Re: [PATCH] dm-mpath: always return reservation conflict

[Christoph Hellwig <hch@lst.de>]

An array can't issue a reservation, the initiator needs to register
it.  Right now the only way to do it is through SG_IO passthrough,
which is a best luck effort it I/O isn't also using SG_IO and can't
be properly supported because of that.

However I will submit an in-kernel reservation API soon which will
allow us to have that sort of control.  My current prototyp only allows
for all-path reservations as I couldn't come up with a use case for
per-path reservations, but if such a need should arise we can add it
and take that into account in the multipathing code.