linux-kernel - Re: [PATCH v6 02/13] iomap: comment on atomic write checks in iomap_dio_bio

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Message-ID: <87senbspx3.fsf@gmail.com>
Date: Mon, 17 Mar 2025 19:46:40 +0530
From: Ritesh Harjani (IBM) <ritesh.list@...il.com>
To: John Garry <john.g.garry@...cle.com>, brauner@...nel.org, djwong@...nel.org, cem@...nel.org, dchinner@...hat.com, hch@....de
Cc: linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, ojaswin@...ux.ibm.com, martin.petersen@...cle.com, tytso@....edu, linux-ext4@...r.kernel.org, John Garry <john.g.garry@...cle.com>
Subject: Re: [PATCH v6 02/13] iomap: comment on atomic write checks in iomap_dio_bio_iter()

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

> Help explain the code.
>
> Also clarify the comment for bio size check.
>
> Signed-off-by: John Garry <john.g.garry@...cle.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..9d72b99cb447 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 we will submit multiple BIOs, which is
> +			* disallowed.
> +			*/

Nit: IMO, this can be clubbed together with your next patch PATCH-03 itself.
But either ways, no strong preference.

-ritesh

>  			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