On Mon, 2014-08-25 at 10:44 -0400, Alan Stern wrote: > James, can you explain how the INQUIRY command in scsi_probe_lun() > managed to work back in the days when multi-lun SCSI-2 devices were > common? sdev->scsi_level doesn't get set when sdev is allocated, so it > initially contains 0, so the LUN bits won't get filled in when the > first INQUIRY command is sent. Then how could the target know which > logical unit the INQUIRY was meant for?
Best guess, some patches over the course of time altered the way we do this and no-one noticed. I think it was probably the introduction of the unknown SCSI data level that caused the breakage. Historically, the LUN in CMD bits is left over from SCSI-1; it was incorporated into SCSI-2 for backward compatibility (even though SCSI-2 moved the LUN specification to the identify message). In SCSI-3 and beyond, those bits were obsoleted and transports took sole responsibility for LUN handling. I'm fairly certain all the SCSI-1 devices relying on this behaviour have long ago migrated to the great data centre in the sky. Alan's fix looks reasonable because we probe LUN 0 first (for SCSI-1 and 2 which has parallel scanning), which is why it doesn't matter (the bits are set to zero) and once we have LUN 0 we propagate the data to the target and make it the basis for future checks. I'd like to see a comment explaining this in the code, though ... James -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
