virnetdevtap: add virNetDevTapGetName

This will be used on a tap file descriptor returned by the bridge helper
to populate the <target> element, because the helper does not provide
the interface name.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

src/libvirt_private.syms

@@ -1533,6 +1533,7 @@ virNetDevOpenvswitchSetMigrateData;
 virNetDevTapCreate;
 virNetDevTapCreateInBridgePort;
 virNetDevTapDelete;
+virNetDevTapGetName;
 
 
 # util/virnetdevveth.h

src/util/virnetdevtap.c

@@ -42,6 +42,40 @@
 
 #define VIR_FROM_THIS VIR_FROM_NONE
 
+/**
+ * virNetDevTapGetName:
+ * @tapfd: a tun/tap file descriptor
+ * @ifname: a pointer that will receive the interface name
+ *
+ * Retrieve the interface name given a file descriptor for a tun/tap
+ * interface.
+ *
+ * Returns 0 if the interface name is successfully queried, -1 otherwise
+ */
+int
+virNetDevTapGetName(int tapfd, char **ifname)
+{
+#ifdef TUNGETIFF
+    struct ifreq ifr;
+
+    if (ioctl(tapfd, TUNGETIFF, &ifr) < 0) {
+        virReportSystemError(errno, "%s",
+                             _("Unable to query tap interface name"));
+        return -1;
+    }
+
+    *ifname = strdup(ifr.ifr_name);
+    if (*ifname == NULL) {
+        virReportOOMError();
+        return -1;
+    }
+    return 0;
+#else
+    return -1;
+#endif
+}
+
+
 /**
  * virNetDevProbeVnetHdr:
  * @tapfd: a tun/tap file descriptor

src/util/virnetdevtap.h

@@ -35,6 +35,9 @@ int virNetDevTapCreate(char **ifname,
 int virNetDevTapDelete(const char *ifname)
     ATTRIBUTE_NONNULL(1) ATTRIBUTE_RETURN_CHECK;
 
+int virNetDevTapGetName(int tapfd, char **ifname)
+    ATTRIBUTE_NONNULL(2) ATTRIBUTE_RETURN_CHECK;
+
 typedef enum {
    VIR_NETDEV_TAP_CREATE_NONE = 0,
    /* Bring the interface up */