usb-storage: automatically recognize bad residues

This patch (as1119) will help to reduce the clutter of usb-storage's
unusual_devs file by automatically detecting some devices that need
the IGNORE_RESIDUE flag.  The idea is that devices should never return
a non-zero residue for an INQUIRY or a READ CAPACITY command unless
they failed to transfer all the requested data.  So if one of these
commands transfers a standard amount of data but there is a positive
residue, we know that the residue is bogus and we can set the flag.

This fixes the problems reported in Bugzilla #11125.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/storage/transport.c

@@ -1032,8 +1032,21 @@ int usb_stor_Bulk_transport(struct scsi_cmnd *srb, struct us_data *us)
 
 	/* try to compute the actual residue, based on how much data
 	 * was really transferred and what the device tells us */
-	if (residue) {
-		if (!(us->fflags & US_FL_IGNORE_RESIDUE)) {
+	if (residue && !(us->fflags & US_FL_IGNORE_RESIDUE)) {
+
+		/* Heuristically detect devices that generate bogus residues
+		 * by seeing what happens with INQUIRY and READ CAPACITY
+		 * commands.
+		 */
+		if (bcs->Status == US_BULK_STAT_OK &&
+				scsi_get_resid(srb) == 0 &&
+					((srb->cmnd[0] == INQUIRY &&
+						transfer_length == 36) ||
+					(srb->cmnd[0] == READ_CAPACITY &&
+						transfer_length == 8))) {
+			us->fflags |= US_FL_IGNORE_RESIDUE;
+
+		} else {
 			residue = min(residue, transfer_length);
 			scsi_set_resid(srb, max(scsi_get_resid(srb),
 			                                       (int) residue));