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Date:	Wed, 30 Jul 2014 19:12:44 +0300
From:	Boaz Harrosh <openosd@...il.com>
To:	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
CC:	willy@...ux.intel.com
Subject: Re: [PATCH v8 04/22] Change direct_access calling convention

On 07/30/2014 07:03 PM, Boaz Harrosh wrote:
<>
>> +long bdev_direct_access(struct block_device *bdev, sector_t sector,
>> +			void **addr, unsigned long *pfn, long size)
>> +{
>> +	const struct block_device_operations *ops = bdev->bd_disk->fops;
>> +	if (!ops->direct_access)
>> +		return -EOPNOTSUPP;
> 
> You need to check alignment on PAGE_SIZE since this API requires it, do
> to pfn defined to a page_number.
> 
> (Unless you want to define another output-param like page_offset.
>  but this exercise can be left to the caller)
> 
> You also need to check against the partition boundary. so something like:
> 
> + 	if (sector & (PAGE_SECTORS-1))
> + 		return -EINVAL;
> +	if (unlikely(sector + size > part_nr_sects_read(bdev->bd_part)))

Off course I was wrong here size is in bytes not in sectors. Which points
out that maybe this API needs to be in sectors.

[Actually it needs to be in pages both size and offset, because of return of
pfn, but its your call.]

Anyway my code above needs to be fixed with
	(size + 512 -1) / 512

Thanks
Boaz

> + 		return -ERANGE;
> 
> Then perhaps you can remove that check from drivers
> 
>> +	return ops->direct_access(bdev, sector + get_start_sect(bdev), addr,
>> +					pfn, size);
>> +}
>> +EXPORT_SYMBOL_GPL(bdev_direct_access);
<>


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