[dm-devel] Re: [BUG] dm-mpath and scsi persistent reservation

[James Bottomley]

On Wed, 2008-10-22 at 21:54 +0200, Christophe Varoqui wrote:
> It seems to me the device handler infrastructure proposes to translate
> scsi error codes from requests generated by the device handler itself. I
> don't know how we can detect a reservation conflict from a device
> handler without submitting a dangerous write io.

For SCSI-2 reservations, Test Unit Ready will do this for you.

For SCSI-3, you're right, it's more complex.  You actually have to use
the PR IN commands to read the reservations if you don't want to test
what they'll actually do with an I/O.

> I don't see how we could use a device handler to translate an scsi error
> code from a write io submitted to the multipath device map. Do you ?

Well, there is a problem.  Reservation Conflict should be treated as a
device error and passed straight up ... it shouldn't really have any
effect on dm mp because a path switch is unlikely to fix any issues.  So
dm mp shouldn't be intercepting this type of error at all.

James