Re: [PATCH v2 06/12] icmp: Use -1 to represent "missing" sockets

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 21 Dec 2023 17:53:21 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> icmp_id_map[] contains, amongst other things, fds for "ping" sockets
> associated with various ICMP echo ids.  However, we only lazily open()
> those sockets, so many will be missing.  We currently represent that with
> a 0, which isn't great, since that's technically a valid fd.  Use -1
> instead.  This does require initializing the fields in icmp_id_map[] but
> we already have an obvious place to do that.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  icmp.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/icmp.c b/icmp.c
> index 7a505b4..dd98c7f 100644
> --- a/icmp.c
> +++ b/icmp.c
> @@ -179,7 +179,7 @@ int icmp_tap_handler(const struct ctx *c, uint8_t pif, int af,
>  
>  		iref.id = id = ntohs(ih->un.echo.id);
>  
> -		if ((s = icmp_id_map[V4][id].sock) <= 0) {
> +		if ((s = icmp_id_map[V4][id].sock) < 0) {
>  			s = sock_l4(c, AF_INET, IPPROTO_ICMP, &c->ip4.addr_out,
>  				    c->ip4.ifname_out, 0, iref.u32);
>  			if (s < 0)
> @@ -221,7 +221,7 @@ int icmp_tap_handler(const struct ctx *c, uint8_t pif, int af,
>  			return 1;
>  
>  		iref.id = id = ntohs(ih->icmp6_identifier);
> -		if ((s = icmp_id_map[V6][id].sock) <= 0) {
> +		if ((s = icmp_id_map[V6][id].sock) < 0) {
>  			s = sock_l4(c, AF_INET6, IPPROTO_ICMPV6,
>  				    &c->ip6.addr_out,
>  				    c->ip6.ifname_out, 0, iref.u32);
> @@ -277,7 +277,7 @@ static void icmp_timer_one(const struct ctx *c, int v6, uint16_t id,
>  
>  	epoll_ctl(c->epollfd, EPOLL_CTL_DEL, id_map->sock, NULL);
>  	close(id_map->sock);
> -	id_map->sock = 0;
> +	id_map->sock = -1;
>  	id_map->seq = -1;
>  }
>  
> @@ -315,6 +315,8 @@ void icmp_init(void)
>  {
>  	unsigned i;
>  
> -	for (i = 0; i < ICMP_NUM_IDS; i++)
> +	for (i = 0; i < ICMP_NUM_IDS; i++) {
>  		icmp_id_map[V4][i].seq = icmp_id_map[V6][i].seq = -1;
> +		icmp_id_map[V4][i].sock = icmp_id_map[V6][i].sock = -1;
> +	}

Another (well, kind of existing) use case for a 0xff-initialising
helper.

-- 
Stefano