Re: [PATCH 06/14] Add helpers for normal inbound packet destination addresses

[Stefano Brivio <sbrivio@redhat.com>]

On Mon, 17 Oct 2022 19:57:59 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> tap_ip_send() doesn't take a destination address, because it's specifically
> for inbound packets, and the IP addresses of the guest/namespace are
> already known to us.  Rather than open-coding this destination address
> logic, make helper functions for it which will enable some later cleanups.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  tap.c | 29 ++++++++++++++++++++++++-----
>  tap.h |  3 +++
>  2 files changed, 27 insertions(+), 5 deletions(-)
> 
> diff --git a/tap.c b/tap.c
> index de02c56..41e8ff2 100644
> --- a/tap.c
> +++ b/tap.c
> @@ -96,6 +96,28 @@ int tap_send(const struct ctx *c, const void *data, size_t len, int vnet_pre)
>  	return write(c->fd_tap, (char *)data + (vnet_pre ? 4 : 0), len);
>  }
>  
> +/**
> + * tap_ip4_daddr() - Normal IPv4 destination address for inbound packets
> + * @c:		Execution context

Given that the address is returned in network order, I think this would
be relevant here:

 * Return: IPv4 address, network order

> + */
> +in_addr_t tap_ip4_daddr(const struct ctx *c)
> +{
> +	return c->ip4.addr_seen;
> +}
> +
> +/**
> + * tap_ip6_daddr() - Normal IPv4 destination address for inbound packets
> + * @c:		Execution context
> + * @src:	Source address

 * Return: pointer to IPv6 address

> + */
> +const struct in6_addr *tap_ip6_daddr(const struct ctx *c,
> +				     const struct in6_addr *src)
> +{
> +	if (IN6_IS_ADDR_LINKLOCAL(src))
> +		return &c->ip6.addr_ll_seen;
> +	return &c->ip6.addr_seen;
> +}
> +
>  /**
>   * tap_ip_send() - Send IP packet, with L2 headers, calculating L3/L4 checksums
>   * @c:		Execution context
> @@ -132,7 +154,7 @@ void tap_ip_send(const struct ctx *c, const struct in6_addr *src, uint8_t proto,
>  		iph->frag_off = 0;
>  		iph->ttl = 255;
>  		iph->protocol = proto;
> -		iph->daddr = c->ip4.addr_seen;
> +		iph->daddr = tap_ip4_daddr(c);
>  		memcpy(&iph->saddr, &src->s6_addr[12], 4);
>  
>  		csum_ip4_header(iph);
> @@ -163,10 +185,7 @@ void tap_ip_send(const struct ctx *c, const struct in6_addr *src, uint8_t proto,
>  		ip6h->priority = 0;
>  
>  		ip6h->saddr = *src;
> -		if (IN6_IS_ADDR_LINKLOCAL(src))
> -			ip6h->daddr = c->ip6.addr_ll_seen;
> -		else
> -			ip6h->daddr = c->ip6.addr_seen;
> +		ip6h->daddr = *tap_ip6_daddr(c, src);
>  
>  		memcpy(data, in, len);
>  
> diff --git a/tap.h b/tap.h
> index df3aec0..a6764b4 100644
> --- a/tap.h
> +++ b/tap.h
> @@ -6,6 +6,9 @@
>  #ifndef TAP_H
>  #define TAP_H
>  
> +in_addr_t tap_ip4_daddr(const struct ctx *c);
> +const struct in6_addr *tap_ip6_daddr(const struct ctx *c,
> +				     const struct in6_addr *src);
>  void tap_ip_send(const struct ctx *c, const struct in6_addr *src, uint8_t proto,
>  		 const char *in, size_t len, uint32_t flow);
>  int tap_send(const struct ctx *c, const void *data, size_t len, int vnet_pre);

-- 
Stefano