consistency issues are more
Keeping it case-consistent with other components is probably a good
> --> If not intended to be used by users (i.e., it's an internal
> mechanism only), is there a reason why we're not using a zero-length
> string (e.g., mpirun --mca foo "")?
I think a zero length string might get confusing with the empty
string. The empty string is taken to mean auto-select from all
available components, which currently cannot be specified on the
command line as an -mca option. The 0 length string is close and
nearly indistinguishable in an (A)MCA file from a NULL string.
> On May 6, 2008, at 2:09 PM, Josh Hursey wrote:
>> What: Add a MCA-NULL option to open no components in mca_base_open()
>> Why: Sometimes we do not want to open or select any components of
>> a framework.
>> Where: patch attached for current trunk.
>> When: Needs further discussion.
>> Timeout: Unknown. [May 13, 2008 (After teleconf)?]
>> Short Version:
>> This RFC is intended to continue discussion on the thread started
>> Discussion should occur on list, but maybe try to come to some
>> settlement on this RFC in the next week or two.
>> Longer Version:
>> Currently there is no way to express to the MCA system that
>> absolutely no components of a framework are needed and therefore
>> nothing should be opened. The addition of a sentinel value is needed
>> to explicitly express this intention. It was suggested that if a
>> 'MCA-NULL' value is passed as an argument for a framework then this
>> should be taken to indicate such an intention.
>> devel mailing list
> Jeff Squyres
> Cisco Systems
> devel mailing list