Re: [Bug 12207] block reads/writes > 122880 bytes to USB tape drive gives EBUSY

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Tue, 2008-12-23 at 08:55 -0600, James Bottomley wrote:
> > ------- Comment #6 from stern@rowland.harvard.edu  2008-12-23 05:59 -------
> > You can change the max_sectors setting through sysfs.  However the last time I
> > looked, the block layer limited max_sectors to 512 KB or something on that
> > order, so you can't get too much improvement.
> > 
> > Why is a limit of 120 KB unreasonably small?  All it means is that you have to
> > use more system calls to transfer the same amount of data.  Is anything wrong
> > with that?
> 
> Tapes need large block sizes.
> 
> We can accommodate both:  Just check for TYPE_TAPE in the
> slave_configure() and bump the limit back up.  Any USB tape that doesn't
> do large block transfers will be truly broken.

Following up on this, does this fix it?

I notice that Linus was the one who actually committed this change in
2.6.0-test10, so it's been in the entire 2.6 release.

James

---

diff --git a/drivers/usb/storage/scsiglue.c b/drivers/usb/storage/scsiglue.c
index 09779f6..ae4b01c 100644
--- a/drivers/usb/storage/scsiglue.c
+++ b/drivers/usb/storage/scsiglue.c
@@ -127,7 +127,12 @@ static int slave_configure(struct scsi_device *sdev)
 		if (sdev->request_queue->max_sectors > max_sectors)
 			blk_queue_max_sectors(sdev->request_queue,
 					      max_sectors);
-	}
+	} else if (sdev->type == TYPE_TAPE)
+		/* Tapes need much higher max sector transfers, so just
+		 * raise it to the maximum possible and let the queue
+		 * segment size sort out the real limit
+		 */
+		blk_queue_max_sectors(sdev->request_queue, 0xFFFF);
 
 	/* We can't put these settings in slave_alloc() because that gets
 	 * called before the device type is known.  Consequently these