about mirror cancel

[Vladimir Sementsov-Ogievskiy]

Hi all!

Recently I've implemented fast-cancelling of mirror job: do 
bdrv_cancel_in_flight() in mirror_cancel().

Now I'm in doubt: is it a correct thing? I heard, that mirror-cancel is a kind 
of valid mirror completion..

Looking at documentation:

# Note that if you issue 'block-job-cancel' after 'drive-mirror' has indicated
# (via the event BLOCK_JOB_READY) that the source and destination are
# synchronized, then the event triggered by this command changes to
# BLOCK_JOB_COMPLETED, to indicate that the mirroring has ended and the
# destination now has a point-in-time copy tied to the time of the cancellation.

So, in other words, do we guarantee something to the user, if it calls 
mirror-cancel in ready state? Does this abuse exist in libvirt?

====

Note, that if cancelling all in-flight requests on target is wrong on mirror 
cancel, we still don't have real bug, as the only implementation of 
.bdrv_cancel_in_flight is stopping reconnect waiting in nbd driver. So, we'll 
cancel requests only if connection is already lost anyway.

But that probably means, that correct name of the handler would be 
.bdrv_cancel_in_fligth_requests_that_will_most_probably_fail_anyway()..

And it also means, that abuse of mirror-cancel as valid completion is a bad 
idea, as we can't distinguish the cases when user calls job-cancel to have a 
kind of point-in-time copy, or just to cancel job (and being not interested in 
the final state of target).

So, probably we need an option boolean argument for blockjob-cancel, like 
"hard", that will cancel in-flight writes on target node..

--
Best regards,
Vladimir