Re: [PATCH v8 19/30] tap: Convert tap4_handler() to iov_tail

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

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On Tue, Aug 05, 2025 at 05:46:17PM +0200, Laurent Vivier wrote:
> Use packet_data() and extract headers using IOV_PEEK_HEADER()
> rather than packet_get().
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>

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

> ---
>  tap.c | 33 ++++++++++++++++++++-------------
>  1 file changed, 20 insertions(+), 13 deletions(-)
> 
> diff --git a/tap.c b/tap.c
> index d7852fad6069..4fbcad3b385f 100644
> --- a/tap.c
> +++ b/tap.c
> @@ -706,28 +706,34 @@ static int tap4_handler(struct ctx *c, const struct pool *in,
>  	i = 0;
>  resume:
>  	for (seq_count = 0, seq = NULL; i < in->count; i++) {
> -		size_t l2len, l3len, hlen, l4len;
> +		size_t l3len, hlen, l4len;
> +		struct ethhdr eh_storage;
> +		struct iphdr iph_storage;
> +		struct udphdr uh_storage;
>  		const struct ethhdr *eh;
>  		const struct udphdr *uh;
>  		struct iov_tail data;
>  		struct iphdr *iph;
> -		const char *l4h;
>  
> -		packet_get(in, i, 0, 0, &l2len);
> +		if (!packet_data(in, i, &data))
> +			continue;
>  
> -		eh = packet_get(in, i, 0, sizeof(*eh), &l3len);
> +		eh = IOV_PEEK_HEADER(&data, eh_storage);
>  		if (!eh)
>  			continue;
>  		if (ntohs(eh->h_proto) == ETH_P_ARP) {
>  			PACKET_POOL_P(pkt, 1, in->buf, in->buf_size);
>  
> -			data = IOV_TAIL_FROM_BUF((void *)eh, l2len, 0);
>  			packet_add(pkt, &data);
>  			arp(c, pkt);
>  			continue;
>  		}
>  
> -		iph = packet_get(in, i, sizeof(*eh), sizeof(*iph), NULL);
> +		if (!iov_tail_drop(&data, sizeof(*eh)))
> +			continue;
> +		l3len = iov_tail_size(&data);
> +
> +		iph = IOV_PEEK_HEADER(&data, iph_storage);
>  		if (!iph)
>  			continue;
>  
> @@ -755,8 +761,9 @@ resume:
>  		if (iph->saddr && c->ip4.addr_seen.s_addr != iph->saddr)
>  			c->ip4.addr_seen.s_addr = iph->saddr;
>  
> -		l4h = packet_get(in, i, sizeof(*eh) + hlen, l4len, NULL);
> -		if (!l4h)
> +		if (!iov_tail_drop(&data, hlen))
> +			continue;
> +		if (iov_tail_size(&data) != l4len)
>  			continue;
>  
>  		if (iph->protocol == IPPROTO_ICMP) {
> @@ -767,7 +774,6 @@ resume:
>  
>  			tap_packet_debug(iph, NULL, NULL, 0, NULL, 1);
>  
> -			data = IOV_TAIL_FROM_BUF((void *)l4h, l4len, 0);
>  			packet_add(pkt, &data);
>  			icmp_tap_handler(c, PIF_TAP, AF_INET,
>  					 &iph->saddr, &iph->daddr,
> @@ -775,15 +781,17 @@ resume:
>  			continue;
>  		}
>  
> -		uh = packet_get(in, i, sizeof(*eh) + hlen, sizeof(*uh), NULL);
> +		uh = IOV_PEEK_HEADER(&data, uh_storage);
>  		if (!uh)
>  			continue;
>  
>  		if (iph->protocol == IPPROTO_UDP) {
> +			struct iov_tail eh_data;
> +
>  			PACKET_POOL_P(pkt, 1, in->buf, in->buf_size);
>  
> -			data = IOV_TAIL_FROM_BUF((void *)eh, l2len, 0);
> -			packet_add(pkt, &data);
> +			packet_data(in, i, &eh_data);
> +			packet_add(pkt, &eh_data);
>  			if (dhcp(c, pkt))
>  				continue;
>  		}
> @@ -834,7 +842,6 @@ resume:
>  #undef L4_SET
>  
>  append:
> -		data = IOV_TAIL_FROM_BUF((void *)l4h, l4len, 0);
>  		packet_add((struct pool *)&seq->p, &data);
>  	}
>  

-- 
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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