Re: [PATCH 6/9] btrfs: calculate end of bio offset properly

[Omar Sandoval <osandov@osandov.com>]

On Wed, Nov 16, 2016 at 01:52:13PM +0100, Christoph Hellwig wrote:
> Use the bvec offset and len members to prepare for multipage bvecs.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/btrfs/compression.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
> index 8618ac3..27e9feb 100644
> --- a/fs/btrfs/compression.c
> +++ b/fs/btrfs/compression.c
> @@ -445,6 +445,13 @@ int btrfs_submit_compressed_write(struct inode *inode, u64 start,
>  	return 0;
>  }
>  
> +static u64 bio_end_offset(struct bio *bio)
> +{
> +	struct bio_vec *last = &bio->bi_io_vec[bio->bi_vcnt - 1];
> +
> +	return page_offset(last->bv_page) + last->bv_len - last->bv_offset;

Why is this minus bv_offset and not plus? Am I misunderstanding
bv_offset?

> +}
> +
>  static noinline int add_ra_bio_pages(struct inode *inode,
>  				     u64 compressed_end,
>  				     struct compressed_bio *cb)
> @@ -463,8 +470,7 @@ static noinline int add_ra_bio_pages(struct inode *inode,
>  	u64 end;
>  	int misses = 0;
>  
> -	page = cb->orig_bio->bi_io_vec[cb->orig_bio->bi_vcnt - 1].bv_page;
> -	last_offset = (page_offset(page) + PAGE_SIZE);
> +	last_offset = bio_end_offset(cb->orig_bio);
>  	em_tree = &BTRFS_I(inode)->extent_tree;
>  	tree = &BTRFS_I(inode)->io_tree;
>  
> -- 
> 2.1.4
> 
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-- 
Omar