Linux: use broadcast flag with ipvlan interfaces by default.

Linux ipvlan interfaces share a MAC address with their siblings and
parent physical interface.  Before they are assigned an IP address,
these virtual interfaces do not receive DHCP OFFER unicast messages
because the ipvlan driver does not know to pass them to the virtual
interface yet by IP.  This chicken-and-egg problem is resolved with
two changes:

In this patch, we set the broadcast flag for an interface if it
belongs to the ipvlan driver, as detected via SIOCETHTOOL ETHTOOL_GDRVINFO.
(closes #32)

A forthcoming patch will automatically modify the DHCP IAID for
ipvlan interfaces so that they do not conflict with the parent
(lower/physical) interface IAID.  For now, dhcpcd will display a warning
log message when conflicting IAID (same MAC address) interfaces are active.

(A minor grammar correction is included free of charge.)

src/common.h

@@ -63,6 +63,10 @@
 #define ROUNDUP4(a)		(1 + (((a) - 1) |  3))
 #define ROUNDUP8(a)		(1 + (((a) - 1) |  7))
 
+#ifndef FIELD_SIZEOF
+#define FIELD_SIZEOF(t, f) sizeof(((t *)0)->f)
+#endif
+
 /* Some systems don't define timespec macros */
 #ifndef timespecclear
 #define timespecclear(tsp)      (tsp)->tv_sec = (time_t)((tsp)->tv_nsec = 0L)

src/dhcpcd.8.in

@@ -651,7 +651,7 @@ of a randomly generated number.
 .It Fl J , Fl Fl broadcast
 Instructs the DHCP server to broadcast replies back to the client.
 Normally this is only set for non-Ethernet interfaces,
-such as FireWire and InfiniBand.
+such as FireWire and InfiniBand, and on Linux-based systems for ipvlan as well.
 In most instances,
 .Nm
 will set this automatically.

src/dhcpcd.c

@@ -470,7 +470,7 @@ configure_interface1(struct interface *ifp)
 
 	if (!(ifo->options & DHCPCD_IAID)) {
 		/*
-		 * An IAID is for identifying a unqiue interface within
+		 * An IAID is for identifying an unique interface within
 		 * the client. It is 4 bytes long. Working out a default
 		 * value is problematic.
 		 *

src/if-linux.c

@@ -42,6 +42,7 @@
 #include <linux/if_vlan.h>
 #include <linux/filter.h>
 #include <linux/netlink.h>
+#include <linux/ethtool.h> /* for ipvlan detection */
 #include <linux/sockios.h>
 #include <linux/rtnetlink.h>
 
@@ -309,12 +310,55 @@ if_init(struct interface *ifp)
 	return if_writepathuint(ifp->ctx, path, 1) == -1 ? -1 : 0;
 }
 
+/* Returns number of bytes written to driver, else 0 (error or indeterminate). */
+static size_t
+if_get_driver(struct interface *ifp, char *driver, const size_t driverlen)
+{
+	struct ethtool_drvinfo drvinfo = { .cmd = ETHTOOL_GDRVINFO };
+	struct ifreq ifr = { .ifr_data = (void *)&drvinfo };
+
+	strlcpy(ifr.ifr_name, ifp->name, sizeof(ifr.ifr_name));
+	if (ioctl(ifp->ctx->pf_inet_fd, SIOCETHTOOL, &ifr) != 0) {
+		logerr("%s: SIOCETHTOOL ifname=%s", __func__, ifp->name);
+		return 0; /* 0 means error or indeterminate driver name */
+	}
+	return strlcpy(driver, drvinfo.driver, driverlen);
+}
+
+static bool
+if_cmp_driver(struct interface *ifp, const char *driver)
+{
+	char ifdriver[FIELD_SIZEOF(struct ethtool_drvinfo, driver)];
+	size_t n = if_get_driver(ifp, ifdriver, sizeof(ifdriver));
+
+	if (n == 0) {
+		logerr("%s: if_get_driver ifname=%s", __func__, ifp->name);
+		return false;
+	}
+	if (strncmp(ifdriver, driver, n) == 0)
+		return true;
+	return false;
+}
+
+static bool
+if_ipvlan(struct interface *ifp)
+{
+	if (if_cmp_driver(ifp, "ipvlan"))
+		return true;
+	return false;
+}
+
 int
 if_conf(struct interface *ifp)
 {
 	char path[sizeof(SYS_LAYER2) + IF_NAMESIZE];
 	int n;
 
+	/* Set broadcast flag for ipvlan interfaces.
+	 * XXX: move this out to dhcpcd if needed on other platforms. */
+	if (if_ipvlan(ifp))
+		ifp->options->options |= DHCPCD_BROADCAST;
+
 	/* Some qeth setups require the use of the broadcast flag. */
 	snprintf(path, sizeof(path), SYS_LAYER2, ifp->name);
 	n = check_proc_int(ifp->ctx, path);