Re: [PATCH v2 05/10] udp_vu: Pass iov explicitly to helpers instead of using file-scoped array

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

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On Fri, Apr 03, 2026 at 06:38:06PM +0200, Laurent Vivier wrote:
> udp_vu_sock_recv(), udp_vu_prepare(), and udp_vu_csum() all operated on
> the file-scoped iov_vu[] array directly.  Pass iov and count as explicit
> parameters instead, and move iov_vu[] and elem[] to function-local
> statics in udp_vu_sock_to_tap(), the only function that needs them.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>

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

One cosmetic nit noted.

> ---
>  udp_vu.c | 64 +++++++++++++++++++++++++++++---------------------------
>  1 file changed, 33 insertions(+), 31 deletions(-)
> 
> diff --git a/udp_vu.c b/udp_vu.c
> index 34f39e1256f8..9688fe1fdc5c 100644
> --- a/udp_vu.c
> +++ b/udp_vu.c
> @@ -33,9 +33,6 @@
>  #include "udp_vu.h"
>  #include "vu_common.h"
>  
> -static struct iovec     iov_vu		[VIRTQUEUE_MAX_SIZE];
> -static struct vu_virtq_element	elem		[VIRTQUEUE_MAX_SIZE];
> -
>  /**
>   * udp_vu_hdrlen() - Sum size of all headers, from UDP to virtio-net
>   * @v6:		Set for IPv6 packet
> @@ -58,14 +55,14 @@ static size_t udp_vu_hdrlen(bool v6)
>  
>  /**
>   * udp_vu_sock_recv() - Receive datagrams from socket into vhost-user buffers
> + * @iov:	IO vector for the frame (in/out)
> + * @cnt:	Number of IO vector entries (in/out)

Nit: this new description loses some details about the value of *@cnt
on output.

