[openib-general] ib_mad.c comments

[Sean Hefty]

>> Personally, for an initial implementation, I'd just go with posting
>> work requests, and generate completions for sends that cannot be
>> posted.  This should be fairly trivial to implement, yet still work.
>
>In that case, it would be sufficient to return an error code to the caller.
>If the caller wants to re-use the completion routine at this point,
>let him.

For sends without a timeout specified, I agree that it makes sense to just
return a failure, but for sends with a timeout, this would prevent the
caller from taking advantage of the access layer tracking the timeout
period.

For example, if the caller tries to resend the MAD immediately, it's likely
to fail again.  It seems like it would be beneficial to indicate the failure
after a given time period, which may give a retry a better chance of
succeeding.

Thinking about this a little more, I'm guessing that the access layer will
already have to allocate a structure to track all sends in order to match
responses with requests, so queuing sends is probably just as easy to
implement now as not.