[PATCH] sd.c: adjust READ_CAPACITY for broken devices

A number of USB mass storage devices return the wrong value in response to
READ CAPACITY: They give the total number of blocks rather than the
highest block number.  Currently the usb-storage driver tries to adjust
for this by altering the contents of the reply buffer.  That's not a very
good idea because it prevents users from seeing what the device actually
has to say; it violates the principle that a transport should do nothing
more than transfer data.

This patch moves the responsibility for adjusting the capacity to the sd
driver instead, by adding a new device flag.  After this has been merged
the corresponding change (to set the flag) will be made to the usb-storage
driver.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/sd.c

@@ -1104,6 +1104,11 @@ sd_read_capacity(struct scsi_disk *sdkp, char *diskname,
 			(buffer[9] << 16) | (buffer[10] << 8) | buffer[11];
 	}	
 
+	/* Some devices return the total number of sectors, not the
+	 * highest sector number.  Make the necessary adjustment. */
+	if (sdp->fix_capacity)
+		--sdkp->capacity;
+
 got_data:
 	if (sector_size == 0) {
 		sector_size = 512;

include/scsi/scsi_device.h

@@ -111,6 +111,7 @@ struct scsi_device {
 	unsigned allow_restart:1; /* issue START_UNIT in error handler */
 	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 int device_blocked;	/* Device returned QUEUE_FULL. */