[Bug 80711] [PATCH]SG_FLAG_LUN_INHIBIT is no longer implemented and there's not way to prevent the kernel from using the 2nd cdb byte for the LUN

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https://bugzilla.kernel.org/show_bug.cgi?id=80711

--- Comment #12 from Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> ---
On Thu, 21 Aug 2014, Christoph Hellwig wrote:

> On Thu, Aug 21, 2014 at 10:41:02AM -0400, Douglas Gilbert wrote:
> > Perhaps we could add another bit flag in struct
> > scsi_host_template such as:
> >     unsigned int transport_says_dont_scsi2_lun_cmd:1;
> > 
> > then drivers/usb/storage/scsiglue.c could set that
> > bit in its usb_stor_host_template and
> > drivers/scsi/scsi.c could take heed (and not mask
> > cmd->cmnd[1] with the LUN).
> 
> Fully agreed.
> 
> (except that I'd shorten the flag name to .no_scsi2lun :))

Okay, here's a patch that implements the suggestion, except that I put
the flag in the Scsi_Host structure instead of the template.  This was
to minimize the impact of the change.  Among the various SCSI-over-USB
transports, only the Bulk-Only transport gives the LUN separately from
the CDB.  I don't know if there are any multi-LUN USB devices that
don't use the Bulk-Only transport, but if there are then they won't 
work if the LUN isn't stored in CDB[1].

Tiziano, does this do what you want?

Alan Stern



Index: usb-3.16/include/scsi/scsi_host.h
===================================================================
--- usb-3.16.orig/include/scsi/scsi_host.h
+++ usb-3.16/include/scsi/scsi_host.h
@@ -695,6 +695,9 @@ struct Scsi_Host {
     /* The controller does not support WRITE SAME */
     unsigned no_write_same:1;

+    /* The transport requires the LUN bits NOT to be stored in CDB[1] */
+    unsigned no_scsi2_lun:1;
+
     /*
      * Optional work queue to be utilized by the transport
      */
Index: usb-3.16/drivers/scsi/scsi.c
===================================================================
--- usb-3.16.orig/drivers/scsi/scsi.c
+++ usb-3.16/drivers/scsi/scsi.c
@@ -678,7 +678,8 @@ int scsi_dispatch_cmd(struct scsi_cmnd *
      * If SCSI-2 or lower, store the LUN value in cmnd.
      */
     if (cmd->device->scsi_level <= SCSI_2 &&
-        cmd->device->scsi_level != SCSI_UNKNOWN) {
+        cmd->device->scsi_level != SCSI_UNKNOWN &&
+        !host->no_scsi2_lun) {
         cmd->cmnd[1] = (cmd->cmnd[1] & 0x1f) |
                    (cmd->device->lun << 5 & 0xe0);
     }
Index: usb-3.16/drivers/usb/storage/usb.c
===================================================================
--- usb-3.16.orig/drivers/usb/storage/usb.c
+++ usb-3.16/drivers/usb/storage/usb.c
@@ -981,6 +981,14 @@ int usb_stor_probe2(struct us_data *us)
     if (!(us->fflags & US_FL_SCM_MULT_TARG))
         us_to_host(us)->max_id = 1;

+    /*
+     * Like Windows, we won't store the LUN bits in CDB[1] for SCSI-2
+     * devices using the Bulk-Only transport (even though this violates
+     * the SCSI spec).
+     */
+    if (us->transport == usb_stor_Bulk_transport)
+        us_to_host(us)->no_scsi2_lun = 1;
+
     /* Find the endpoints and calculate pipe values */
     result = get_pipes(us);
     if (result)

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