linux-kernel - [PATCH 3/5] brd: Add getgeo to block ops

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Date:	Wed, 27 Aug 2014 18:28:25 +0300
From:	Boaz Harrosh <boaz@...xistor.com>
To:	Jens Axboe <axboe@...com>, Matthew Wilcox <willy@...ux.intel.com>,
	Dmitry Monakhov <dmonakhov@...nvz.org>
CC:	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: [PATCH 3/5] brd: Add getgeo to block ops

From: Boaz Harrosh <boaz@...xistor.com>

Some programs like fdisk, require HDIO_GETGEO to work, which requires we
implement getgeo.

We set all hd_geometry members to 1, because this way fdisk
math will not try its crazy geometry math and get stuff totally wrong.

I was trying to get some values that will make fdisk Want to align
first sector on 4K (like 8, 16, 20, ... sectors) but nothing worked,
I searched the net the math is not your regular simple multiplication
at all.

If you managed to get these please tell me. I would love to solve
this.

But for now we use 4k physical sectors for fixing fdisk alignment
issues, and setting these here to something that will not make
fdisk serve us with crazy numbers.

Signed-off-by: Boaz Harrosh <boaz@...xistor.com>
---
 drivers/block/brd.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 78fe510..f841d9e 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -19,6 +19,7 @@
 #include <linux/radix-tree.h>
 #include <linux/fs.h>
 #include <linux/slab.h>
+#include <linux/hdreg.h>
 
 #include <asm/uaccess.h>
 
@@ -424,6 +425,23 @@ static int brd_ioctl(struct block_device *bdev, fmode_t mode,
 	return error;
 }
 
+static int brd_getgeo(struct block_device *bd, struct hd_geometry *geo)
+{
+	/* Just tell fdisk to get out of the way. The math here is so
+	 * convoluted and does not make any sense at all. With all 1s
+	 * The math just gets out of the way.
+	 * NOTE: I was trying to get some values that will make fdisk
+	 * Want to align first sector on 4K (like 8, 16, 20, ... sectors) but
+	 * nothing worked, I searched the net the math is not your regular
+	 * simple multiplication at all. If you managed to get these please
+	 * fix here. For now we use 4k physical sectors for this
+	 */
+	geo->heads = 1;
+	geo->sectors = 1;
+	geo->cylinders = 1;
+	return 0;
+}
+
 static const struct block_device_operations brd_fops = {
 	.owner =		THIS_MODULE,
 	.rw_page =		brd_rw_page,
@@ -431,6 +449,7 @@ static const struct block_device_operations brd_fops = {
 #ifdef CONFIG_BLK_DEV_XIP
 	.direct_access =	brd_direct_access,
 #endif
+	.getgeo =		brd_getgeo,
 };
 
 /*
-- 
1.9.3


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