Re: [PATCH v2 10/12] iomap: remove unnecessary advance from iomap_iter()

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Feb 19, 2025 at 12:50:48PM -0500, Brian Foster wrote:
> At this point, all iomap operations have been updated to advance the
> iomap_iter directly before returning to iomap_iter(). Therefore, the
> complexity of handling both the old and new semantics is no longer
> required and can be removed from iomap_iter().
> 
> Update iomap_iter() to expect success or failure status in
> iter.processed. As a precaution and developer hint to prevent
> inadvertent use of old semantics, warn on a positive return code and
> fail the operation. Remove the unnecessary advance and simplify the
> termination logic.
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>

Looks reasonable,
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  fs/iomap/iter.c | 39 +++++++++++++++------------------------
>  1 file changed, 15 insertions(+), 24 deletions(-)
> 
> diff --git a/fs/iomap/iter.c b/fs/iomap/iter.c
> index 0ebcabc7df52..e4dfe64029cc 100644
> --- a/fs/iomap/iter.c
> +++ b/fs/iomap/iter.c
> @@ -60,9 +60,8 @@ static inline void iomap_iter_done(struct iomap_iter *iter)
>  int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops)
>  {
>  	bool stale = iter->iomap.flags & IOMAP_F_STALE;
> -	ssize_t advanced = iter->processed > 0 ? iter->processed : 0;
> -	u64 olen = iter->len;
> -	s64 processed;
> +	ssize_t advanced;
> +	u64 olen;
>  	int ret;
>  
>  	trace_iomap_iter(iter, ops, _RET_IP_);
> @@ -71,14 +70,11 @@ int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops)
>  		goto begin;
>  
>  	/*
> -	 * If iter.processed is zero, the op may still have advanced the iter
> -	 * itself. Calculate the advanced and original length bytes based on how
> -	 * far pos has advanced for ->iomap_end().
> +	 * Calculate how far the iter was advanced and the original length bytes
> +	 * for ->iomap_end().
>  	 */
> -	if (!advanced) {
> -		advanced = iter->pos - iter->iter_start_pos;
> -		olen += advanced;
> -	}
> +	advanced = iter->pos - iter->iter_start_pos;
> +	olen = iter->len + advanced;
>  
>  	if (ops->iomap_end) {
>  		ret = ops->iomap_end(iter->inode, iter->iter_start_pos,
> @@ -89,27 +85,22 @@ int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops)
>  			return ret;
>  	}
>  
> -	processed = iter->processed;
> -	if (processed < 0) {
> -		iomap_iter_reset_iomap(iter);
> -		return processed;
> -	}
> +	/* detect old return semantics where this would advance */
> +	if (WARN_ON_ONCE(iter->processed > 0))
> +		iter->processed = -EIO;
>  
>  	/*
> -	 * Advance the iter and clear state from the previous iteration. This
> -	 * passes iter->processed because that reflects the bytes processed but
> -	 * not yet advanced by the iter handler.
> -	 *
>  	 * Use iter->len to determine whether to continue onto the next mapping.
> -	 * Explicitly terminate in the case where the current iter has not
> +	 * Explicitly terminate on error status or if the current iter has not
>  	 * advanced at all (i.e. no work was done for some reason) unless the
>  	 * mapping has been marked stale and needs to be reprocessed.
>  	 */
> -	ret = iomap_iter_advance(iter, &processed);
> -	if (!ret && iter->len > 0)
> -		ret = 1;
> -	if (ret > 0 && !advanced && !stale)
> +	if (iter->processed < 0)
> +		ret = iter->processed;
> +	else if (iter->len == 0 || (!advanced && !stale))
>  		ret = 0;
> +	else
> +		ret = 1;
>  	iomap_iter_reset_iomap(iter);
>  	if (ret <= 0)
>  		return ret;
> -- 
> 2.48.1
> 
>