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Commit 49d6271b authored by Alan Stern's avatar Alan Stern Committed by Greg Kroah-Hartman
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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: default avatarAlan Stern <stern@rowland.harvard.edu>
CC: Matthew Dharm <mdharm-usb@one-eyed-alien.net>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent efe7daf2

drivers/usb/storage/scsiglue.c

+5 −5
Original line number Diff line number Diff line
@@ -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,