Re: [PATCH v2 12/20] tcp: Convert tcp_data_from_tap() to use iov_tail

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

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On Fri, Apr 11, 2025 at 03:10:22PM +0200, Laurent Vivier wrote:
> Use packet_base() and extract headers using IOV_PEEK_HEADER()
> rather than packet_get().
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
>  tcp.c | 30 +++++++++++++++++++-----------
>  1 file changed, 19 insertions(+), 11 deletions(-)
> 
> diff --git a/tcp.c b/tcp.c
> index 1838b73cf766..bebbb01b39f5 100644
> --- a/tcp.c
> +++ b/tcp.c
> @@ -1651,15 +1651,21 @@ static int tcp_data_from_tap(const struct ctx *c, struct tcp_tap_conn *conn,
>  	for (i = idx, iov_i = 0; i < (int)p->count; i++) {
>  		uint32_t seq, seq_offset, ack_seq;
>  		const struct tcphdr *th;
> -		char *data;
> -		size_t off;
> +		struct iov_tail data;
> +		struct tcphdr thc;
> +		size_t off, size;
> +		int count;
>  
> -		th = packet_get(p, i, 0, sizeof(*th), &len);
> +		if (!packet_base(p, i, &data))
> +			return -1;
> +
> +		th = IOV_PEEK_HEADER(&data, thc);
>  		if (!th)
>  			return -1;
> -		len += sizeof(*th);
> +		len = iov_tail_size(&data);
>  
>  		off = th->doff * 4UL;
> +
>  		if (off < sizeof(*th) || off > len)
>  			return -1;
>  
> @@ -1669,9 +1675,7 @@ static int tcp_data_from_tap(const struct ctx *c, struct tcp_tap_conn *conn,
>  		}
>  
>  		len -= off;
> -		data = packet_get(p, i, off, len, NULL);
> -		if (!data)
> -			continue;
> +		iov_tail_drop(&data, off);
>  
>  		seq = ntohl(th->seq);
>  		if (SEQ_LT(seq, conn->seq_from_tap) && len <= 1) {
> @@ -1745,10 +1749,14 @@ static int tcp_data_from_tap(const struct ctx *c, struct tcp_tap_conn *conn,
>  			continue;
>  		}
>  
> -		tcp_iov[iov_i].iov_base = data + seq_offset;
> -		tcp_iov[iov_i].iov_len = len - seq_offset;
> -		seq_from_tap += tcp_iov[iov_i].iov_len;
> -		iov_i++;
> +		size = len - seq_offset;
> +		count = iov_slice(&tcp_iov[iov_i], UIO_MAXIOV - iov_i,
> +				  &data.iov[0], data.cnt, data.off + seq_offset,
> +				  &size);

Here's another use case for that iov_slice() wrapper

> +		if (count < 0)
> +			break;
> +		seq_from_tap += size;
> +		iov_i += count;
>  
>  		if (keep == i)
>  			keep = -1;

-- 
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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