USB Storage: indistinguishable devices with broken and unbroken firmware

there's a USB mass storage device which exists in two version. One
reports the correct size and the other does not. Apart from that they
are identical and cannot be told apart. Here's a heuristic based on the
empirical finding that drives have even sizes.


Signed-off-by: Oliver Neukum <oneukum@suse.de>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Matthew Dharm <mdharm-usb@one-eyed-alien.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/scsi/sd.c

@@ -1269,9 +1269,18 @@ sd_read_capacity(struct scsi_disk *sdkp, char *diskname,
 
 	/* Some devices return the total number of sectors, not the
 	 * highest sector number.  Make the necessary adjustment. */
-	if (sdp->fix_capacity)
+	if (sdp->fix_capacity) {
 		--sdkp->capacity;
 
+	/* Some devices have version which report the correct sizes
+	 * and others which do not. We guess size according to a heuristic
+	 * and err on the side of lowering the capacity. */
+	} else {
+		if (sdp->guess_capacity)
+			if (sdkp->capacity & 0x01) /* odd sizes are odd */
+				--sdkp->capacity;
+	}
+
 got_data:
 	if (sector_size == 0) {
 		sector_size = 512;

drivers/usb/storage/scsiglue.c

@@ -153,6 +153,12 @@ static int slave_configure(struct scsi_device *sdev)
 		if (us->flags & US_FL_FIX_CAPACITY)
 			sdev->fix_capacity = 1;
 
+		/* A few disks have two indistinguishable version, one of
+		 * which reports the correct capacity and the other does not.
+		 * The sd driver has to guess which is the case. */
+		if (us->flags & US_FL_CAPACITY_HEURISTICS)
+			sdev->guess_capacity = 1;
+
 		/* Some devices report a SCSI revision level above 2 but are
 		 * unable to handle the REPORT LUNS command (for which
 		 * support is mandatory at level 3).  Since we already have

drivers/usb/storage/unusual_devs.h

@@ -1434,7 +1434,7 @@ UNUSUAL_DEV(  0xed06, 0x4500, 0x0001, 0x0001,
 		"DataStor",
 		"USB4500 FW1.04",
 		US_SC_DEVICE, US_PR_DEVICE, NULL,
-		US_FL_FIX_CAPACITY),
+		US_FL_CAPACITY_HEURISTICS),
 
 /* Control/Bulk transport for all SubClass values */
 USUAL_DEV(US_SC_RBC, US_PR_CB, USB_US_TYPE_STOR),

include/linux/usb_usual.h

@@ -46,7 +46,9 @@
 	US_FLAG(MAX_SECTORS_64,	0x00000400)			\
 		/* Sets max_sectors to 64    */			\
 	US_FLAG(IGNORE_DEVICE,	0x00000800)			\
-		/* Don't claim device */
+		/* Don't claim device */			\
+	US_FLAG(CAPACITY_HEURISTICS,	0x00001000)		\
+		/* sometimes sizes is too big */
 
 #define US_FLAG(name, value)	US_FL_##name = value ,
 enum { US_DO_ALL_FLAGS };

include/scsi/scsi_device.h

@@ -122,6 +122,7 @@ struct scsi_device {
 	unsigned no_uld_attach:1; /* disable connecting to upper level drivers */
 	unsigned select_no_atn:1;
 	unsigned fix_capacity:1;	/* READ_CAPACITY is too high by 1 */
+	unsigned guess_capacity:1;	/* READ_CAPACITY might be too high by 1 */
 	unsigned retry_hwerror:1;	/* Retry HARDWARE_ERROR */
 
 	unsigned int device_blocked;	/* Device returned QUEUE_FULL. */