Re: [PATCH 10/18] tcp: Convert tcp_tap_handler() to use iov_tail

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

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On Wed, Apr 02, 2025 at 07:23:35PM +0200, Laurent Vivier wrote:
> Use packet_base() and extract headers using IOV_REMOVE_HEADER()
> and iov_peek_header_() rather than packet_get().
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
>  tcp.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/tcp.c b/tcp.c
> index a4c840e6721c..790714a08793 100644
> --- a/tcp.c
> +++ b/tcp.c
> @@ -310,6 +310,8 @@
>  #include "tcp_buf.h"
>  #include "tcp_vu.h"
>  

Some explanation of the derivation would be good here.

> +#define OPTLEN_MAX (((1UL << 4) - 6) * 4UL)
> +
>  #ifndef __USE_MISC
>  /* From Linux UAPI, missing in netinet/tcp.h provided by musl */
>  struct tcp_repair_opt {
> @@ -1957,7 +1959,10 @@ int tcp_tap_handler(const struct ctx *c, uint8_t pif, sa_family_t af,
>  {
>  	struct tcp_tap_conn *conn;
>  	const struct tcphdr *th;
> +	char optsc[OPTLEN_MAX];
> +	struct iov_tail data;
>  	size_t optlen, len;
> +	struct tcphdr thc;
>  	const char *opts;
>  	union flow *flow;
>  	flow_sidx_t sidx;
> @@ -1966,15 +1971,19 @@ int tcp_tap_handler(const struct ctx *c, uint8_t pif, sa_family_t af,
>  
>  	(void)pif;
>  
> -	th = packet_get(p, idx, 0, sizeof(*th), &len);
> +	if (!packet_base(p, idx, &data))
> +		return 1;
> +
> +	len = iov_tail_size(&data);

'l4len', please.

> +
> +	th = IOV_REMOVE_HEADER(&data, thc);
>  	if (!th)
>  		return 1;
> -	len += sizeof(*th);
>  
>  	optlen = th->doff * 4UL - sizeof(*th);
>  	/* Static checkers might fail to see this: */
> -	optlen = MIN(optlen, ((1UL << 4) /* from doff width */ - 6) * 4UL);
> -	opts = packet_get(p, idx, sizeof(*th), optlen, NULL);
> +	optlen = MIN(optlen, OPTLEN_MAX);
> +	opts = (char *)iov_peek_header_(&data, &optsc[0], optlen, 1);
>  
>  	sidx = flow_lookup_af(c, IPPROTO_TCP, PIF_TAP, af, saddr, daddr,
>  			      ntohs(th->source), ntohs(th->dest));

-- 
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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