usb-storage: use max_hw_sectors instead of max_sectors

This patch (as1347) makes some adjustments to the way usb-storage
handles the request-queue parameters.

USB host controllers are able to handle arbitrarily long
scatter-gather lists, since they are limited only by main memory and
not by the controller hardware.  Hence the sg_tablesize field in the
host template can be increased to the maximum value.

Drivers like usb-storage aren't supposed to touch the queue's
max_sectors parameter; instead they are supposed to use the
max_hw_sectors value.  Accordingly, the patch replaces calls of
queue_max_sectors() with calls of queue_max_hw_sectors().  Oddly
enough, the blk_queue_max_sectors() routine is nevertheless still
appropriate.

The existing code imposes a limit of SCSI_DEFAULT_MAX_SECTORS (1024)
on the values accepted by the max_sectors attribute file.  There's no
reason not to accept larger values, so the limit is removed.  (It
would be nice to change the file's name to max_hw_sectors, but the old
name is already a well-established API.)

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

drivers/usb/storage/scsiglue.c

@@ -133,7 +133,7 @@ static int slave_configure(struct scsi_device *sdev)
 
 		if (us->fflags & US_FL_MAX_SECTORS_MIN)
 			max_sectors = PAGE_CACHE_SIZE >> 9;
-		if (queue_max_sectors(sdev->request_queue) > max_sectors)
+		if (queue_max_hw_sectors(sdev->request_queue) > max_sectors)
 			blk_queue_max_hw_sectors(sdev->request_queue,
 					      max_sectors);
 	} else if (sdev->type == TYPE_TAPE) {
@@ -484,7 +484,7 @@ static ssize_t show_max_sectors(struct device *dev, struct device_attribute *att
 {
 	struct scsi_device *sdev = to_scsi_device(dev);
 
-	return sprintf(buf, "%u\n", queue_max_sectors(sdev->request_queue));
+	return sprintf(buf, "%u\n", queue_max_hw_sectors(sdev->request_queue));
 }
 
 /* Input routine for the sysfs max_sectors file */
@@ -494,9 +494,9 @@ static ssize_t store_max_sectors(struct device *dev, struct device_attribute *at
 	struct scsi_device *sdev = to_scsi_device(dev);
 	unsigned short ms;
 
-	if (sscanf(buf, "%hu", &ms) > 0 && ms <= SCSI_DEFAULT_MAX_SECTORS) {
+	if (sscanf(buf, "%hu", &ms) > 0) {
 		blk_queue_max_hw_sectors(sdev->request_queue, ms);
-		return strlen(buf);
+		return count;
 	}
 	return -EINVAL;	
 }
@@ -539,7 +539,7 @@ struct scsi_host_template usb_stor_host_template = {
 	.slave_configure =		slave_configure,
 
 	/* lots of sg segments can be handled */
-	.sg_tablesize =			SG_ALL,
+	.sg_tablesize =			SCSI_MAX_SG_CHAIN_SEGMENTS,
 
 	/* limit the total size of a transfer to 120 KB */
 	.max_sectors =                  240,