Implementing SIOCGIFNAME for Linuxulator.

Design notes:
- use a separated counter 'ethno' to keep the number of ether devices
  rather than mixing it up with 'index' or the result will be inconsistent
  with linprocfs/net/dev.  Consider the following example:

	$ ifconfig | grep '^[a-z]'
	em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
	ath0: flags=8802<BROADCAST,SIMPLEX,MULTICAST> metric 0 mtu 2290
	lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384
	wlan0: flags=8802<BROADCAST,SIMPLEX,MULTICAST> metric 0 mtu 1500

  Doing a Linux ioctl(SIOCGIFNAME) with ifr.ifr_ifindex from 1 ~ 4 on the
above system will yield: eth0, ath0, lo0 and eth1(the correct behaviour).
On the other hand, if one removes ethno and uses index instead, the result
will be: eth0, ath0, lo0 and eth3.

- According to Linux's if.h, ifr_ifru.ifru_metric should be renamed to
  ifr_ifru.ifru_ivalue.  Given that there is no in-kernel consumer of
  l_ifreq::ifr_ifru.ifru_metric, it may be safe for us to introduce
  ifr_ifru.ifru_ivalue and turn ifr_ifru.ifru_metric into an alias of
  ifru_ivalue in a separated commit.

Reviewed by:	kib, marcel

Index: amd64/linux32/linux.h
===================================================================
--- amd64/linux32/linux.h	(revision 254893)
+++ amd64/linux32/linux.h	(working copy)
@@ -654,6 +654,11 @@
 
 #define	ifr_name	ifr_ifrn.ifrn_name	/* Interface name */
 #define	ifr_hwaddr	ifr_ifru.ifru_hwaddr	/* MAC address */
+/*
+ * XXX: In Linux, there is no ifr_ifru.ifru_metric but a ifr_ifru.ifru_ivalue
+ * instead.  For now we just keep our own naming to avoid API breakage.
+ */
+#define	ifr_ifindex	ifr_ifru.ifru_metric	/* Interface index */
 
 struct l_ifconf {
 	int	ifc_len;
Index: compat/linux/linux_ioctl.c
===================================================================
--- compat/linux/linux_ioctl.c	(revision 254893)
+++ compat/linux/linux_ioctl.c	(working copy)
@@ -2157,6 +2157,49 @@
 }
 
 /*
+ * Implement the SIOCGIFNAME ioctl
+ */
+
+static int
+linux_ioctl_ifname(struct thread *td, struct l_ifreq *uifr)
+{
+	struct l_ifreq ifr;
+	struct ifnet *ifp;
+	int error, ethno, index;
+
+	error = copyin(uifr, &ifr, sizeof(ifr));
+	if (error != 0)
+		return (error);
+
+	CURVNET_SET(TD_TO_VNET(curthread));
+	IFNET_RLOCK();
+	index = 1;	/* ifr.ifr_ifindex starts from 1 */
+	ethno = 0;
+	error = ENODEV;
+	TAILQ_FOREACH(ifp, &V_ifnet, if_link) {
+		if (ifr.ifr_ifindex == index) {
+			if (IFP_IS_ETH(ifp))
+				snprintf(ifr.ifr_name, LINUX_IFNAMSIZ,
+				    "eth%d", ethno);
+			else
+				strlcpy(ifr.ifr_name, ifp->if_xname,
+				    LINUX_IFNAMSIZ);
+			error = 0;
+			break;
+		}
+		if (IFP_IS_ETH(ifp))
+			ethno++;
+		index++;
+	}
+	IFNET_RUNLOCK();
+	if (error == 0)
+        	error = copyout(&ifr, uifr, sizeof(ifr));
+	CURVNET_RESTORE();
+
+	return (error);
+}
+
+/*
  * Implement the SIOCGIFCONF ioctl
  */
 
@@ -2381,6 +2424,7 @@
 	case LINUX_SIOCADDMULTI:
 	case LINUX_SIOCATMARK:
 	case LINUX_SIOCDELMULTI:
+	case LINUX_SIOCGIFNAME:
 	case LINUX_SIOCGIFCONF:
 	case LINUX_SIOCGPGRP:
 	case LINUX_SIOCSPGRP:
@@ -2466,6 +2510,10 @@
 
 	/* LINUX_SIOCGSTAMP */
 
+	case LINUX_SIOCGIFNAME:
+		error = linux_ioctl_ifname(td, (struct l_ifreq *)args->arg);
+		break;
+
 	case LINUX_SIOCGIFCONF:
 		error = linux_ifconf(td, (struct ifconf *)args->arg);
 		break;
Index: compat/linux/linux_ioctl.h
===================================================================
--- compat/linux/linux_ioctl.h	(revision 254893)
+++ compat/linux/linux_ioctl.h	(working copy)
@@ -226,6 +226,7 @@
 #define	LINUX_SIOCGPGRP		0x8904
 #define	LINUX_SIOCATMARK	0x8905
 #define	LINUX_SIOCGSTAMP	0x8906
+#define	LINUX_SIOCGIFNAME	0x8910
 #define	LINUX_SIOCGIFCONF	0x8912
 #define	LINUX_SIOCGIFFLAGS	0x8913
 #define	LINUX_SIOCGIFADDR	0x8915
Index: i386/linux/linux.h
===================================================================
--- i386/linux/linux.h	(revision 254893)
+++ i386/linux/linux.h	(working copy)
@@ -630,6 +630,11 @@
 
 #define	ifr_name	ifr_ifrn.ifrn_name	/* Interface name */
 #define	ifr_hwaddr	ifr_ifru.ifru_hwaddr	/* MAC address */
+/*
+ * XXX: In Linux, there is no ifr_ifru.ifru_metric but a ifr_ifru.ifru_ivalue
+ * instead.  For now we just keep our own naming to avoid API breakage.
+ */
+#define	ifr_ifindex	ifr_ifru.ifru_metric	/* Interface index */
 
 /*
  * poll()