1 files changed, 102 insertions, 0 deletions
diff --git a/src/core/dnsmasq/nm-dnsmasq-utils.c b/src/core/dnsmasq/nm-dnsmasq-utils.c
new file mode 100644
index 00000000..ea23a78d
--- /dev/null
+++ b/src/core/dnsmasq/nm-dnsmasq-utils.c
@@ -0,0 +1,102 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2013 Red Hat, Inc.
+ */
+
+#include "src/core/nm-default-daemon.h"
+
+#include <arpa/inet.h>
+
+#include "nm-dnsmasq-utils.h"
+#include "platform/nm-platform.h"
+#include "nm-utils.h"
+
+gboolean
+nm_dnsmasq_utils_get_range(const NMPlatformIP4Address *addr,
+                           char *                      out_first,
+                           char *                      out_last,
+                           char **                     out_error_desc)
+{
+    guint32       host   = addr->address;
+    guint8        prefix = addr->plen;
+    guint32       netmask;
+    guint32       first, last, mid, reserved;
+    const guint32 NUM = 256;
+
+    g_return_val_if_fail(out_first, FALSE);
+    g_return_val_if_fail(out_last, FALSE);
+
+    if (prefix > 30) {
+        if (out_error_desc)
+            *out_error_desc = g_strdup_printf("Address prefix %d is too small for DHCP.", prefix);
+        return FALSE;
+    }
+
+    if (prefix < 24) {
+        /* if the subnet is larger then /24, we partition it and treat it
+         * like it would be a /24.
+         *
+         * Hence, the resulting range will always be between x.x.x.1/24
+         * and x.x.x.254/24, with x.x.x.0 being the network address of the
+         * host.
+         *
+         * In this case, only a /24 portion of the subnet is used.
+         * No particular reason for that, but it's unlikely that a user
+         * would use NetworkManager's shared method when having hundred
+         * of DHCP clients. So, restrict the range to the same /24 in
+         * which the host address lies.
+         */
+        prefix = 24;
+    }
+
+    netmask = _nm_utils_ip4_prefix_to_netmask(prefix);
+
+    /* treat addresses in host-order from here on. */
+    netmask = ntohl(netmask);
+    host    = ntohl(host);
+
+    /* if host is the network or broadcast address, coerce it to
+     * one above or below. Usually, we wouldn't expect the user
+     * to pick such an address. */
+    if (host == (host & netmask))
+        host++;
+    else if (host == (host | ~netmask))
+        host--;
+
+    /* Exclude the network and broadcast address. */
+    first = (host & netmask) + 1;
+    last  = (host | ~netmask) - 1;
+
+    /* Depending on whether host is above or below the middle of
+     * the subnet, the larger part if handed out.
+     *
+     * If the host is in the lower half, the range starts
+     * at the lower end with the host (plus reserved), until the
+     * broadcast address
+     *
+     * If the host is in the upper half, the range starts above
+     * the network-address and goes up until the host (except reserved).
+     *
+     * reserved is up to 8 addresses, 10% of the determined range.
+     */
+    mid = (host & netmask) | (((first + last) / 2) & ~netmask);
+    if (host > mid) {
+        /* use lower range */
+        reserved = NM_MIN(((host - first) / 10), 8);
+        last     = host - 1 - reserved;
+        first    = NM_MAX(first, last > NUM ? last - NUM : 0);
+    } else {
+        /* use upper range */
+        reserved = NM_MIN(((last - host) / 10), 8);
+        first    = host + 1 + reserved;
+        last     = NM_MIN(last, first < 0xFFFFFFFF - NUM ? first + NUM : 0xFFFFFFFF);
+    }
+
+    first = htonl(first);
+    last  = htonl(last);
+
+    _nm_utils_inet4_ntop(first, out_first);
+    _nm_utils_inet4_ntop(last, out_last);
+
+    return TRUE;
+}