block: add blk_queue_update_dma_pad

This adds blk_queue_update_dma_pad to prevent LLDs from overwriting
the dma pad mask wrongly (we added blk_queue_update_dma_alignment due
to the same reason).

This also converts libata to use blk_queue_update_dma_pad instead of
blk_queue_dma_pad.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/blk-settings.c

@@ -302,18 +302,34 @@ EXPORT_SYMBOL(blk_queue_stack_limits);
  * @q:     the request queue for the device
  * @mask:  pad mask
  *
- * Set pad mask.  Direct IO requests are padded to the mask specified.
+ * Set dma pad mask.
  *
- * Appending pad buffer to a request modifies ->data_len such that it
- * includes the pad buffer.  The original requested data length can be
- * obtained using blk_rq_raw_data_len().
+ * Appending pad buffer to a request modifies the last entry of a
+ * scatter list such that it includes the pad buffer.
  **/
 void blk_queue_dma_pad(struct request_queue *q, unsigned int mask)
 {
 	q->dma_pad_mask = mask;
 }
 EXPORT_SYMBOL(blk_queue_dma_pad);
 
+/**
+ * blk_queue_update_dma_pad - update pad mask
+ * @q:     the request queue for the device
+ * @mask:  pad mask
+ *
+ * Update dma pad mask.
+ *
+ * Appending pad buffer to a request modifies the last entry of a
+ * scatter list such that it includes the pad buffer.
+ **/
+void blk_queue_update_dma_pad(struct request_queue *q, unsigned int mask)
+{
+	if (mask > q->dma_pad_mask)
+		q->dma_pad_mask = mask;
+}
+EXPORT_SYMBOL(blk_queue_update_dma_pad);
+
 /**
  * blk_queue_dma_drain - Set up a drain buffer for excess dma.
  * @q:  the request queue for the device

drivers/ata/libata-scsi.c

@@ -885,7 +885,8 @@ static int ata_scsi_dev_config(struct scsi_device *sdev,
 		/* set the min alignment and padding */
 		blk_queue_update_dma_alignment(sdev->request_queue,
 					       ATA_DMA_PAD_SZ - 1);
-		blk_queue_dma_pad(sdev->request_queue, ATA_DMA_PAD_SZ - 1);
+		blk_queue_update_dma_pad(sdev->request_queue,
+					 ATA_DMA_PAD_SZ - 1);
 
 		/* configure draining */
 		buf = kmalloc(ATAPI_MAX_DRAIN, q->bounce_gfp | GFP_KERNEL);

include/linux/blkdev.h

@@ -776,6 +776,7 @@ extern void blk_queue_max_segment_size(struct request_queue *, unsigned int);
 extern void blk_queue_hardsect_size(struct request_queue *, unsigned short);
 extern void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b);
 extern void blk_queue_dma_pad(struct request_queue *, unsigned int);
+extern void blk_queue_update_dma_pad(struct request_queue *, unsigned int);
 extern int blk_queue_dma_drain(struct request_queue *q,
 			       dma_drain_needed_fn *dma_drain_needed,
 			       void *buf, unsigned int size);