>   * @s:		Socket to receive from
>   * @v6:		Set for IPv6 connections
> - * @iov_cnt:	Number of collected iov in iov_vu (input)
> - * 		Number of iov entries used to store the datagram (output)
>   *
>   * Return: size of received data, -1 on error
>   */
> -static ssize_t udp_vu_sock_recv(int s, bool v6, size_t *iov_cnt)
> +static ssize_t udp_vu_sock_recv(struct iovec *iov, size_t *cnt, int s, bool v6)
>  {
>  	struct msghdr msg  = { 0 };
>  	size_t hdrlen, l2len;
> @@ -75,27 +72,27 @@ static ssize_t udp_vu_sock_recv(int s, bool v6, size_t *iov_cnt)
>  	hdrlen = udp_vu_hdrlen(v6);
>  
>  	/* reserve space for the headers */
> -	assert(iov_vu[0].iov_len >= MAX(hdrlen, ETH_ZLEN + VNET_HLEN));
> -	iov_vu[0].iov_base = (char *)iov_vu[0].iov_base + hdrlen;
> -	iov_vu[0].iov_len -= hdrlen;
> +	assert(iov[0].iov_len >= MAX(hdrlen, ETH_ZLEN + VNET_HLEN));
> +	iov[0].iov_base = (char *)iov[0].iov_base + hdrlen;
> +	iov[0].iov_len -= hdrlen;
>  
>  	/* read data from the socket */
> -	msg.msg_iov = iov_vu;
> -	msg.msg_iovlen = *iov_cnt;
> +	msg.msg_iov = iov;
> +	msg.msg_iovlen = *cnt;
>  
>  	dlen = recvmsg(s, &msg, 0);
>  	if (dlen < 0)
>  		return -1;
>  
>  	/* restore the pointer to the headers address */
> -	iov_vu[0].iov_base = (char *)iov_vu[0].iov_base - hdrlen;
> -	iov_vu[0].iov_len += hdrlen;
> +	iov[0].iov_base = (char *)iov[0].iov_base - hdrlen;
> +	iov[0].iov_len += hdrlen;
>  
> -	*iov_cnt = iov_truncate(iov_vu, *iov_cnt, dlen + hdrlen);
> +	*cnt = iov_truncate(iov, *cnt, dlen + hdrlen);
>  
>  	/* pad frame to 60 bytes: first buffer is at least ETH_ZLEN long */
>  	l2len = dlen + hdrlen - VNET_HLEN;
> -	vu_pad(&iov_vu[0], l2len);
> +	vu_pad(&iov[0], l2len);
>  
>  	return dlen;
>  }
> @@ -103,27 +100,28 @@ static ssize_t udp_vu_sock_recv(int s, bool v6, size_t *iov_cnt)
>  /**
>   * udp_vu_prepare() - Prepare the packet header
>   * @c:		Execution context
> + * @iov:	IO vector for the frame (including vnet header)
>   * @toside:	Address information for one side of the flow
>   * @dlen:	Packet data length
>   *
>   * Return: Layer-4 length
>   */
> -static size_t udp_vu_prepare(const struct ctx *c,
> +static size_t udp_vu_prepare(const struct ctx *c, const struct iovec *iov,
>  			     const struct flowside *toside, ssize_t dlen)
>  {
>  	struct ethhdr *eh;
>  	size_t l4len;
>  
>  	/* ethernet header */
> -	eh = vu_eth(iov_vu[0].iov_base);
> +	eh = vu_eth(iov[0].iov_base);
>  
>  	memcpy(eh->h_dest, c->guest_mac, sizeof(eh->h_dest));
>  	memcpy(eh->h_source, c->our_tap_mac, sizeof(eh->h_source));
>  
>  	/* initialize header */
>  	if (inany_v4(&toside->eaddr) && inany_v4(&toside->oaddr)) {
> -		struct iphdr *iph = vu_ip(iov_vu[0].iov_base);
> -		struct udp_payload_t *bp = vu_payloadv4(iov_vu[0].iov_base);
> +		struct iphdr *iph = vu_ip(iov[0].iov_base);
> +		struct udp_payload_t *bp = vu_payloadv4(iov[0].iov_base);
>  
>  		eh->h_proto = htons(ETH_P_IP);
>  
> @@ -131,8 +129,8 @@ static size_t udp_vu_prepare(const struct ctx *c,
>  
>  		l4len = udp_update_hdr4(iph, bp, toside, dlen, true);
>  	} else {
> -		struct ipv6hdr *ip6h = vu_ip(iov_vu[0].iov_base);
> -		struct udp_payload_t *bp = vu_payloadv6(iov_vu[0].iov_base);
> +		struct ipv6hdr *ip6h = vu_ip(iov[0].iov_base);
> +		struct udp_payload_t *bp = vu_payloadv6(iov[0].iov_base);
>  
>  		eh->h_proto = htons(ETH_P_IPV6);
>  
> @@ -147,23 +145,25 @@ static size_t udp_vu_prepare(const struct ctx *c,
>  /**
>   * udp_vu_csum() - Calculate and set checksum for a UDP packet
>   * @toside:	Address information for one side of the flow
> - * @iov_used:	Number of used iov_vu items
> + * @iov:	IO vector for the frame
> + * @cnt:	Number of IO vector entries
>   */
> -static void udp_vu_csum(const struct flowside *toside, int iov_used)
> +static void udp_vu_csum(const struct flowside *toside, const struct iovec *iov,
> +			size_t cnt)
>  {
>  	const struct in_addr *src4 = inany_v4(&toside->oaddr);
>  	const struct in_addr *dst4 = inany_v4(&toside->eaddr);
> -	char *base = iov_vu[0].iov_base;
> +	char *base = iov[0].iov_base;
>  	struct udp_payload_t *bp;
>  	struct iov_tail data;
>  
>  	if (src4 && dst4) {
>  		bp = vu_payloadv4(base);
> -		data = IOV_TAIL(iov_vu, iov_used, (char *)&bp->data - base);
> +		data = IOV_TAIL(iov, cnt, (char *)&bp->data - base);
>  		csum_udp4(&bp->uh, *src4, *dst4, &data);
>  	} else {
>  		bp = vu_payloadv6(base);
> -		data = IOV_TAIL(iov_vu, iov_used, (char *)&bp->data - base);
> +		data = IOV_TAIL(iov, cnt, (char *)&bp->data - base);
>  		csum_udp6(&bp->uh, &toside->oaddr.a6, &toside->eaddr.a6, &data);
>  	}
>  }
> @@ -178,7 +178,9 @@ static void udp_vu_csum(const struct flowside *toside, int iov_used)
>  void udp_vu_sock_to_tap(const struct ctx *c, int s, int n, flow_sidx_t tosidx)
>  {
>  	const struct flowside *toside = flowside_at_sidx(tosidx);
> +	static struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE];
>  	bool v6 = !(inany_v4(&toside->eaddr) && inany_v4(&toside->oaddr));
> +	static struct iovec iov_vu[VIRTQUEUE_MAX_SIZE];
>  	struct vu_dev *vdev = c->vdev;
>  	struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
>  	int i;
> @@ -211,9 +213,9 @@ void udp_vu_sock_to_tap(const struct ctx *c, int s, int n, flow_sidx_t tosidx)
>  
>  		assert((size_t)elem_cnt == iov_cnt);	/* one iovec per element */
>  
> -		dlen = udp_vu_sock_recv(s, v6, &iov_cnt);
> +		dlen = udp_vu_sock_recv(iov_vu, &iov_cnt, s, v6);
>  		if (dlen < 0) {
> -			vu_queue_rewind(vq, iov_cnt);
> +			vu_queue_rewind(vq, elem_cnt);
>  			break;
>  		}
>  
> @@ -223,12 +225,12 @@ void udp_vu_sock_to_tap(const struct ctx *c, int s, int n, flow_sidx_t tosidx)
>  		vu_queue_rewind(vq, elem_cnt - elem_used);
>  
>  		if (iov_cnt > 0) {
> -			udp_vu_prepare(c, toside, dlen);
> +			udp_vu_prepare(c, iov_vu, toside, dlen);
>  			if (*c->pcap) {
> -				udp_vu_csum(toside, iov_cnt);
> +				udp_vu_csum(toside, iov_vu, iov_cnt);
>  				pcap_iov(iov_vu, iov_cnt, VNET_HLEN);
>  			}
<> -			vu_flush(vdev, vq, elem, iov_cnt);
> +			vu_flush(vdev, vq, elem, elem_used);
>  			vu_queue_notify(vdev, vq);
>  		}
>  	}
> -- 
> 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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