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

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

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On Mon, Sep 16, 2024 at 02:16:01PM +0200, Laurent Vivier wrote:
> We can need not to set TCP checksum. Add a parameter to
> tcp_fill_headers4() and tcp_fill_headers6() to disable it.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>

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

> ---
>  tcp.c          | 24 +++++++++++++++++-------
>  tcp_buf.c      |  8 +++++---
>  tcp_internal.h |  3 ++-
>  3 files changed, 24 insertions(+), 11 deletions(-)
> 
> diff --git a/tcp.c b/tcp.c
> index f9fe1b9a1330..a44d7b977214 100644
> --- a/tcp.c
> +++ b/tcp.c
> @@ -903,6 +903,7 @@ static void tcp_fill_header(struct tcphdr *th,
>   * @dlen:	TCP payload length
>   * @check:	Checksum, if already known
>   * @seq:	Sequence number for this segment
> + * @no_tcp_csum: Do not set TCP checksum
>   *
>   * Return: The IPv4 payload length, host order
>   */
> @@ -910,7 +911,7 @@ static size_t tcp_fill_headers4(const struct tcp_tap_conn *conn,
>  				struct tap_hdr *taph,
>  				struct iphdr *iph, struct tcphdr *th,
>  				size_t dlen, const uint16_t *check,
> -				uint32_t seq)
> +				uint32_t seq, bool no_tcp_csum)
>  {
>  	const struct flowside *tapside = TAPFLOW(conn);
>  	const struct in_addr *src4 = inany_v4(&tapside->oaddr);
> @@ -929,7 +930,10 @@ static size_t tcp_fill_headers4(const struct tcp_tap_conn *conn,
>  
>  	tcp_fill_header(th, conn, seq);
>  
> -	tcp_update_check_tcp4(iph, th);
> +	if (no_tcp_csum)
> +		th->check = 0;
> +	else
> +		tcp_update_check_tcp4(iph, th);
>  
>  	tap_hdr_update(taph, l3len + sizeof(struct ethhdr));
>  
> @@ -945,13 +949,14 @@ static size_t tcp_fill_headers4(const struct tcp_tap_conn *conn,
>   * @dlen:	TCP payload length
>   * @check:	Checksum, if already known
>   * @seq:	Sequence number for this segment
> + * @no_tcp_csum: Do not set TCP checksum
>   *
>   * Return: The IPv6 payload length, host order
>   */
>  static size_t tcp_fill_headers6(const struct tcp_tap_conn *conn,
>  				struct tap_hdr *taph,
>  				struct ipv6hdr *ip6h, struct tcphdr *th,
> -				size_t dlen, uint32_t seq)
> +				size_t dlen, uint32_t seq, bool no_tcp_csum)
>  {
>  	const struct flowside *tapside = TAPFLOW(conn);
>  	size_t l4len = dlen + sizeof(*th);
> @@ -970,7 +975,10 @@ static size_t tcp_fill_headers6(const struct tcp_tap_conn *conn,
>  
>  	tcp_fill_header(th, conn, seq);
>  
> -	tcp_update_check_tcp6(ip6h, th);
> +	if (no_tcp_csum)
> +		th->check = 0;
> +	else
> +		tcp_update_check_tcp6(ip6h, th);
>  
>  	tap_hdr_update(taph, l4len + sizeof(*ip6h) + sizeof(struct ethhdr));
>  
> @@ -984,12 +992,14 @@ static size_t tcp_fill_headers6(const struct tcp_tap_conn *conn,
>   * @dlen:	TCP payload length
>   * @check:	Checksum, if already known
>   * @seq:	Sequence number for this segment
> + * @no_tcp_csum: Do not set TCP checksum
>   *
>   * Return: IP payload length, host order
>   */
