linux-kernel - Re: [PATCH 1/5] firewire: fix use of multiple AV/C devices, allow multiple FCP listeners

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Message-ID: <4B361EAC.2090605@s5r6.in-berlin.de>
Date:	Sat, 26 Dec 2009 15:33:16 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Pieter Palmers <pieterp@...w.be>
CC:	linux-kernel@...r.kernel.org,
	Clemens Ladisch <cladisch@...tmail.net>,
	linux1394-devel@...ts.sourceforge.net
Subject: Re: [PATCH 1/5] firewire: fix use of multiple AV/C devices, allow
 multiple FCP listeners

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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