Re: [PATCH] make the SCSI mid-layer obey the device online flag

[Luben Tuikov <tluben@rogers.com>]

Christoph Hellwig wrote:
> On Wed, Jun 04, 2003 at 03:14:56PM -0400, James Bottomley wrote:
> 
>>Yes, that's why I think forbidding *all* I/O after offlining is too much
>>effort.  Offlining should be a precursor to device destruction, but
>>actual destruction probably relys on detaching the queue from the block
>>device interface and sitting on it until all use counts drop to zero.
> 
> 
> We need a way to disable _all_ I/O to a device due to the way the driver
> model works.  The driver model ->remove always is a surprise removal,
> so the underlying PCI (or whatever) device for a scsi host can go away
> anytime.  Because of that we need to make damn sure no call to
> ->queuecommand will happen after scsi_remove_host is called.  Whether
> this is implemented with the same mechanisms as the current sdev->online
> is another question.

James was talking about ``device server not ready'' aliased to
online -- i.e. if online is 0 then only INQUIRY or TUR should
be sent from SCSI Core (unless SCSI Core decides to _know_ about
the different ULP).  The semantics on this are somewhat touched
in the INQUIRY description in SPC-3.

(This means that the device is on the SAN, but not ready to
process commands.)

You're talking about hardware removal -- more specifically
logical removal of a host -- in which case of course there's no
_host_, so how can online be checked.... (online being
member of sdev, sdev being parented by shost...)

IOW, you probably need either a flag in shost, to mean that
it's logically removed (whether hdwr or not) until it is
actually gone, or an external flag per host... it's your call.

-- 
Luben