On Mon, 25 Aug 2014, Alan Stern wrote: > On Mon, 25 Aug 2014, James Bottomley wrote: > > > 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. > > Heh. The change was made by commit 4d7db04a7a69 ([SCSI] add > SCSI_UNKNOWN and LUN transfer limit restrictions) back in 2006 -- the > 2.6.17 kernel. If nobody has complained in all this time then it's > probably not worth changing. It turns out the code is already there, and I didn't realize because I was looking at the wrong source file. scsi_sysfs_device_initialize() already does: sdev->scsi_level = starget->scsi_level; Here's the update to the patch, adding an appropriate comment and setting the new sdev->lun_in_sdb flag properly: Alan Stern Index: usb-3.16/drivers/scsi/scsi_sysfs.c =================================================================== --- usb-3.16.orig/drivers/scsi/scsi_sysfs.c +++ usb-3.16/drivers/scsi/scsi_sysfs.c @@ -1238,7 +1238,19 @@ void scsi_sysfs_device_initialize(struct sdev->sdev_dev.class = &sdev_class; dev_set_name(&sdev->sdev_dev, "%d:%d:%d:%d", sdev->host->host_no, sdev->channel, sdev->id, sdev->lun); + /* + * Get a default scsi_level from the target (derived from sibling + * devices). This is the best we can do for guessing how to set + * sdev->lun_in_cdb for the initial INQUIRY command. For LUN 0 the + * setting doesn't matter, because all the bits are zero anyway. + * But it does matter for higher LUNs. + */ sdev->scsi_level = starget->scsi_level; + if (sdev->scsi_level <= SCSI_2 && + sdev->scsi_level != SCSI_UNKNOWN && + !shost->no_scsi2_lun_in_cdb) + sdev->lun_in_cdb = 1; + transport_setup_device(&sdev->sdev_gendev); spin_lock_irqsave(shost->host_lock, flags); list_add_tail(&sdev->same_target_siblings, &starget->devices); -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
