linux-kernel - Re: [PATCH v3 3/3] mtd: block2mtd: Removes PAGE

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Date:	Tue, 24 Feb 2015 21:30:21 +1300
From:	Felix Fietkau <nbd@...nwrt.org>
To:	Brian Norris <computersforpeace@...il.com>
CC:	Rodrigo Freire <rfreire@...hat.com>, linux-mtd@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Jörn Engel <joern@...fs.org>,
	dwmw2@...radead.org, Herton Krzesinski <hkrzesin@...hat.com>
Subject: Re: [PATCH v3 3/3] mtd: block2mtd: Removes PAGE_MASK as a index to
 partition size

On 2015-02-24 21:27, Brian Norris wrote:
> On Tue, Feb 24, 2015 at 09:20:31PM +1300, Felix Fietkau wrote:
>> On 2015-02-24 21:07, Brian Norris wrote:
>> > On Wed, Nov 26, 2014 at 08:19:32AM -0500, Rodrigo Freire wrote:
>> >> From: "Brian Norris" <computersforpeace@...il.com>
>> >> Sent: Wednesday, November 26, 2014 5:21:47 AM
>> >> Subject: Re: [PATCH v3 3/3] mtd: block2mtd: Removes PAGE_MASK as a index to
>> >> partition size
>> >> 
>> >> > On Sun, Nov 09, 2014 at 07:23:12AM -0500, Rodrigo Freire wrote:
>> >> > > - dev->mtd.size = dev->blkdev->bd_inode->i_size & PAGE_MASK;
>> >> > > + dev->mtd.size = dev->blkdev->bd_inode->i_size & ~(erase_size - 1);
>> >> 
>> >> > You never guaranteed that erase_size is a power of two, so this doesn't
>> >> > necessarily mask the way you'd like...
>> >> 
>> >> > But also, why is this even necessary? I see that we should already have
>> >> > errored out if this was actually significant, since we have above:
>> >> 
>> >> > if ((long)dev->blkdev->bd_inode->i_size % erase_size) {
>> >> > pr_err("erasesize must be a divisor of device size\n");
>> >> > goto err_free_block2mtd;
>> >> > }
>> >> 
>> >> Hello Brian, and thanks for the review.
>> >> 
>> >> Honestly, I'd leave that untouched, but Jörn pointed that it could be a issue at https://lkml.org/lkml/2014/9/9/680
>> >> 
>> >> I'd happily let it go without this patch 3, unless Jörg wants to state otherwise.
>> > 
>> > OK let's drop this patch from the series. At best, we could just do
>> > something like this instead:
>> > 
>> > -	dev->mtd.size = dev->blkdev->bd_inode->i_size & PAGE_MASK;
>> > +	dev->mtd.size = dev->blkdev->bd_inode->i_size;
>> > 
>> > But that's really just an unnecessary change.
>> If I remember correctly, it was problematic to have a dev->mtd.size
>> value which is not a multiple of the erase size. I think that was the
>> reason for patch 3.
> 
> The what's this for?
> 
> 	if ((long)dev->blkdev->bd_inode->i_size % erase_size) {
> 		pr_err("erasesize must be a divisor of device size\n");
> 		goto err_free_block2mtd;
> 	}
I think we should just trim the mtd size to a multiple of erase size and
remove this check. It is a bit impractical for many cases.

- Felix
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