Re: [PATCH 04/26] buffer: Add get_nth_bh()

On Tue, Sep 19, 2023 at 4:20 PM Matthew Wilcox (Oracle) wrote:
>
> Extract this useful helper from nilfs_page_get_nth_block()
>
> Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
> ---
>  fs/nilfs2/page.h            |  7 +------
>  include/linux/buffer_head.h | 22 ++++++++++++++++++++++
>  2 files changed, 23 insertions(+), 6 deletions(-)
>
> diff --git a/fs/nilfs2/page.h b/fs/nilfs2/page.h
> index 21ddcdd4d63e..344d71942d36 100644
> --- a/fs/nilfs2/page.h
> +++ b/fs/nilfs2/page.h
> @@ -55,12 +55,7 @@ unsigned long nilfs_find_uncommitted_extent(struct inode *inode,
>  static inline struct buffer_head *
>  nilfs_page_get_nth_block(struct page *page, unsigned int count)
>  {
> -       struct buffer_head *bh = page_buffers(page);
> -
> -       while (count-- > 0)
> -               bh = bh->b_this_page;
> -       get_bh(bh);
> -       return bh;
> +       return get_nth_bh(page_buffers(page), count);
>  }
>
>  #endif /* _NILFS_PAGE_H */
> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> index 1001244a8941..9fc615ee17fd 100644
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -457,6 +457,28 @@ __bread(struct block_device *bdev, sector_t block, unsigned size)
>         return __bread_gfp(bdev, block, size, __GFP_MOVABLE);
>  }
>
> +/**
> + * get_nth_bh - Get a reference on the n'th buffer after this one.
> + * @bh: The buffer to start counting from.
> + * @count: How many buffers to skip.
> + *
> + * This is primarily useful for finding the nth buffer in a folio; in
> + * that case you pass the head buffer and the byte offset in the folio
> + * divided by the block size.  It can be used for other purposes, but
> + * it will wrap at the end of the folio rather than returning NULL or
> + * proceeding to the next folio for you.
> + *
> + * Return: The requested buffer with an elevated refcount.
> + */
> +static inline struct buffer_head *get_nth_bh(struct buffer_head *bh,
> +               unsigned int count)
> +{
> +       while (count--)
> +               bh = bh->b_this_page;
> +       get_bh(bh);
> +       return bh;
> +}
> +
>  bool block_dirty_folio(struct address_space *mapping, struct folio *folio);
>
>  #ifdef CONFIG_BUFFER_HEAD
> --
> 2.40.1
>

Acked-by: Ryusuke Konishi <[email protected]>

Looks good to me.

Thanks,
Ryusuke Konishi