Re: [PATCH 2/3] iomap: comment on atomic write checks in iomap_dio_bio_iter()

[Ritesh Harjani (IBM) <ritesh.list@gmail.com>]

John Garry <john.g.garry@oracle.com> writes:

> Help explain the code.
>
> Also clarify the comment for bio size check.

Looks good to me. Feel free to add:

Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>



>
> Signed-off-by: John Garry <john.g.garry@oracle.com>
> ---
>  fs/iomap/direct-io.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 8c1bec473586..b9f59ca43c15 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -350,6 +350,11 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
>  		bio_opf |= REQ_OP_WRITE;
>  
>  		if (iter->flags & IOMAP_ATOMIC_HW) {
> +			/*
> +			 * Ensure that the mapping covers the full write
> +			 * length, otherwise it won't be submitted as a single
> +			 * bio, which is required to use hardware atomics.
> +			 */
>  			if (length != iter->len)
>  				return -EINVAL;
>  			bio_opf |= REQ_ATOMIC;
> @@ -449,7 +454,7 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
>  		n = bio->bi_iter.bi_size;
>  		if (WARN_ON_ONCE((bio_opf & REQ_ATOMIC) && n != length)) {
>  			/*
> -			 * This bio should have covered the complete length,
> +			 * An atomic write bio must cover the complete length,
>  			 * which it doesn't, so error. We may need to zero out
>  			 * the tail (complete FS block), similar to when
>  			 * bio_iov_iter_get_pages() returns an error, above.
> -- 
> 2.31.1