Re: [PATCH 5/7] netlink, pasta: Fetch link-local address from namespace interface once it's up

On Thu, 15 Aug 2024 13:04:42 +1000
David Gibson <david(a)gibson.dropbear.id.au> wrote:

...
  On Thu, Aug 15, 2024 at 12:54:27AM +0200, Stefano
Brivio wrote:
  As soon as we bring up the interface, the Linux
kernel will set up a
 link-local address for it, so we can fetch it and start using right
 away, if we need a link-local address to communicate to the container
 before we see any traffic coming from it.
 
 Signed-off-by: Stefano Brivio <sbrivio(a)redhat.com>
 ---
  netlink.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
  netlink.h |  1 +
  pasta.c   |  7 +++++++
  3 files changed, 55 insertions(+)
 
 diff --git a/netlink.c b/netlink.c
 index 4b49de1..3b37087 100644
 --- a/netlink.c
 +++ b/netlink.c
 @@ -836,6 +836,53 @@ int nl_addr_get(int s, unsigned int ifi, sa_family_t af,
  	return status;
  }
  
 +/**
 + * nl_addr_get_ll() - Get first IPv6 link-local address for a given interface
 + * @s:		Netlink socket
 + * @ifi:	Interface index in outer network namespace
 + * @addr:	Link-local address to fill
 + *
 + * Return: 0 on success, negative error code on failure
 + */
 +int nl_addr_get_ll(int s, unsigned int ifi, void *addr)   
 
 Given this is explicitly for IPv6, I don't see a reason not to use
 (struct in6_addr *addr) for greater type safety. 
I'll change that.

...
 
  +{
 +	struct req_t {
 +		struct nlmsghdr nlh;
 +		struct ifaddrmsg ifa;
 +	} req = {
 +		.ifa.ifa_family		= AF_INET6,
 +		.ifa.ifa_index		= ifi,
 +	};
 +	struct nlmsghdr *nh;
 +	bool found = false;
 +	char buf[NLBUFSIZ];
 +	ssize_t status;
 +	uint32_t seq;
 +
 +	seq = nl_send(s, &req, RTM_GETADDR, NLM_F_DUMP, sizeof(req));
 +	nl_foreach_oftype(nh, status, s, buf, seq, RTM_NEWADDR) {
 +		struct ifaddrmsg *ifa = (struct ifaddrmsg *)NLMSG_DATA(nh);
 +		struct rtattr *rta;
 +		size_t na;
 +
 +		if (ifa->ifa_index != ifi || ifa->ifa_scope != RT_SCOPE_LINK ||
 +		    found)
 +			continue;
 +
 +		for (rta = IFA_RTA(ifa), na = IFA_PAYLOAD(nh); RTA_OK(rta, na);
 +		     rta = RTA_NEXT(rta, na)) {
 +			if (rta->rta_type != IFA_ADDRESS)
 +				continue;
 +
 +			if (!found) {
 +				memcpy(addr, RTA_DATA(rta), RTA_PAYLOAD(rta));
 +				found = true;
 +			}
 +		}
 +	}
 +	return status;
 +}
 +
  /**
   * nl_add_set() - Set IP addresses for given interface and address family
   * @s:		Netlink socket
 diff --git a/netlink.h b/netlink.h
 index 66a44ad..bdfdef0 100644
 --- a/netlink.h
 +++ b/netlink.h
 @@ -19,6 +19,7 @@ int nl_addr_get(int s, unsigned int ifi, sa_family_t af,
  		void *addr, int *prefix_len, void *addr_l);
  int nl_addr_set(int s, unsigned int ifi, sa_family_t af,
  		const void *addr, int prefix_len);
 +int nl_addr_get_ll(int s, unsigned int ifi, void *addr);
  int nl_addr_set_ll_nodad(int s, unsigned int ifi);
  int nl_addr_dup(int s_src, unsigned int ifi_src,
  		int s_dst, unsigned int ifi_dst, sa_family_t af);
 diff --git a/pasta.c b/pasta.c
 index 838bbb3..cebf54f 100644
 --- a/pasta.c
 +++ b/pasta.c
 @@ -340,6 +340,13 @@ void pasta_ns_conf(struct ctx *c)
  		}
  
  		if (c->ifi6) {
 +			rc = nl_addr_get_ll(nl_sock_ns, c->pasta_ifi,
 +					    &c->ip6.addr_ll_seen);
 +			if (rc < 0) {
 +				die("Can't fetch LL address from namespace: %s",
 +				    strerror(-rc));   
 
 Again, we can generally cope with not having an addr_ll_seen
 initially, so I think a warn() would make more sense. 
Of course. I'll fix this as well.

-- 
Stefano