On 09/29/2012 06:31 PM, Rafael J. Wysocki wrote:
On Saturday, September 29, 2012, Alan Stern wrote:
Can arbitrary SCSI devices be ZP, or does this notion apply only to
ATAPI-based drives? That's the key question, and the answer determines
where the ZP support belongs.
I agree. That said for now I'm not aware of any other ZP devices. It also
is unclear whether or not their requirements would be the same for the
ZPODD devices.
Not quite.
The key question is whether or not this operates at the SCSI command set
level. ATAPI is simply SCSI MMC command set tunnelling.
The ATA-specific bits that belong in libata include everything below the
SCSI command set: bus details, delivering the command to the device,
returning the command response, etc.
sr handles the SCSI command set details. SATA optical devices are
aligned with the SCSI MMC command set, which periodically synchronizes
with USB and ATAPI industry efforts.
There are ugly hacks around the edges, where sometimes ATA or USB
subsystems may tweak the request or response in passing, but that is the
general model: it belongs in libata UNLESS the operation is occurring
wholly at the SCSI command set level.
Because USB and ATA chose to use the SCSI command set, it is sadly
inevitable that there might be a few details -- hopefully glossed over
with layer-hopping hooks and flags -- within 'sr' that are bus-specific.
The simple fact of "only ZPODD devices out there are ATA" is not the
decision-maker for where the code should live. It is more a question
where ZPODD belongs in the device/command set model currently employed.
Jeff
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