Re: [PATCH v4 05/23] ext4: implement buffered read path using iomap

[Ojaswin Mujoo]

On Mon, May 11, 2026 at 03:23:25PM +0800, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@xxxxxxxxxx>
> 
> Implement the iomap read path for ext4 by introducing a new
> ext4_iomap_buffered_read_ops instance. This provides the read_folio()
> and readahead() callbacks for ext4_iomap_aops. The implementation
> introduces:
> 
>  - ext4_iomap_map_blocks(): Helper function to query extent mappings for
>    a given read range using ext4_map_blocks() and convert the mapping
>    information to iomap type
>  - ext4_iomap_buffered_read_begin(): The iomap_begin callback that maps
>    blocks, validates filesystem state, and populates the iomap. It
>    returns -ERANGE for inline data which is not yet supported.
> 
> Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
> Reviewed-by: Jan Kara <jack@xxxxxxx>

Looks good, feel free to add:

Reviewed-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>

Regards,
Ojaswin

> ---
>  fs/ext4/inode.c | 45 ++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 44 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 178ac2be37b7..6c4d9137b279 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3908,14 +3908,57 @@ const struct iomap_ops ext4_iomap_report_ops = {
>  	.iomap_begin = ext4_iomap_begin_report,
>  };
>  
> +static int ext4_iomap_map_blocks(struct inode *inode, loff_t offset,
> +		loff_t length, struct ext4_map_blocks *map)
> +{
> +	u8 blkbits = inode->i_blkbits;
> +
> +	if ((offset >> blkbits) > EXT4_MAX_LOGICAL_BLOCK)
> +		return -EINVAL;
> +
> +	/* Calculate the first and last logical blocks respectively. */
> +	map->m_lblk = offset >> blkbits;
> +	map->m_len = min_t(loff_t, (offset + length - 1) >> blkbits,
> +			   EXT4_MAX_LOGICAL_BLOCK) - map->m_lblk + 1;
> +
> +	return ext4_map_blocks(NULL, inode, map, 0);
> +}
> +
> +static int ext4_iomap_buffered_read_begin(struct inode *inode, loff_t offset,
> +		loff_t length, unsigned int flags, struct iomap *iomap,
> +		struct iomap *srcmap)
> +{
> +	struct ext4_map_blocks map;
> +	int ret;
> +
> +	if (unlikely(ext4_forced_shutdown(inode->i_sb)))
> +		return -EIO;
> +
> +	/* Inline data support is not yet available. */
> +	if (WARN_ON_ONCE(ext4_has_inline_data(inode)))
> +		return -ERANGE;
> +
> +	ret = ext4_iomap_map_blocks(inode, offset, length, &map);
> +	if (ret < 0)
> +		return ret;
> +
> +	ext4_set_iomap(inode, iomap, &map, offset, length, flags);
> +	return 0;
> +}
> +
> +const struct iomap_ops ext4_iomap_buffered_read_ops = {
> +	.iomap_begin = ext4_iomap_buffered_read_begin,
> +};
> +
>  static int ext4_iomap_read_folio(struct file *file, struct folio *folio)
>  {
> +	iomap_bio_read_folio(folio, &ext4_iomap_buffered_read_ops);
>  	return 0;
>  }
>  
>  static void ext4_iomap_readahead(struct readahead_control *rac)
>  {
> -
> +	iomap_bio_readahead(rac, &ext4_iomap_buffered_read_ops);
>  }
>  
>  static int ext4_iomap_writepages(struct address_space *mapping,
> -- 
> 2.52.0
>