linux-kernel - Re: [PATCH v8 04/22] Change direct

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Date:	Thu, 31 Jul 2014 13:16:54 +0300
From:	Boaz Harrosh <openosd@...il.com>
To:	Matthew Wilcox <willy@...ux.intel.com>
CC:	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 04/22] Change direct_access calling convention

On 07/30/2014 11:34 PM, Matthew Wilcox wrote:
> On Wed, Jul 30, 2014 at 07:12:44PM +0300, Boaz Harrosh wrote:
>> 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.]
> 
> I considered a number of options here.  The VM wants things to be in pages.
> The filesystem wants things to be in block size.  The block device wants
> things to be in sectors.  It's all a mess when you try and converge.
> Everybody understands bytes.
> 
> Here's what I've come up with on top of patch 4/22.  Let me know what
> you think.
> 
> 
> diff --git a/arch/powerpc/sysdev/axonram.c b/arch/powerpc/sysdev/axonram.c
> index 3ee1c08..741293f 100644
> --- a/arch/powerpc/sysdev/axonram.c
> +++ b/arch/powerpc/sysdev/axonram.c
> @@ -146,11 +146,6 @@ axon_ram_direct_access(struct block_device *device, sector_t sector,
>  	struct axon_ram_bank *bank = device->bd_disk->private_data;
>  	loff_t offset = (loff_t)sector << AXON_RAM_SECTOR_SHIFT;
>  
> -	if (offset >= bank->size) {
> -		dev_err(&bank->device->dev, "Access outside of address space\n");
> -		return -ERANGE;
> -	}
> -
>  	*kaddr = (void *)(bank->ph_addr + offset);
>  	*pfn = virt_to_phys(*kaddr) >> PAGE_SHIFT;
>  
> diff --git a/drivers/block/brd.c b/drivers/block/brd.c
> index 33a39e7..3483458 100644
> --- a/drivers/block/brd.c
> +++ b/drivers/block/brd.c
> @@ -378,10 +378,6 @@ static long brd_direct_access(struct block_device *bdev, sector_t sector,
>  
>  	if (!brd)
>  		return -ENODEV;
> -	if (sector & (PAGE_SECTORS-1))
> -		return -EINVAL;
> -	if (sector + PAGE_SECTORS > get_capacity(bdev->bd_disk))
> -		return -ERANGE;
>  	page = brd_insert_page(brd, sector);
>  	if (!page)
>  		return -ENOSPC;
> diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c
> index 58958d1..2ee5556 100644
> --- a/drivers/s390/block/dcssblk.c
> +++ b/drivers/s390/block/dcssblk.c
> @@ -877,11 +877,7 @@ dcssblk_direct_access (struct block_device *bdev, sector_t secnum,
>  	if (!dev_info)
>  		return -ENODEV;
>  	dev_sz = dev_info->end - dev_info->start;
> -	if (secnum % (PAGE_SIZE/512))
> -		return -EINVAL;
>  	offset = secnum * 512;
> -	if (offset > dev_sz)
> -		return -ERANGE;
>  	*kaddr = (void *) (dev_info->start + offset);
>  	*pfn = virt_to_phys(*kaddr) >> PAGE_SHIFT;
>  
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index f1a158e..93ebdd53 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -450,8 +450,14 @@ long bdev_direct_access(struct block_device *bdev, sector_t sector,
>  	const struct block_device_operations *ops = bdev->bd_disk->fops;
>  	if (!ops->direct_access)
>  		return -EOPNOTSUPP;
> -	return ops->direct_access(bdev, sector + get_start_sect(bdev), addr,
> -					pfn, size);
> +	if ((sector + DIV_ROUND_UP(size, 512)) >
> +					part_nr_sects_read(bdev->bd_part))
> +		return -ERANGE;
> +	sector += get_start_sect(bdev);
> +	if (sector % (PAGE_SIZE / 512))
> +		return -EINVAL;
> +	size = ops->direct_access(bdev, sector, addr, pfn, size);
> +	return size ? size : -ERANGE;
>  }
>  EXPORT_SYMBOL_GPL(bdev_direct_access);
>  
> 

Very nice yes.

Only the check at ext2 I think is missing. Once you send the complete patch
I'll review it again. It would be very helpful if you send this patch a head
of Q, even for 3.17. It will help with merging later I think

Thanks
Boaz

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