Re: [PATCH v3 3/3] mtd: block2mtd: Removes PAGE_MASK as a index to partition size

[Felix Fietkau]

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@xxxxxxxxx>
>> 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:
>> > > PAGE_MASK is no longer needed with the new term.
>> 
>> > This isn't too descriptive. What you probably mean is that we assume the
>> > erase size is always larger than PAGE_SIZE.
>> 
>> > > This patch keeps the device size aligned with the erase_size.
>> > >
>> > > Signed-off-by: Felix Fietkau <nbd@xxxxxxxxxxx>
>> > > Signed-off-by: Rodrigo Freire <rfreire@xxxxxxxxxx>
>> > > Signed-off-by: Herton Krzesinski <herton@xxxxxxxxxx>
>> > > ---
>> > > V3: Separated on a single patch
>> > > --- a/drivers/mtd/devices/block2mtd.c 2014-11-07 17:40:58.688747820 -0200
>> > > +++ b/drivers/mtd/devices/block2mtd.c 2014-11-07 17:41:28.054750893 -0200
>> > > @@ -291,8 +291,7 @@ static struct block2mtd_dev *add_device(
>> > > goto err_destroy_mutex;
>> > >
>> > > dev->mtd.name = name;
>> > > -
>> > > - 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.

- Felix
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