libifconfig: allow to get original interface name via ifconfig_get_orig_name()

Uses the same method as in tools/tools/ifinfo/ifinfo.c
(via net.link.generic sysctl).

Tested with modified wlandebug(8).

Differential Revision:	https://reviews.freebsd.org/D12554

lib/libifconfig/libifconfig.c

@@ -61,9 +61,43 @@
  * $FreeBSD$
  */
 
+ /*
+ * Copyright 1996 Massachusetts Institute of Technology
+ *
+ * Permission to use, copy, modify, and distribute this software and
+ * its documentation for any purpose and without fee is hereby
+ * granted, provided that both the above copyright notice and this
+ * permission notice appear in all copies, that both the above
+ * copyright notice and this permission notice appear in all
+ * supporting documentation, and that the name of M.I.T. not be used
+ * in advertising or publicity pertaining to distribution of the
+ * software without specific, written prior permission.  M.I.T. makes
+ * no representations about the suitability of this software for any
+ * purpose.  It is provided "as is" without express or implied
+ * warranty.
+ *
+ * THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''.  M.I.T. DISCLAIMS
+ * ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
+ * SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+ * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#include <sys/types.h>
 #include <sys/ioctl.h>
+#include <sys/sysctl.h>
 
 #include <net/if.h>
+#include <net/if_mib.h>
 
 #include <err.h>
 #include <errno.h>
@@ -247,6 +281,67 @@ ifconfig_set_name(ifconfig_handle_t *h, const char *name, const char *newname)
 	return (0);
 }
 
+int
+ifconfig_get_orig_name(ifconfig_handle_t *h, const char *ifname,
+    char **orig_name)
+{
+	struct ifmibdata ifmd;
+	size_t len;
+	int name[6];
+	int i, maxifno;
+
+	name[0] = CTL_NET;
+	name[1] = PF_LINK;
+	name[2] = NETLINK_GENERIC;
+	name[3] = IFMIB_SYSTEM;
+	name[4] = IFMIB_IFCOUNT;
+
+	len = sizeof maxifno;
+	if (sysctl(name, 5, &maxifno, &len, 0, 0) < 0) {
+		h->error.errtype = OTHER;
+		h->error.errcode = errno;
+		return (-1);
+	}
+
+	name[3] = IFMIB_IFDATA;
+	name[5] = IFDATA_GENERAL;
+	for (i = 1; i <= maxifno; i++) {
+		len = sizeof ifmd;
+		name[4] = i;
+		if (sysctl(name, 6, &ifmd, &len, 0, 0) < 0) {
+			if (errno == ENOENT)
+				continue;
+
+			goto fail;
+		}
+
+		if (strncmp(ifmd.ifmd_name, ifname, IFNAMSIZ) != 0)
+			continue;
+
+		len = 0;
+		name[5] = IFDATA_DRIVERNAME;
+		if (sysctl(name, 6, NULL, &len, 0, 0) < 0)
+			goto fail;
+
+		*orig_name = malloc(len);
+		if (*orig_name == NULL)
+			goto fail;
+
+		if (sysctl(name, 6, *orig_name, &len, 0, 0) < 0) {
+			free(*orig_name);
+			*orig_name = NULL;
+			goto fail;
+		}
+
+		return (0);
+	}
+
+fail:
+	h->error.errtype = OTHER;
+	h->error.errcode = (i <= maxifno) ? errno : ENOENT;
+	return (-1);
+}
+
 int
 ifconfig_set_mtu(ifconfig_handle_t *h, const char *name, const int mtu)
 {

lib/libifconfig/libifconfig.h

@@ -82,6 +82,8 @@ int ifconfig_set_description(ifconfig_handle_t *h, const char *name,
 int ifconfig_unset_description(ifconfig_handle_t *h, const char *name);
 int ifconfig_set_name(ifconfig_handle_t *h, const char *name,
     const char *newname);
+int ifconfig_get_orig_name(ifconfig_handle_t *h, const char *ifname,
+    char **orig_name);
 int ifconfig_set_mtu(ifconfig_handle_t *h, const char *name, const int mtu);
 int ifconfig_get_mtu(ifconfig_handle_t *h, const char *name, int *mtu);
 int ifconfig_set_metric(ifconfig_handle_t *h, const char *name,