Reviewed-by: Eugene Crosser <crosser@average.org>

On 28/01/2022 00:06, Pablo Neira Ayuso wrote:
> If interface netlink dump is interrupted, then retry.
> 
> Before this patch, the netlink socket is reopened to drop stale dump
> messages, instead empty the netlink queue and retry.
> 
> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
> ---
> v2: immediately return on non-eintr error (instead of breaking the loop),
>     per Eugene Crosser.
> 
>  src/iface.c | 50 ++++++++++++++++++++++++++++++++++++++------------
>  1 file changed, 38 insertions(+), 12 deletions(-)
> 
> diff --git a/src/iface.c b/src/iface.c
> index d0e1834ca82f..c0642e0cc397 100644
> --- a/src/iface.c
> +++ b/src/iface.c
> @@ -59,13 +59,13 @@ static int data_cb(const struct nlmsghdr *nlh, void *data)
>  	return MNL_CB_OK;
>  }
>  
> -void iface_cache_update(void)
> +static int iface_mnl_talk(struct mnl_socket *nl, uint32_t portid)
>  {
>  	char buf[MNL_SOCKET_BUFFER_SIZE];
> -	struct mnl_socket *nl;
>  	struct nlmsghdr *nlh;
>  	struct rtgenmsg *rt;
> -	uint32_t seq, portid;
> +	bool eintr = false;
> +	uint32_t seq;
>  	int ret;
>  
>  	nlh = mnl_nlmsg_put_header(buf);
> @@ -75,6 +75,38 @@ void iface_cache_update(void)
>  	rt = mnl_nlmsg_put_extra_header(nlh, sizeof(struct rtgenmsg));
>  	rt->rtgen_family = AF_PACKET;
>  
> +	if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0)
> +		return -1;
> +
> +	ret = mnl_socket_recvfrom(nl, buf, sizeof(buf));
> +	while (ret > 0) {
> +		ret = mnl_cb_run(buf, ret, seq, portid, data_cb, NULL);
> +		if (ret == 0)
> +			break;
> +		if (ret < 0) {
> +			if (errno != EINTR)
> +				return ret;
> +
> +			/* process all pending messages before reporting EINTR */
> +			eintr = true;
> +		}
> +		ret = mnl_socket_recvfrom(nl, buf, sizeof(buf));
> +	}
> +
> +	if (eintr) {
> +		ret = -1;
> +		errno = EINTR;
> +	}
> +
> +	return ret;
> +}
> +
> +void iface_cache_update(void)
> +{
> +	struct mnl_socket *nl;
> +	uint32_t portid;
> +	int ret;
> +
>  	nl = mnl_socket_open(NETLINK_ROUTE);
>  	if (nl == NULL)
>  		netlink_init_error();
> @@ -84,16 +116,10 @@ void iface_cache_update(void)
>  
>  	portid = mnl_socket_get_portid(nl);
>  
> -	if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0)
> -		netlink_init_error();
> +	do {
> +		ret = iface_mnl_talk(nl, portid);
> +	} while (ret < 0 && errno == EINTR);
>  
> -	ret = mnl_socket_recvfrom(nl, buf, sizeof(buf));
> -	while (ret > 0) {
> -		ret = mnl_cb_run(buf, ret, seq, portid, data_cb, NULL);
> -		if (ret <= MNL_CB_STOP)
> -			break;
> -		ret = mnl_socket_recvfrom(nl, buf, sizeof(buf));
> -	}
>  	if (ret == -1)
>  		netlink_init_error();
>