On Wed, 22 Jun 2005, Luben Tuikov wrote: > For the success of the state machine, states must be discrete. > scsi_remove_host() cannot mean "reasonably soon". If it _has_ to mean > that, then _add_ another state. > > If one wants to consolidate the hot-unplugging with notified unplug, > one might as well aim for the supercase "hot-unplug". Its implementation > would surely satisfy notified unplug. Certainly. In the UNPLUG_NOTIFY state, only commands like SYNCHRONIZE CACHE should be allowed. > The lower layers should make sure that if the device is gone, that is > they _know_ about the event, an error is returned. > > So that the treatment of flush-cache is no different than already queued > commands. For the unplug case you are right. For the notify case it's a little tricky because of the interaction with command cancellation (if commands need to be cancelled) and the need to allow the cache flush without allowing other commands. > So in effect, you (usb-storage) know about a condition (say device is gone) > you should act on it right in queuecommand() and not accept the command, > as opposed to hoping for the midlayer to turn around and preempt those commands. > > Luben > P.S. USB is perfect, since you're notified on unplug. Yes. But in fact usb-storage has a small loophole. Before calling scsi_remove_host, we set a flag that causes the queuecommand routine to reject all new commands and any currently-executing command to fail-fast. However there is a small window between the time a command is accepted and the time it starts to execute (because execution takes place in a separate kernel thread). If a command has been accepted and has not started to execute, then usb-storage doesn't cancel it. We've been relying on the midlayer to cancel it for us. There's no reason usb-storage can't cancel the command before calling scsi_remove_host. I tried out a patch to do just that, and it worked fine. (Waiting until after scsi_remove_host to cancel the command doesn't work, for the obvious reason that the midlayer may have already cancelled it.) I'll submit the patch; it should solve this particular problem for usb-storage. I don't know how any other hot-unpluggable LLDDs will handle cancellation during unplug. Alan Stern - : send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
