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List:       linux1394-devel
Subject:    Re: [PATCH 1/5] firewire: fix use of multiple AV/C devices, allow
From:       Stefan Richter <stefanr () s5r6 ! in-berlin ! de>
Date:       2009-12-26 14:33:16
Message-ID: 4B361EAC.2090605 () s5r6 ! in-berlin ! de
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Stefan Richter wrote:
> BTW, what about AV/C RESERVE?  According to the spec, it means that a
> controller gets exclusive FCP access to a target.  At this point, a
> node-wide FCP serializer will have to decide on a policy:

(because the spec does not have a concept of reservation IDs.  It
stupidly takes node IDs for what should be reservation IDs even though
it distinguishes between the concepts of 'controller' and 'node'.)

> The simpler policy would be to remain oblivious of RESERVE.  The more
> difficult to implement policy would be to keep track of reservations
> and only allow a single controller process (or user, or...) to perform
> subsequent transactions for the duration of a reservation.

Err, no, forget that.  A reservation prevents only control commands, but
AFAIU not even all control commands because subunit specifications may
enumerate control commands that are still allowed during a reservation.
So the serializer would have to have knowledge of subunit specs.  That
would quickly get out of hand.

> (I for one would keep it simple.)
-- 
Stefan Richter
-=====-==--= ==-- ==-=-
http://arcgraph.de/sr/

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