Re: [PATCH 1/2] udp: Allow checksum to be disabled

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

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On Mon, Sep 16, 2024 at 02:16:00PM +0200, Laurent Vivier wrote:
> We can need not to set the UDP checksum. Add a parameter to
> udp_update_hdr4() and udp_update_hdr6() to disable it.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
>  udp.c | 41 +++++++++++++++++++++++++++++++----------
>  1 file changed, 31 insertions(+), 10 deletions(-)
> 
> diff --git a/udp.c b/udp.c
> index 2ba00c9c20a8..64a0d9f9dba2 100644
> --- a/udp.c
> +++ b/udp.c
> @@ -298,11 +298,13 @@ static void udp_splice_send(const struct ctx *c, size_t start, size_t n,
>   * @bp:		Pointer to udp_payload_t to update
>   * @toside:	Flowside for destination side
>   * @dlen:	Length of UDP payload
> + * @no_udp_csum: Do not set UPD checksum

s/UPD/UDP/g :)

Otherwise LGTM.

>   *
>   * Return: size of IPv4 payload (UDP header + data)
>   */
>  static size_t udp_update_hdr4(struct iphdr *ip4h, struct udp_payload_t *bp,
> -			      const struct flowside *toside, size_t dlen)
> +			      const struct flowside *toside, size_t dlen,
> +			      bool no_udp_csum)
>  {
>  	const struct in_addr *src = inany_v4(&toside->oaddr);
>  	const struct in_addr *dst = inany_v4(&toside->eaddr);
> @@ -319,7 +321,10 @@ static size_t udp_update_hdr4(struct iphdr *ip4h, struct udp_payload_t *bp,
>  	bp->uh.source = htons(toside->oport);
>  	bp->uh.dest = htons(toside->eport);
>  	bp->uh.len = htons(l4len);
> -	csum_udp4(&bp->uh, *src, *dst, bp->data, dlen);
> +	if (no_udp_csum)
> +		bp->uh.check = 0;
> +	else
> +		csum_udp4(&bp->uh, *src, *dst, bp->data, dlen);
>  
>  	return l4len;
>  }
> @@ -330,11 +335,13 @@ static size_t udp_update_hdr4(struct iphdr *ip4h, struct udp_payload_t *bp,
>   * @bp:		Pointer to udp_payload_t to update
>   * @toside:	Flowside for destination side
>   * @dlen:	Length of UDP payload
> + * @no_udp_csum: Do not set UPD checksum
>   *
>   * Return: size of IPv6 payload (UDP header + data)
>   */
>  static size_t udp_update_hdr6(struct ipv6hdr *ip6h, struct udp_payload_t *bp,
> -			      const struct flowside *toside, size_t dlen)
> +			      const struct flowside *toside, size_t dlen,
> +			      bool no_udp_csum)
>  {
>  	uint16_t l4len = dlen + sizeof(bp->uh);
>  
> @@ -348,7 +355,16 @@ static size_t udp_update_hdr6(struct ipv6hdr *ip6h, struct udp_payload_t *bp,
>  	bp->uh.source = htons(toside->oport);
>  	bp->uh.dest = htons(toside->eport);
>  	bp->uh.len = ip6h->payload_len;
> -	csum_udp6(&bp->uh, &toside->oaddr.a6, &toside->eaddr.a6, bp->data, dlen);
> +	if (no_udp_csum) {
> +		/* O is an invalid checksum for UDP IPv6 and dropped by
> +		 * the kernel stack, even if the checksum is disabled by virtio
> +		 * flags. We need to put any non-zero value here.
> +		 */
> +		bp->uh.check = 0xffff;
> +	} else {
> +		csum_udp6(&bp->uh, &toside->oaddr.a6, &toside->eaddr.a6,
> +			  bp->data, dlen);
> +	}
>  
>  	return l4len;
>  }
> @@ -358,9 +374,11 @@ static size_t udp_update_hdr6(struct ipv6hdr *ip6h, struct udp_payload_t *bp,
>   * @mmh:	Receiving mmsghdr array
>   * @idx:	Index of the datagram to prepare
>   * @toside:	Flowside for destination side
> + * @no_udp_csum: Do not set UPD checksum
>   */
> -static void udp_tap_prepare(const struct mmsghdr *mmh, unsigned idx,
> -			    const struct flowside *toside)
> +static void udp_tap_prepare(const struct mmsghdr *mmh,
> +			    unsigned idx, const struct flowside *toside,
> +			    bool no_udp_csum)
>  {
>  	struct iovec (*tap_iov)[UDP_NUM_IOVS] = &udp_l2_iov[idx];
>  	struct udp_payload_t *bp = &udp_payload[idx];
> @@ -368,13 +386,15 @@ static void udp_tap_prepare(const struct mmsghdr *mmh, unsigned idx,
>  	size_t l4len;
>  
>  	if (!inany_v4(&toside->eaddr) || !inany_v4(&toside->oaddr)) {
> -		l4len = udp_update_hdr6(&bm->ip6h, bp, toside, mmh[idx].msg_len);
> +		l4len = udp_update_hdr6(&bm->ip6h, bp, toside,
> +					mmh[idx].msg_len, no_udp_csum);
>  		tap_hdr_update(&bm->taph, l4len + sizeof(bm->ip6h) +
>  			       sizeof(udp6_eth_hdr));
>  		(*tap_iov)[UDP_IOV_ETH] = IOV_OF_LVALUE(udp6_eth_hdr);
>  		(*tap_iov)[UDP_IOV_IP] = IOV_OF_LVALUE(bm->ip6h);
>  	} else {
> -		l4len = udp_update_hdr4(&bm->ip4h, bp, toside, mmh[idx].msg_len);
> +		l4len = udp_update_hdr4(&bm->ip4h, bp, toside,
> +					mmh[idx].msg_len, no_udp_csum);
>  		tap_hdr_update(&bm->taph, l4len + sizeof(bm->ip4h) +
>  			       sizeof(udp4_eth_hdr));
>  		(*tap_iov)[UDP_IOV_ETH] = IOV_OF_LVALUE(udp4_eth_hdr);
> @@ -565,7 +585,8 @@ void udp_listen_sock_handler(const struct ctx *c, union epoll_ref ref,
>  				udp_splice_prepare(udp_mh_recv, i);
>  			} else if (batchpif == PIF_TAP) {
>  				udp_tap_prepare(udp_mh_recv, i,
> -						flowside_at_sidx(batchsidx));
> +						flowside_at_sidx(batchsidx),
> +						false);
>  			}
>  
>  			if (++i >= n)
> @@ -636,7 +657,7 @@ void udp_reply_sock_handler(const struct ctx *c, union epoll_ref ref,
>  		if (pif_is_socket(topif))
>  			udp_splice_prepare(udp_mh_recv, i);
>  		else if (topif == PIF_TAP)
> -			udp_tap_prepare(udp_mh_recv, i, toside);
> +			udp_tap_prepare(udp_mh_recv, i, toside, false);
>  		/* Restore sockaddr length clobbered by recvmsg() */
>  		udp_mh_recv[i].msg_hdr.msg_namelen = sizeof(udp_meta[i].s_in);
>  	}

-- 
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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