Messages in this thread | | | From | Jarod Wilson <> | Subject | Re: [PATCH update] firewire: fix "kobject_add failed for fw* with -EEXIST" | Date | Mon, 28 Jan 2008 17:24:11 -0500 |
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On Monday 28 January 2008 01:54:14 pm Stefan Richter wrote: > Jarod Wilson wrote: > > We may have another issue there though, as when this happened to me, the > > md layer apparently never noticed (after ~6 hours) that one of the array > > members had disappeared -- not sure if that's firewire's fault or md's > > though... This will presumably avoid this situation entirely, but worth > > noting that there may still be somewhere we need to better communicate > > status to an upper layer. > > I don't know how md ticks, so I have no idea what might have happened > there.
It looks like firewire is doing the right thing, unregistering the fw* device, and the SCSI layer is subsequently removing the appropriate /dev/sd* nodes, but for whatever reason, md hasn't a clue this has happened. I can reproduce this particular part of the problem by bringing the array up, and then simply pulling the firewire cable on one of the drives in the array...
> Somewhat related: What if > - we lose connection to disk "A", represented by scsi_device "a", > - the SCSI core sets "a" offline, > - we gain connection to disk "A" again (i.e. it only shortly > disappeared from the bus from firewire-core's and -sbp2's point > of view), > - and firewire-sbp2 adds it as scsi_device "b", even before SCSI > core got rid of "a"? > No big problem for stand-alone volumes (unless it happens when the > volume is in use), but maybe trouble for md managed volumes.
That does appear to be the case. If I reconnect the drive I disconnected, which was originally /dev/sdb, it comes back up as /dev/sdd now. So apparently, the scsi layer is at least bright enough to see that someone (md) is still trying to use /dev/sdb, but I'm clueless as to why md doesn't have any idea that /dev/sdb actually went away. :\
> To smooth such issues out, my longer term goal was to allow brief > periods of disconnection in (firewire-)sbp2. I.e. the SCSI core > wouldn't notice that "A"/"a" went away, it would only notice that "a" > wasn't accessible for a short time. I think the Fibre Channel drivers > already support this. The ieee1394 driver even has a "limbo" for > devices which went away, in order to remember them until they come back, > but sbp2 doesn't use this feature. (Nobody did the work to enhance sbp2 > to utilize the feature.) > > BTW, if you unplug and replug a FireWire disk under Mac OS X fairly > quickly, OS X will pretend that nothing happened and let the user > continue using the disk if he hadn't "ejected" it before the brief > connection loss.
Certainly sounds like a feature we'd benefit from having in this particular case...
> Anyhow, we have a few more urgent problems to solve in firewire-sbp2's > reconnection handling before we can think about such extras.
Very true... Perhaps I'll just file this one away a bit down the TODO list for now... ;)
-- Jarod Wilson jwilson@redhat.com
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