linux-kernel - [RFC PATCH 1/2] blkdev.h: Introduce size_to

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Date:   Sun, 21 Apr 2019 00:53:27 -0300
From:   Marcos Paulo de Souza <marcos.souza.org@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Ming Lei <ming.lei@...hat.com>, Greg Edwards <gedwards@....com>,
        Hannes Reinecke <hare@...e.com>, linux-block@...r.kernel.org,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Jens Axboe <axboe@...nel.dk>,
        Bart Van Assche <bvanassche@....org>,
        Marcos Paulo de Souza <marcos.souza.org@...il.com>,
        Omar Sandoval <osandov@...com>,
        Damien Le Moal <damien.lemoal@....com>
Subject: [RFC PATCH 1/2] blkdev.h: Introduce size_to_sectors hlper function

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

Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@...il.com>
---
 include/linux/blkdev.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 317ab30d2904..7bf7b99161b7 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -871,6 +871,24 @@ static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
 #define SECTOR_SIZE (1 << SECTOR_SHIFT)
 #endif
 
+/**
+ * size_to_sectors - Convert size in bytes to number of sectors of 512 bytes
+ * @size: size in bytes to be converted to sectors
+ *
+ * Description:
+ * Kernel I/O operation 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. For example, for a capacity
+ * of 32M (33554432 bytes), the number of sectors will be 65536.
+ *
+ * Returns the number of sectors by the given number of bytes.
+ */
+static inline sector_t size_to_sectors(long long size)
+{
+	return size >> SECTOR_SHIFT;
+}
+
 /*
  * blk_rq_pos()			: the current sector
  * blk_rq_bytes()		: bytes left in the entire request
-- 
2.16.4