Utility functions to produce an IPv4 broadcast address

These functions work only for IPv4, becasue IPv6 doesn't have the same
concept of "broadcast address" as IPv4. They merely OR the inverse of
the netmask with the given host address, thus turning on all the host
bits.

src/libvirt_private.syms

@@ -558,6 +558,8 @@ virShrinkN;
 
 
 # network.h
+virSocketAddrBroadcast;
+virSocketAddrBroadcastByPrefix;
 virSocketAddrIsNetmask;
 virSocketAddrMask;
 virSocketAddrMaskByPrefix;

src/util/network.c

@@ -340,6 +340,61 @@ virSocketAddrMaskByPrefix(virSocketAddrPtr addr, unsigned int prefix)
     return virSocketAddrMask(addr, &netmask);
 }
 
+/**
+ * virSocketAddrBroadcast:
+ * @addr: address that needs to be turned into broadcast address (IPv4 only)
+ * @netmask: the netmask address
+ * @broadcast: virSocketAddr to recieve the broadcast address
+ *
+ * Mask ON the host bits of @addr according to @netmask, turning it
+ * into a broadcast address.
+ *
+ * Returns 0 in case of success, or -1 on error.
+ */
+int
+virSocketAddrBroadcast(const virSocketAddrPtr addr,
+                       const virSocketAddrPtr netmask,
+                       virSocketAddrPtr       broadcast)
+{
+    if ((addr->data.stor.ss_family != AF_INET) ||
+        (netmask->data.stor.ss_family != AF_INET)) {
+        broadcast->data.stor.ss_family = AF_UNSPEC;
+        return -1;
+    }
+
+    broadcast->data.stor.ss_family = AF_INET;
+    broadcast->len = addr->len;
+    broadcast->data.inet4.sin_addr.s_addr
+        = (addr->data.inet4.sin_addr.s_addr
+           | ~netmask->data.inet4.sin_addr.s_addr);
+    return 0;
+}
+
+/**
+ * virSocketAddrBroadcastByPrefix:
+ * @addr: address that needs to be turned into broadcast address (IPv4 only)
+ * @prefix: prefix (# of 1 bits) of netmask to apply
+ * @broadcast: virSocketAddr to recieve the broadcast address
+ *
+ * Mask off the host bits of @addr according to @prefix, turning it
+ * into a network address.
+ *
+ * Returns 0 in case of success, or -1 on error.
+ */
+int
+virSocketAddrBroadcastByPrefix(const virSocketAddrPtr addr,
+                               unsigned int           prefix,
+                               virSocketAddrPtr       broadcast)
+{
+    virSocketAddr netmask;
+
+    if (virSocketAddrPrefixToNetmask(prefix, &netmask,
+                                     addr->data.stor.ss_family) < 0)
+        return -1;
+
+    return virSocketAddrBroadcast(addr, &netmask, broadcast);
+}
+
 /**
  * virSocketCheckNetmask:
  * @addr1: a first network address

src/util/network.h

@@ -77,6 +77,12 @@ int virSocketAddrMask     (virSocketAddrPtr addr,
                            const virSocketAddrPtr netmask);
 int virSocketAddrMaskByPrefix(virSocketAddrPtr addr,
                               unsigned int prefix);
+int virSocketAddrBroadcast(const virSocketAddrPtr addr,
+                           const virSocketAddrPtr netmask,
+                           virSocketAddrPtr       broadcast);
+int virSocketAddrBroadcastByPrefix(const virSocketAddrPtr addr,
+                                   unsigned int           prefix,
+                                   virSocketAddrPtr       broadcast);
 
 int virSocketGetNumNetmaskBits(const virSocketAddrPtr netmask);
 int virSocketAddrPrefixToNetmask(unsigned int prefix,