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

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 15 Aug 2024 13:04:42 +1000
David Gibson <david@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@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