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

[Christophe Varoqui]

Le Wed, 22 Oct 2008 14:21:57 -0700,
Chandra Seetharaman <sekharan at us.ibm.com> a écrit :

> 
> 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
> 
> No, the handler doesn't generate the requests.
> 
> Device handler's check_sense() function is called from the
> scsi_error.c:scsi_check_sense() function whenever a sense code is
> returned from the device (on normal I/Os).
> 
> When in the sense function, the device handler can do any action (like
> closing the other path(s)) and returning an appropriate error code
> (such that dm doesn't retry the I/O on other paths).
> 
Thanks for the clarification. I shouldn't have stopped after
reading the hp_sw handler, which does not implement a .check_sense

So now, device handlers indeed look promising. I still see difficulties
though :
1/ reservation conflict is a scmd status, and as such short-cuts the
scsi_check_sense function altogether. Sould we hook device handlers to
status parser too ?
2/ should we create an trivial device handler and load multi-handlers
multipath maps or should we make this device handler implicitly always
active ?

Regards,
cvaroqui