sd: Limit transfer length

Until now the per-command transfer length has exclusively been gated by
the max_sectors parameter in the scsi_host template. Given that the size
of this parameter has been bumped to an unsigned int we have to be
careful not to exceed the target device's capabilities.

If the if the device specifies a Maximum Transfer Length in the Block
Limits VPD we'll use that value. Otherwise we'll use 0xffffffff for
devices that have use_16_for_rw set and 0xffff for the rest. We then
combine the chosen disk limit with max_sectors in the host template. The
smaller of the two will be used to set the max_hw_sectors queue limit.

Signed-off-by: Martin K. Petersen <[e-mail]>
Reviewed-by: Ewan D. Milne <[e-mail]>
Signed-off-by: Christoph Hellwig <[e-mail]>

drivers/scsi/sd.c

···
 		}
 	}
 
-	sdp->use_16_for_rw = (sdkp->capacity > 0xffffffff);
+	if (sdkp->capacity > 0xffffffff) {
+		sdp->use_16_for_rw = 1;
+		sdkp->max_xfer_blocks = SD_MAX_XFER_BLOCKS;
+	} else
+		sdkp->max_xfer_blocks = SD_DEF_XFER_BLOCKS;
 
 	/* Rescale capacity to 512-byte units */
 	if (sector_size == 4096)
···
 {
 	unsigned int sector_sz = sdkp->device->sector_size;
 	const int vpd_len = 64;
+	u32 max_xfer_length;
 	unsigned char *buffer = kmalloc(vpd_len, GFP_KERNEL);
 
 	if (!buffer ||
 	    /* Block Limits VPD */
 	    scsi_get_vpd_page(sdkp->device, 0xb0, buffer, vpd_len))
 		goto out;
+
+	max_xfer_length = get_unaligned_be32(&buffer[8]);
+	if (max_xfer_length)
+		sdkp->max_xfer_blocks = max_xfer_length;
 
 	blk_queue_io_min(sdkp->disk->queue,
 			 get_unaligned_be16(&buffer[6]) * sector_sz);
···
 	struct scsi_disk *sdkp = scsi_disk(disk);
 	struct scsi_device *sdp = sdkp->device;
 	unsigned char *buffer;
+	unsigned int max_xfer;
 
 	SCSI_LOG_HLQUEUE(3, sd_printk(KERN_INFO, sdkp,
 				      "sd_revalidate_disk\n"));
···
 	 */
 	sd_set_flush_flag(sdkp);
 
+	max_xfer = min_not_zero(queue_max_hw_sectors(sdkp->disk->queue),
+				sdkp->max_xfer_blocks);
+	max_xfer <<= ilog2(sdp->sector_size) - 9;
+	blk_queue_max_hw_sectors(sdkp->disk->queue, max_xfer);
 	set_capacity(disk, sdkp->capacity);
 	sd_config_write_same(sdkp);
 	kfree(buffer);

drivers/scsi/sd.h

···
 };
 
 enum {
+	SD_DEF_XFER_BLOCKS = 0xffff,
+	SD_MAX_XFER_BLOCKS = 0xffffffff,
 	SD_MAX_WS10_BLOCKS = 0xffff,
 	SD_MAX_WS16_BLOCKS = 0x7fffff,
 };
···
 	struct gendisk	*disk;
 	atomic_t	openers;
 	sector_t	capacity;	/* size in 512-byte sectors */
+	u32		max_xfer_blocks;
 	u32		max_ws_blocks;
 	u32		max_unmap_blocks;
 	u32		unmap_granularity;