Re: [PATCH 10/12] vu_common: Accept explicit iovec count per element in vu_init_elem()

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Feb 27, 2026 at 03:03:28PM +0100, Laurent Vivier wrote:
> Extend vu_init_elem() to accept an iov_per_elem parameter specifying
> how many iovec entries to assign to each virtqueue element. The iov
> array is now strided by iov_per_elem rather than 1.
> 
> Update all callers to pass 1, preserving existing behavior.
> 
> No functional change.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  tcp_vu.c    |  2 +-
>  udp_vu.c    |  2 +-
>  vu_common.c | 19 ++++++++++---------
>  vu_common.h |  2 +-
>  4 files changed, 13 insertions(+), 12 deletions(-)
> 
> diff --git a/tcp_vu.c b/tcp_vu.c
> index 77d6e75496a0..51f7834f0307 100644
> --- a/tcp_vu.c
> +++ b/tcp_vu.c
> @@ -202,7 +202,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq,
>  
>  	hdrlen = tcp_vu_hdrlen(v6);
>  
> -	vu_init_elem(elem, &iov_vu[DISCARD_IOV_NUM], ARRAY_SIZE(elem));
> +	vu_init_elem(elem, &iov_vu[DISCARD_IOV_NUM], ARRAY_SIZE(elem), 1);
>  
>  	elem_cnt = 0;
>  	*head_cnt = 0;
> diff --git a/udp_vu.c b/udp_vu.c
> index 5ae79b9bb0c5..7e486b74883e 100644
> --- a/udp_vu.c
> +++ b/udp_vu.c
> @@ -214,7 +214,7 @@ void udp_vu_sock_to_tap(const struct ctx *c, int s, int n, flow_sidx_t tosidx)
>  		int elem_cnt, elem_used;
>  		ssize_t dlen;
>  
> -		vu_init_elem(elem, iov_vu, ARRAY_SIZE(elem));
> +		vu_init_elem(elem, iov_vu, ARRAY_SIZE(elem), 1);
>  
>  		elem_cnt = vu_collect(vdev, vq, elem, ARRAY_SIZE(elem),
>  				      IP_MAX_MTU + ETH_HLEN + VNET_HLEN, NULL);
> diff --git a/vu_common.c b/vu_common.c
> index b6753a556049..e32a56d881a3 100644
> --- a/vu_common.c
> +++ b/vu_common.c
> @@ -54,18 +54,19 @@ int vu_packet_check_range(struct vdev_memory *memory,
>  }
>  
>  /**
> - * vu_init_elem() - initialize an array of virtqueue elements with 1 iov in each
> - * @elem:	Array of virtqueue elements to initialize
> - * @iov:	Array of iovec to assign to virtqueue element
> - * @elem_cnt:	Number of virtqueue element
> + * vu_init_elem() - Initialize an array of virtqueue elements
> + * @elem:	  Array of virtqueue elements to initialize
> + * @iov:	  Array of iovecs to assign to virtqueue elements
> + * @elem_cnt:	  Number of virtqueue elements
> + * @iov_per_elem: Number of iovecs per element
>   */
>  void vu_init_elem(struct vu_virtq_element *elem, struct iovec *iov,
> -		  int elem_cnt)
> +		  int elem_cnt, int iov_per_elem)
>  {
> -	int i;
> +	int i, j;
>  
> -	for (i = 0; i < elem_cnt; i++)
> -		vu_set_element(&elem[i], 0, NULL, 1, &iov[i]);
> +	for (i = 0, j = 0; i < elem_cnt; i++, j += iov_per_elem)
> +		vu_set_element(&elem[i], 0, NULL, iov_per_elem, &iov[j]);
>  }
>  
>  /**
> @@ -268,7 +269,7 @@ int vu_send_single(const struct ctx *c, const void *buf, size_t size)
>  		return -1;
>  	}
>  
> -	vu_init_elem(elem, in_sg, ARRAY_SIZE(elem));
> +	vu_init_elem(elem, in_sg, ARRAY_SIZE(elem), 1);
>  
>  	size += VNET_HLEN;
>  	elem_cnt = vu_collect(vdev, vq, elem, ARRAY_SIZE(elem), size, &total);
> diff --git a/vu_common.h b/vu_common.h
> index c1d2ce888f12..51639c04df14 100644
> --- a/vu_common.h
> +++ b/vu_common.h
> @@ -48,7 +48,7 @@ static inline void vu_set_element(struct vu_virtq_element *elem,
>  }
>  
>  void vu_init_elem(struct vu_virtq_element *elem, struct iovec *iov,
> -		  int elem_cnt);
> +		  int elem_cnt, int iov_per_elem);
>  int vu_collect(const struct vu_dev *vdev, struct vu_virtq *vq,
>  	       struct vu_virtq_element *elem, int max_elem, size_t size,
>  	       size_t *collected);
> -- 
> 2.53.0
> 

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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