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From:   Marcos Paulo de Souza <marcos.souza.org@gmail.com>
To:     linux-block@vger.kernel.org
Cc:     Marcos Paulo de Souza <marcos.souza.org@gmail.com>,
        Jens Axboe <axboe@kernel.dk>, Hannes Reinecke <hare@suse.com>,
        Omar Sandoval <osandov@fb.com>, Ming Lei <ming.lei@redhat.com>,
        Damien Le Moal <damien.lemoal@wdc.com>,
        Bart Van Assche <bvanassche@acm.org>,
        Greg Edwards <gedwards@ddn.com>,
        linux-kernel@vger.kernel.org (open list)
Subject: [PATCH 1/2] blkdev.h: Introduce size_to_sectors hlper function
Date:   Mon, 29 Apr 2019 22:32:04 -0300
Message-Id: <20190430013205.1561708-2-marcos.souza.org@gmail.com>
In-Reply-To: <20190430013205.1561708-1-marcos.souza.org@gmail.com>
References: <20190430013205.1561708-1-marcos.souza.org@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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:
 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..f6cfe6970756 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
 
+/**
+ * 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 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 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