Re: [PATCH 4/4] io_uring/rsrc: send exact nr_segs for fixed buffer

[Pavel Begunkov <asml.silence@gmail.com>]

On 4/17/25 10:32, Pavel Begunkov wrote:
> From: Nitesh Shetty <nj.shetty@samsung.com>
...
> diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
> index 5cf854318b1d..4099b8225670 100644
> --- a/io_uring/rsrc.c
> +++ b/io_uring/rsrc.c
> @@ -1037,6 +1037,7 @@ static int io_import_fixed(int ddir, struct iov_iter *iter,
>   			   u64 buf_addr, size_t len)
>   {
>   	const struct bio_vec *bvec;
> +	size_t folio_mask;
>   	unsigned nr_segs;
>   	size_t offset;
>   	int ret;
> @@ -1067,6 +1068,7 @@ static int io_import_fixed(int ddir, struct iov_iter *iter,
>   	 * 2) all bvecs are the same in size, except potentially the
>   	 *    first and last bvec
>   	 */
> +	folio_mask = (1UL << imu->folio_shift) - 1;
>   	bvec = imu->bvec;
>   	if (offset >= bvec->bv_len) {
>   		unsigned long seg_skip;
> @@ -1075,10 +1077,10 @@ static int io_import_fixed(int ddir, struct iov_iter *iter,
>   		offset -= bvec->bv_len;
>   		seg_skip = 1 + (offset >> imu->folio_shift);
>   		bvec += seg_skip;
> -		offset &= (1UL << imu->folio_shift) - 1;
> +		offset &= folio_mask;
>   	}
>   
> -	nr_segs = imu->nr_bvecs - (bvec - imu->bvec);
> +	nr_segs = (offset + len + folio_mask) >> imu->folio_shift;

Nitesh, let me know if you're happy with this version.

>   	iov_iter_bvec(iter, ddir, bvec, nr_segs, len);
>   	iter->iov_offset = offset;
>   	return 0;

-- 
Pavel Begunkov