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>

1 files changed, 15 insertions, 2 deletions

diff --git a/drivers/usb/storage/transport.c b/drivers/usb/storage/transport.c
index fcbbfdb7b2b..3523a0bfa0f 100644
--- a/drivers/usb/storage/transport.c
+++ b/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));