[PATCH v2 1/2] blkdev.h: Introduce bytes_to_sectors helper function

[PATCH v2 1/2] blkdev.h: Introduce bytes_to_sectors helper function

[Marcos Paulo de Souza]

This function takes an argument to specify the size of a block device,
in bytes, and return the number of sectors of 512 bytes.

Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
---
 Changes from v1:
 Rename size_to_sectors to bytes_to_sectors. (Martin K. Petersen)

 Changes from RFC:
 Reworked the documentation of size_to_sectors by removing a sentence that was
 explaining the size -> sectors math, which wasn't necessary given the
 description prior to the example. (suggested by Chaitanya)

 include/linux/blkdev.h | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 317ab30d2904..7ade2e24dbae 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -871,6 +871,23 @@ static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
 #define SECTOR_SIZE (1 << SECTOR_SHIFT)
 #endif
 
+/**
+ * bytes_to_sectors - Convert size in bytes to number of sectors of 512 bytes
+ * @bytes: number of bytes to be converted to sectors
+ *
+ * Description:
+ * Kernel I/O operations are always made in "sectors". In order to set the
+ * correct number of sectors for a given number of bytes, we need to group the
+ * number of bytes in "sectors of 512 bytes" by shifting the size value by 9,
+ * which is the same than dividing the size by 512.
+ *
+ * Returns the number of sectors by the given number of bytes.
+ */
+static inline sector_t bytes_to_sectors(long long bytes)
+{
+	return bytes >> SECTOR_SHIFT;
+}
+
 /*
  * blk_rq_pos()			: the current sector
  * blk_rq_bytes()		: bytes left in the entire request
-- 
2.16.4

[PATCH v2 2/2] null_blk: Make use of bytes_to_sectors helper

[Marcos Paulo de Souza]

This helper tries to make the code easier to read, and unifies the code
of returning the number of sectors for a given number of bytes.

Reviewed-by : Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>

---
 Changes from v1:
 Rename size_to_sectors to bytes_to_sectors. (Martin K. Petersen)

 drivers/block/null_blk_main.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/block/null_blk_main.c b/drivers/block/null_blk_main.c
index d7ac09c092f2..4c48f2a30941 100644
--- a/drivers/block/null_blk_main.c
+++ b/drivers/block/null_blk_main.c
@@ -853,7 +853,7 @@ static int null_flush_cache_page(struct nullb *nullb, struct nullb_page *c_page)
 	dst = kmap_atomic(t_page->page);
 
 	for (i = 0; i < PAGE_SECTORS;
-			i += (nullb->dev->blocksize >> SECTOR_SHIFT)) {
+			i += (bytes_to_sectors(nullb->dev->blocksize))) {
 		if (test_bit(i, c_page->bitmap)) {
 			offset = (i << SECTOR_SHIFT);
 			memcpy(dst + offset, src + offset,
@@ -957,7 +957,7 @@ static int copy_to_nullb(struct nullb *nullb, struct page *source,
 			null_free_sector(nullb, sector, true);
 
 		count += temp;
-		sector += temp >> SECTOR_SHIFT;
+		sector += bytes_to_sectors(temp);
 	}
 	return 0;
 }
@@ -989,7 +989,7 @@ static int copy_from_nullb(struct nullb *nullb, struct page *dest,
 		kunmap_atomic(dst);
 
 		count += temp;
-		sector += temp >> SECTOR_SHIFT;
+		sector += bytes_to_sectors(temp);
 	}
 	return 0;
 }
@@ -1004,7 +1004,7 @@ static void null_handle_discard(struct nullb *nullb, sector_t sector, size_t n)
 		null_free_sector(nullb, sector, false);
 		if (null_cache_active(nullb))
 			null_free_sector(nullb, sector, true);
-		sector += temp >> SECTOR_SHIFT;
+		sector += bytes_to_sectors(temp);
 		n -= temp;
 	}
 	spin_unlock_irq(&nullb->lock);
@@ -1074,7 +1074,7 @@ static int null_handle_rq(struct nullb_cmd *cmd)
 			spin_unlock_irq(&nullb->lock);
 			return err;
 		}
-		sector += len >> SECTOR_SHIFT;
+		sector += bytes_to_sectors(len);
 	}
 	spin_unlock_irq(&nullb->lock);
 
@@ -1109,7 +1109,7 @@ static int null_handle_bio(struct nullb_cmd *cmd)
 			spin_unlock_irq(&nullb->lock);
 			return err;
 		}
-		sector += len >> SECTOR_SHIFT;
+		sector += bytes_to_sectors(len);
 	}
 	spin_unlock_irq(&nullb->lock);
 	return 0;
@@ -1201,7 +1201,7 @@ static blk_status_t null_handle_cmd(struct nullb_cmd *cmd)
 		if (dev->queue_mode == NULL_Q_BIO) {
 			op = bio_op(cmd->bio);
 			sector = cmd->bio->bi_iter.bi_sector;
-			nr_sectors = cmd->bio->bi_iter.bi_size >> 9;
+			nr_sectors = bytes_to_sectors(cmd->bio->bi_iter.bi_size);
 		} else {
 			op = req_op(cmd->rq);
 			sector = blk_rq_pos(cmd->rq);
@@ -1406,7 +1406,7 @@ static void null_config_discard(struct nullb *nullb)
 		return;
 	nullb->q->limits.discard_granularity = nullb->dev->blocksize;
 	nullb->q->limits.discard_alignment = nullb->dev->blocksize;
-	blk_queue_max_discard_sectors(nullb->q, UINT_MAX >> 9);
+	blk_queue_max_discard_sectors(nullb->q, bytes_to_sectors(UINT_MAX));
 	blk_queue_flag_set(QUEUE_FLAG_DISCARD, nullb->q);
 }
 
@@ -1520,7 +1520,7 @@ static int null_gendisk_register(struct nullb *nullb)
 	if (!disk)
 		return -ENOMEM;
 	size = (sector_t)nullb->dev->size * 1024 * 1024ULL;
-	set_capacity(disk, size >> 9);
+	set_capacity(disk, bytes_to_sectors(size));
 
 	disk->flags |= GENHD_FL_EXT_DEVT | GENHD_FL_SUPPRESS_PARTITION_INFO;
 	disk->major		= null_major;
-- 
2.16.4