Tejun Heo wrote:
Jeff Garzik wrote:
Tejun Heo wrote:
Jeff Garzik wrote:
4) Using [__]scsi_add_device() is a regression from using
scsi_scan_target()
I think it's taken from the hotplug patch
store-attached-SCSI-device[1]. Using [__]scsi_add_device() seems to
be the only way to reliably obtain the attached sdev.
We want to continue to use scsi_scan_target(), because that's the
preferred model. In SCSI-land, the target is what receives RPC calls
(ATA commands, for us), which are then dispatched internally to one of
$N logical units (LU) according to the logical unit number (LUN).
In libata, of course, there is only one logical unit attached to the
target, LUN 0.
Regardless, using [__]scsi_add_device() is a regression, because
libata handles the transport layer completely -- and importantly --
handles all addressing. scsi_add_device() is specifically for
H/C/I/L, i.e. SPI (parallel SCSI) addressing.
Eventually SCSI will reach a point where HCIL is not the only
addressing method. SAS disks, for example, are addressed via a LUN's
WWN. SCSI fibre channel addresses LUNs via WWN as well. Once SCSI
core does not exclusively use HCIL addressing, libata will reap the
benefits of using the proper scsi_target model.
I fully agree with everything you said, but we're faced with a real
problem here. libata needs to know the current attached sdev for
hotplug and rescan; however, there's no way to determine the current
sdev after it's already added.
[looks at the core code again] That's not the problem. The real
problem is that scsi_target hotplug infrastructure is non-existent.
scsi_transport_fc gives a hint as to how nasty it would be to add such
code, too.
So, life sucks. Oh well. Your solution is therefore the best, under
present circumstances. ACK use of [__]scsi_add_device().
Jeff
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