Add a perform_ip_subnet_bcast() function that uses Linux netlink sockets

to set the interface ip, subnet, and broadcast address simultaneously.

The advantage of this approach is that a single netlink notification
will be sent rather than multiple messages as the ip, subnet,
and broadcast address are set one at a time.

Currently this function is not used, as it will require a wire format
change that will be introduced in a subsequent commit.

ifchd/linux.c

@@ -40,6 +40,8 @@
 #include <net/route.h>
 #include <net/if.h>
 #include <netpacket/packet.h>
+#include <linux/netlink.h>
+#include <linux/rtnetlink.h>
 #include <pwd.h>
 #include <grp.h>
 
@@ -151,6 +153,192 @@ static int set_if_flag(struct ifchd_client *cl, short flag)
     return ret;
 }
 
+#define NLMSG_TAIL(nmsg)                               \
+    ((struct rtattr *) (((uint8_t*) (nmsg)) +          \
+                        NLMSG_ALIGN((nmsg)->nlmsg_len)))
+
+static int add_rtattr(struct nlmsghdr *n, size_t max_length, int type,
+                      const void *data, size_t data_length)
+{
+    size_t length;
+    struct rtattr *rta;
+
+    length = RTA_LENGTH(data_length);
+
+    if (NLMSG_ALIGN(n->nlmsg_len) + RTA_ALIGN(length) > max_length)
+        return -E2BIG;
+
+    rta = NLMSG_TAIL(n);
+    rta->rta_type = type;
+    rta->rta_len = length;
+    memcpy(RTA_DATA(rta), data, data_length);
+    n->nlmsg_len = NLMSG_ALIGN(n->nlmsg_len) + RTA_ALIGN(length);
+
+    return 0;
+}
+
+static int get_ifindex(const char *name)
+{
+    struct ifreq ifr;
+    int sk, err;
+
+    if (!name)
+        return -1;
+
+    sk = socket(PF_INET, SOCK_DGRAM, 0);
+    if (sk < 0)
+        return -1;
+
+    memset(&ifr, 0, sizeof ifr);
+    strnkcpy(ifr.ifr_name, name, sizeof ifr.ifr_name);
+
+    err = ioctl(sk, SIOCGIFINDEX, &ifr);
+    close(sk);
+    if (err < 0)
+        return -1;
+
+    return ifr.ifr_ifindex;
+}
+
+// 32-bit position values are relatively prime to 37, so the residue mod37
+// gives a unique mapping for each value.  Gives correct result for v=0.
+static int trailz(uint32_t v)
+{
+    static const int bpm37[] = {
+        32, 0, 1, 26, 2, 23, 27, 0, 3, 16, 24, 30, 28, 11, 0, 13, 4, 7, 17,
+        0, 25, 22, 31, 15, 29, 10, 12, 6, 0, 21, 14, 9, 5, 20, 8, 19, 18
+    };
+    return bpm37[(-v & v) % 37];
+}
+
+// sn must be in network order
+static inline int subnet4_to_prefixlen(uint32_t sn)
+{
+    return 32 - trailz(sn);
+}
+
+// str_bcast is optional.
+void perform_ip_subnet_bcast(struct ifchd_client *cl,
+                             const char *str_ipaddr,
+                             const char *str_subnet,
+                             const char *str_bcast)
+{
+    uint8_t request[NLMSG_ALIGN(sizeof(struct nlmsghdr)) +
+        NLMSG_ALIGN(sizeof(struct ifaddrmsg)) +
+        RTA_LENGTH(sizeof(struct in6_addr))];
+    struct in_addr ipaddr, subnet, bcast;
+    struct sockaddr_nl nl_addr;
+    struct nlmsghdr *header;
+    struct ifaddrmsg *ifaddrmsg;
+    int nls, ifidx, r;
+    uint8_t prefixlen;
+
+    if (!str_ipaddr) {
+        log_line("%s: (%s) interface ip address is NULL",
+                 cl->ifnam, __func__);
+        return;
+    }
+    if (!str_subnet) {
+        log_line("%s: (%s) interface subnet address is NULL",
+                 cl->ifnam, __func__);
+        return;
