[lustre-devel] Error checking for llapi_hsm_action_progress().

[NeilBrown <neilb@suse.de>]

I have a question about llapi_hsm_action_progress().  The documentation
says that every interval sent "must" be unique, and must not overlap
(which not exactly the same as 'unique').  The code (on server side)
only partially enforces this.  It causes any request for an empty
interval (start>end) to fail, but otherwise accepts any interval.  If it
gets two identical intervals (not just overlapping, but identical), it
ignores the second.  This seems weird.

It would make some sense to just accept any interval - all it does is
sum the lengths, and use this to report status, so no corruption would
result.  It would also make sense to return an error if an interval
overlaps any previous interval, as this violates the spec.  It might
make sense to accept any interval, but only count the overlapped length
once.  But the current behaviour of only ignoring exact duplicates is
weird.  I tried removing that check, but there is a test (hsm_test 108)
which checks for repeating identical intervals.

I want to clean up this code as I'm converting all users of the lustre
interval-tree to use the upstream-linux interval tree code.  What should
I do?

Should I remove test 108 because it is only testing one particular
corner case, or should I improve the code to handle all overlaps
consistently?  Would it be OK to fail an overlap (I'd need to change
test 108), it must they be quietly accepted?

Thanks,
NeilBrown
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