>  size_t tcp_l2_buf_fill_headers(const struct tcp_tap_conn *conn,
>  			       struct iovec *iov, size_t dlen,
> -			       const uint16_t *check, uint32_t seq)
> +			       const uint16_t *check, uint32_t seq,
> +			       bool no_tcp_csum)
>  {
>  	const struct flowside *tapside = TAPFLOW(conn);
>  	const struct in_addr *a4 = inany_v4(&tapside->oaddr);
> @@ -998,13 +1008,13 @@ size_t tcp_l2_buf_fill_headers(const struct tcp_tap_conn *conn,
>  		return tcp_fill_headers4(conn, iov[TCP_IOV_TAP].iov_base,
>  					 iov[TCP_IOV_IP].iov_base,
>  					 iov[TCP_IOV_PAYLOAD].iov_base, dlen,
> -					 check, seq);
> +					 check, seq, no_tcp_csum);
>  	}
>  
>  	return tcp_fill_headers6(conn, iov[TCP_IOV_TAP].iov_base,
>  				 iov[TCP_IOV_IP].iov_base,
>  				 iov[TCP_IOV_PAYLOAD].iov_base, dlen,
> -				 seq);
> +				 seq, no_tcp_csum);
>  }
>  
>  /**
> diff --git a/tcp_buf.c b/tcp_buf.c
> index 1a398461a34b..10a663bdfc26 100644
> --- a/tcp_buf.c
> +++ b/tcp_buf.c
> @@ -320,7 +320,7 @@ int tcp_buf_send_flag(struct ctx *c, struct tcp_tap_conn *conn, int flags)
>  		return ret;
>  	}
>  
> -	l4len = tcp_l2_buf_fill_headers(conn, iov, optlen, NULL, seq);
> +	l4len = tcp_l2_buf_fill_headers(conn, iov, optlen, NULL, seq, false);
>  	iov[TCP_IOV_PAYLOAD].iov_len = l4len;
>  
>  	if (flags & DUP_ACK) {
> @@ -381,7 +381,8 @@ static void tcp_data_to_tap(struct ctx *c, struct tcp_tap_conn *conn,
>  		tcp4_frame_conns[tcp4_payload_used] = conn;
>  
>  		iov = tcp4_l2_iov[tcp4_payload_used++];
> -		l4len = tcp_l2_buf_fill_headers(conn, iov, dlen, check, seq);
> +		l4len = tcp_l2_buf_fill_headers(conn, iov, dlen, check, seq,
> +						false);
>  		iov[TCP_IOV_PAYLOAD].iov_len = l4len;
>  		if (tcp4_payload_used > TCP_FRAMES_MEM - 1)
>  			tcp_payload_flush(c);
> @@ -389,7 +390,8 @@ static void tcp_data_to_tap(struct ctx *c, struct tcp_tap_conn *conn,
>  		tcp6_frame_conns[tcp6_payload_used] = conn;
>  
>  		iov = tcp6_l2_iov[tcp6_payload_used++];
> -		l4len = tcp_l2_buf_fill_headers(conn, iov, dlen, NULL, seq);
> +		l4len = tcp_l2_buf_fill_headers(conn, iov, dlen, NULL, seq,
> +						false);
>  		iov[TCP_IOV_PAYLOAD].iov_len = l4len;
>  		if (tcp6_payload_used > TCP_FRAMES_MEM - 1)
>  			tcp_payload_flush(c);
> diff --git a/tcp_internal.h b/tcp_internal.h
> index aa8bb64f1f33..e7fe735bfcb4 100644
> --- a/tcp_internal.h
> +++ b/tcp_internal.h
> @@ -91,7 +91,8 @@ void tcp_rst_do(struct ctx *c, struct tcp_tap_conn *conn);
>  
>  size_t tcp_l2_buf_fill_headers(const struct tcp_tap_conn *conn,
>  			       struct iovec *iov, size_t dlen,
> -			       const uint16_t *check, uint32_t seq);
> +			       const uint16_t *check, uint32_t seq,
> +			       bool no_tcp_csum);
>  int tcp_update_seqack_wnd(const struct ctx *c, struct tcp_tap_conn *conn,
>  			  int force_seq, struct tcp_info *tinfo);
>  int tcp_prepare_flags(struct ctx *c, struct tcp_tap_conn *conn, int flags,

-- 
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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