linux-kernel - Re: introduce dm-snap-mv

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Date:	Thu, 7 Oct 2010 14:31:14 -0700
From:	Daniel Phillips <phillips@...nq.net>
To:	Cong Meng <mcpacino@...il.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@....de>, Nick Piggin <npiggin@...nel.dk>
Subject: Re: introduce dm-snap-mv

Hi Meng,

The patch looks sensible, however the question is: why do you want to
do this?  Would it not be better to generalize your metadata format to
accomodate the device's native blocksize?

Regards,

Daniel

> a kernel patch
> --------------
> Now, dm-snap-mv highly depends on a kernel patch below, which make __getblk()
> can get a 4K buffer head while block size of the disk is NOT 4K.
> 
> Signed-off-by: Cong Meng <mcpacino@...il.com>
> ---
>  fs/buffer.c |    7 ++-----
>  1 files changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 3e7dca2..f7f9d33 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1051,10 +1051,7 @@ grow_buffers(struct block_device *bdev, sector_t block, int size)
>  	pgoff_t index;
>  	int sizebits;
>  
> -	sizebits = -1;
> -	do {
> -		sizebits++;
> -	} while ((size << sizebits) < PAGE_SIZE);
> +	sizebits = PAGE_CACHE_SHIFT - bdev->bd_inode->i_blkbits;
>  
>  	index = block >> sizebits;
>  
> @@ -2924,7 +2921,7 @@ int submit_bh(int rw, struct buffer_head * bh)
>  	 */
>  	bio = bio_alloc(GFP_NOIO, 1);
>  
> -	bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
> +	bio->bi_sector = bh->b_blocknr << (bh->b_bdev->bd_inode->i_blkbits - 9);
>  	bio->bi_bdev = bh->b_bdev;
>  	bio->bi_io_vec[0].bv_page = bh->b_page;
>  	bio->bi_io_vec[0].bv_len = bh->b_size;
--
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