Re: [PATCH 10/14] iomap: lift the xfs writeback code to iomap

[Darrick J. Wong]

On Thu, Oct 17, 2019 at 07:56:20PM +0200, Christoph Hellwig wrote:
> Take the xfs writeback code and move it to fs/iomap.  A new structure
> with three methods is added as the abstraction from the generic writeback
> code to the file system.  These methods are used to map blocks, submit an
> ioend, and cancel a page that encountered an error before it was added to
> an ioend.
> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>

<snip>

> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 24bd227d59f9..71fd12ee5616 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -4,6 +4,7 @@
>  
>  #include <linux/atomic.h>
>  #include <linux/bitmap.h>
> +#include <linux/blk_types.h>
>  #include <linux/mm.h>
>  #include <linux/types.h>
>  #include <linux/mm_types.h>
> @@ -12,6 +13,7 @@
>  struct address_space;
>  struct fiemap_extent_info;
>  struct inode;
> +struct iomap_writepage_ctx;
>  struct iov_iter;
>  struct kiocb;
>  struct page;
> @@ -185,6 +187,63 @@ loff_t iomap_seek_data(struct inode *inode, loff_t offset,
>  sector_t iomap_bmap(struct address_space *mapping, sector_t bno,
>  		const struct iomap_ops *ops);
>  
> +/*
> + * Structure for writeback I/O completions.
> + */
> +struct iomap_ioend {
> +	struct list_head	io_list;	/* next ioend in chain */
> +	u16			io_type;
> +	u16			io_flags;	/* IOMAP_F_* */
> +	struct inode		*io_inode;	/* file being written to */
> +	size_t			io_size;	/* size of the extent */
> +	loff_t			io_offset;	/* offset in the file */
> +	void			*io_private;	/* file system private data */
> +	struct bio		*io_bio;	/* bio being built */
> +	struct bio		io_inline_bio;	/* MUST BE LAST! */
> +};
> +
> +struct iomap_writeback_ops {
> +	/*
> +	 * Required, maps the blocks so that writeback can be performed on
> +	 * the range starting at offset.
> +	 */
> +	int (*map_blocks)(struct iomap_writepage_ctx *wpc, struct inode *inode,
> +				loff_t offset);
> +
> +	/*
> +	 * Optional, allows the file systems to perform actions just before
> +	 * submitting the bio and/or override the bio end_io handler for complex
> +	 * operations like copy on write extent manipulation or unwritten extent
> +	 * conversions.
> +	 */
> +	int (*submit_ioend)(struct iomap_ioend *ioend, int status);
> +

Looks ok, but I reserve the right to rename this to ->prepare_ioend() or
something. :)

Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>

--D

> +	/*
> +	 * Optional, allows the file system to discard state on a page where
> +	 * we failed to submit any I/O.
> +	 */
> +	void (*discard_page)(struct page *page);
> +};
> +
> +struct iomap_writepage_ctx {
> +	struct iomap		iomap;
> +	struct iomap_ioend	*ioend;
> +	const struct iomap_writeback_ops *ops;
> +};
> +
> +void iomap_finish_ioends(struct iomap_ioend *ioend, int error);
> +void iomap_ioend_try_merge(struct iomap_ioend *ioend,
> +		struct list_head *more_ioends,
> +		void (*merge_private)(struct iomap_ioend *ioend,
> +				struct iomap_ioend *next));
> +void iomap_sort_ioends(struct list_head *ioend_list);
> +int iomap_writepage(struct page *page, struct writeback_control *wbc,
> +		struct iomap_writepage_ctx *wpc,
> +		const struct iomap_writeback_ops *ops);
> +int iomap_writepages(struct address_space *mapping,
> +		struct writeback_control *wbc, struct iomap_writepage_ctx *wpc,
> +		const struct iomap_writeback_ops *ops);
> +
>  /*
>   * Flags for direct I/O ->end_io:
>   */
> -- 
> 2.20.1
>