+    }
+
+    if (!is_permitted(cl->ifnam))
+        return;
+    ifidx = get_ifindex(cl->ifnam);
+    if (ifidx < 0) {
+        log_line("%s: (%s) can't get interface index",
+                 cl->ifnam, __func__);
+        return;
+    }
+
+    if (inet_pton(AF_INET, str_ipaddr, &ipaddr) <= 0) {
+        log_line("%s: (%s) bad interface ip address: '%s'",
+                 cl->ifnam, __func__, str_ipaddr);
+        return;
+    }
+
+    if (inet_pton(AF_INET, str_subnet, &subnet) <= 0) {
+        log_line("%s: (%s) bad interface subnet address: '%s'",
+                 cl->ifnam, __func__, str_subnet);
+        return;
+    }
+    prefixlen = subnet4_to_prefixlen(subnet.s_addr);
+
+    if (str_bcast) {
+        if (inet_pton(AF_INET, str_bcast, &bcast) <= 0) {
+            log_line("%s: (%s) bad interface broadcast address: '%s'",
+                     cl->ifnam, __func__, str_bcast);
+            return;
+        }
+    } else {
+        // Generate the standard broadcast address if unspecified.
+        bcast.s_addr = ipaddr.s_addr | htonl(0xfffffffflu >> prefixlen);
+    }
+
+    memset(&request, 0, sizeof request);
+    header = (struct nlmsghdr *)request;
+    header->nlmsg_len = NLMSG_LENGTH(sizeof(struct ifaddrmsg));
+    header->nlmsg_type = RTM_NEWADDR;
+    header->nlmsg_flags = NLM_F_REPLACE | NLM_F_ACK | NLM_F_REQUEST;
+    header->nlmsg_seq = 1;
+
+    ifaddrmsg = NLMSG_DATA(header);
+    ifaddrmsg->ifa_family = AF_INET;
+    ifaddrmsg->ifa_prefixlen = prefixlen;
+    ifaddrmsg->ifa_flags = IFA_F_PERMANENT;
+    ifaddrmsg->ifa_scope = RT_SCOPE_UNIVERSE;
+    ifaddrmsg->ifa_index = ifidx;
+
+    if (add_rtattr(header, sizeof request, IFA_LOCAL,
+                   &ipaddr, sizeof ipaddr) < 0) {
+        log_line("%s: (%s) couldn't add IFA_LOCAL to nlmsg",
+                 cl->ifnam, __func__);
+        return;
+    }
+    if (add_rtattr(header, sizeof request, IFA_BROADCAST,
+                   &bcast, sizeof bcast) < 0) {
+        log_line("%s: (%s) couldn't add IFA_BROADCAST to nlmsg",
+                 cl->ifnam, __func__);
+        return;
+    }
+
+    nls = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE);
+    if (nls < 0) {
+        log_line("%s: (%s) netlink socket open failed: %s",
+                 cl->ifnam, __func__, strerror(errno));
+        return;
+    }
+
+    memset(&nl_addr, 0, sizeof nl_addr);
+    nl_addr.nl_family = AF_NETLINK;
+
+retry_sendto:
+    r = sendto(nls, request, header->nlmsg_len, 0,
+               (struct sockaddr *)&nl_addr, sizeof nl_addr);
+    if (r < 0) {
+        if (errno == EINTR)
+            goto retry_sendto;
+        else {
+            log_line("%s: (%s) netlink sendto socket failed: %s",
+                     cl->ifnam, __func__, strerror(errno));
+            close(nls);
+            return;
+        }
+    }
+    close(nls);
+    log_line("Interface IP set to: '%s'", str_ipaddr);
+    log_line("Interface subnet set to: '%s'", str_subnet);
+    if (str_bcast)
+        log_line("Broadcast address set to: '%s'", str_bcast);
+
+    // XXX: Would be nice to do this via netlink, too.
+    if (set_if_flag(cl, (IFF_UP | IFF_RUNNING)))
+        return;
+}
+
+
 /* Sets IP address on an interface and brings it up. */
 void perform_ip(struct ifchd_client *cl, const char *str, size_t len)
 {