Re: [PATCH] Snoop SET FEATURES - WRITE CACHE ENABLE/DISABLE command

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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.

	Jeff



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