Re: [PATCH 02/25] iomap: add support for data checksumming

["Pankaj Raghav (Samsung)" <pankaj.raghav@linux.dev>]

On Wed, Nov 04, 2026 at 09:57:06AM +0100, Christoph Hellwig wrote:
> Add a new refcounted structure for a data checksum attached to

I don't see any new refcounted structure. Probably the commit message is
stale?

> an iomap_ioend, and helpers to allocate, split and access it.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
>  
>  /*
>   * Flags that if set on either ioend prevent the merge of two ioends.
> @@ -522,14 +529,31 @@ static inline u16 iomap_ioend_flags(const struct iomap *iomap)
>  struct iomap_ioend {
>  	struct list_head	io_list;	/* next ioend in chain */
>  	u16			io_flags;	/* IOMAP_IOEND_* */
> +	u8			io_csum_shift;	/* ilog(2) of csum size */
>  	u32			io_bvec_offset;	/* offset into first bvec */
>  	struct inode		*io_inode;	/* file being written to */
>  	size_t			io_size;	/* size of the extent */
>  	atomic_t		io_remaining;	/* completetion defer count */
>  	int			io_error;	/* stashed away status */
> -	struct iomap_ioend	*io_parent;	/* parent for completions */
> +
> +	/*
> +	 * There are two kinds of ioend, the original ones submitted by iomap,
> +	 * and thus split of for I/O size limitations.  For the latter,

s/thus split of/those split off

> +	 * io_parent points to the original ioend.  For the original ioends,
> +	 * the space used by the parent pointer is reused by the checksum
> +	 * pointer when data checksum are used.  Split ioends always point
> +	 * into the original allocation with their io_csum pointer.  As a
> +	 * special case tiny checksum use the pointer as actual checksum
> +	 * storage if that fits.
> +	 */
> +	union {
> +		struct iomap_ioend *io_parent;	/* parent for completions */
> +		void		*io_csum_alloc; /* original csum allocation. */
> +		u8		io_csum_inline[sizeof(void *)];
> +	};
>  	loff_t			io_offset;	/* offset in the file */
>  	sector_t		io_sector;	/* start sector of ioend */
> +	void			*io_csum;	/* data checksum */
>  	void			*io_private;	/* file system private data */
>  	struct fsverity_info	*io_vi;		/* fsverity info */
>  	struct bio		io_bio;		/* MUST BE LAST! */
> @@ -547,6 +571,22 @@ static inline struct iomap_ioend *iomap_ioend_from_bio(struct bio *bio)
>  	.bi_offset	= (_ioend)->io_bvec_offset,	\
>  }
>  

-- 
Pankaj