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

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Message-ID: <20140827175327.GF3285@linux.intel.com>
Date:	Wed, 27 Aug 2014 13:53:27 -0400
From:	Matthew Wilcox <willy@...ux.intel.com>
To:	Boaz Harrosh <boaz@...xistor.com>
Cc:	Jens Axboe <axboe@...com>, Dmitry Monakhov <dmonakhov@...nvz.org>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 3/5] brd: Add getgeo to block ops

On Wed, Aug 27, 2014 at 06:28:25PM +0300, Boaz Harrosh wrote:
> 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.

Are you saying that fdisk ignores the 4k physical sectors (that you set up
in patch 5/5) in favour of the geometry exposed here?  That doesn't make
sense to me, since it would misalign 4k-physical ATA drives if it did.

I don't see anywhere else in the kernel reporting (1,1,1).  The most common
form to fake a geometry uses (64, 32, x), including SCSI.
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