Re: [PATCH v2] btrfs: Return right extent when fiemap gives unaligned offset and len.

[Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>]

Hi Qu,

(2014/07/25 10:49), Qu Wenruo wrote:
> When page aligned start and len passed to extent_fiemap(), the result is
> good, but when start and len is not aligned, e.g. start = 1 and len =
> 4095 is passed to extent_fiemap(), it returns no extent.
> 
> The problem is that start and len is all rounded up which causes the
> problem. This patch will round down start and round up (start + len) to
> return right extent.
> 
> Reported-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
> ---
> changelog:
> v2: reword the description(ALIGN rounds up, not rounds down).
> ---
>   fs/btrfs/extent_io.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index a389820..1c70cff 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -4213,8 +4213,8 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
>   		return -ENOMEM;
>   	path->leave_spinning = 1;
>   
> -	start = ALIGN(start, BTRFS_I(inode)->root->sectorsize);
> -	len = ALIGN(len, BTRFS_I(inode)->root->sectorsize);
> +	start = round_down(start, BTRFS_I(inode)->root->sectorsize);
> +	len = round_up(max, BTRFS_I(inode)->root->sectorsize) - start;

I have one question.

Why isn't it "len = round_up(len, BTRFS_I(inode)->root->sectorsize);" ?
Old behavior make len sectorsize aligned. However, if start is not
aligned to sectorsize, new bahavior make len not sectorsize aligned.
Does it an expected behavior?

CMIIW. I'm not good at extent code.

Thanks,
Satoru

>   
>   	/*
>   	 * lookup the last file extent.  We're not using i_size here
>