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

Stefan Richter
2009-12-26T14:33:26Z

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.)