leaseshelper: improvements to support all events

This patch enables the helper program to detect event(s) triggered when
there is a change in lease length or expiry and client-id. This
transfers complete control of leases database to libvirt and obsoletes
use of the lease database file (<network-name>.leases). That file will
not be created, read, or written.  This is achieved by adding the option
--leasefile-ro to dnsmasq and passing a custom env var to leaseshelper,
which helps us map events related to leases with their corresponding
network bridges, no matter what the event be.

Also, this requires the addition of a new non-lease entry in our custom
lease database: "server-duid". It is required to identify a DHCPv6
server.

Now that dnsmasq doesn't maintain its own leases database, it relies on
our helper program to tell it about previous leases and server duid.
Thus, this patch makes our leases program honor an extra action: "init",
in which it sends the known info in a particular format to dnsmasq
by printing it to stdout.

The drawback of this change is that upgrade to this new approach does
not transfer the existing leases for the network if the leaseshelper
wasn't already used.

src/network/bridge_driver.c

@@ -1299,7 +1299,10 @@ networkBuildDhcpDaemonCommandLine(virNetworkObjPtr network,
 
     cmd = virCommandNew(dnsmasqCapsGetBinaryPath(caps));
     virCommandAddArgFormat(cmd, "--conf-file=%s", configfile);
+    /* Libvirt gains full control of leases database */
+    virCommandAddArgFormat(cmd, "--leasefile-ro");
     virCommandAddArgFormat(cmd, "--dhcp-script=%s", leaseshelper_path);
+    virCommandAddEnvPair(cmd, "VIR_BRIDGE_NAME", network->def->bridge);
 
     *cmdout = cmd;
     ret = 0;

src/network/leaseshelper.c

@@ -50,6 +50,12 @@
  */
 #define VIR_NETWORK_DHCP_LEASE_FILE_SIZE_MAX (32 * 1024 * 1024)
 
+/*
+ * Use this when passing possibly-NULL strings to printf-a-likes.
+ * Required for unknown parameters during init call.
+ */
+#define EMPTY_STR(s) ((s) ? (s) : "*")
+
 static const char *program_name;
 
 /* Display version information. */
@@ -65,7 +71,7 @@ usage(int status)
     if (status) {
         fprintf(stderr, _("%s: try --help for more details\n"), program_name);
     } else {
-        printf(_("Usage: %s add|old|del mac|clientid ip [hostname]\n"
+        printf(_("Usage: %s add|old|del|init mac|clientid ip [hostname]\n"
                  "Designed for use with 'dnsmasq --dhcp-script'\n"
                  "Refer to man page of dnsmasq for more details'\n"),
                program_name);
@@ -89,6 +95,7 @@ enum virLeaseActionFlags {
     VIR_LEASE_ACTION_ADD,       /* Create new lease */
     VIR_LEASE_ACTION_OLD,       /* Lease already exists, renew it */
     VIR_LEASE_ACTION_DEL,       /* Delete the lease */
+    VIR_LEASE_ACTION_INIT,      /* Tell dnsmasq of existing leases on restart */
 
     VIR_LEASE_ACTION_LAST
 };
@@ -96,7 +103,7 @@ enum virLeaseActionFlags {
 VIR_ENUM_DECL(virLeaseAction);
 
 VIR_ENUM_IMPL(virLeaseAction, VIR_LEASE_ACTION_LAST,
-              "add", "old", "del");
+              "add", "old", "del", "init");
 
 int
 main(int argc, char **argv)
@@ -107,12 +114,15 @@ main(int argc, char **argv)
     char *custom_lease_file = NULL;
     const char *ip = NULL;
     const char *mac = NULL;
+    const char *ip_tmp = NULL;
+    const char *leases_str = NULL;
+    const char *server_duid_tmp = NULL;
     const char *iaid = virGetEnvAllowSUID("DNSMASQ_IAID");
     const char *clientid = virGetEnvAllowSUID("DNSMASQ_CLIENT_ID");
     const char *interface = virGetEnvAllowSUID("DNSMASQ_INTERFACE");
     const char *exptime_tmp = virGetEnvAllowSUID("DNSMASQ_LEASE_EXPIRES");
     const char *hostname = virGetEnvAllowSUID("DNSMASQ_SUPPLIED_HOSTNAME");
-    const char *leases_str = NULL;
+    const char *server_duid = virGetEnvAllowSUID("DNSMASQ_SERVER_DUID");
     long long currtime = 0;
     long long expirytime = 0;
     size_t i = 0;
@@ -120,7 +130,6 @@ main(int argc, char **argv)
     int pid_file_fd = -1;
     int rv = EXIT_FAILURE;
     int custom_lease_file_len = 0;
-    bool add = false;
     bool delete = false;
     virJSONValuePtr lease_new = NULL;
     virJSONValuePtr lease_tmp = NULL;
@@ -156,16 +165,17 @@ main(int argc, char **argv)
         }
     }
 
-    if (argc != 4 && argc != 5) {
+    if (argc != 4 && argc != 5 && argc != 2) {
         /* Refer man page of dnsmasq --dhcp-script for more details */
         usage(EXIT_FAILURE);
     }
 
     /* Make sure dnsmasq knows the interface. The interface name is not known
-     * when dnsmasq (re)starts and throws 'del' events for expired leases.
-     * So, if any old lease has expired, it will be automatically removed the
-     * next time this program is invoked */
-    if (!interface)
+     * via env variable set by dnsmasq when dnsmasq (re)starts and throws 'del'
+     * events for expired leases. So, libvirtd sets another env var for this
+     * purpose */
+    if (!interface &&
+        !(interface = virGetEnvAllowSUID("VIR_BRIDGE_NAME")))
         goto cleanup;
 
     ip = argv[3];
@@ -176,15 +186,22 @@ main(int argc, char **argv)
     if (argc == 5)
         hostname = argv[4];
 
-    if (VIR_STRDUP(exptime, exptime_tmp) < 0)
-        goto cleanup;
+    /* In case hostname is still unknown, use the last known one */
+    if (!hostname)
+        hostname = virGetEnvAllowSUID("DNSMASQ_OLD_HOSTNAME");
 
-    /* Removed extraneous trailing space in DNSMASQ_LEASE_EXPIRES (dnsmasq < 2.52) */
-    if (exptime[strlen(exptime) - 1] == ' ')
-        exptime[strlen(exptime) - 1] = '\0';
+    if (exptime_tmp) {
+        if (VIR_STRDUP(exptime, exptime_tmp) < 0)
+            goto cleanup;
+
+        /* Removed extraneous trailing space in DNSMASQ_LEASE_EXPIRES
+         * (dnsmasq < 2.52) */
+        if (exptime[strlen(exptime) - 1] == ' ')
+            exptime[strlen(exptime) - 1] = '\0';
+    }
 
     /* Check if it is an IPv6 lease */
-    if (virGetEnvAllowSUID("DNSMASQ_IAID")) {
+    if (iaid) {
         mac = virGetEnvAllowSUID("DNSMASQ_MAC");
         clientid = argv[2];
     }
@@ -234,7 +251,6 @@ main(int argc, char **argv)
             delete = true;
             if (action == VIR_LEASE_ACTION_ADD ||
                 action == VIR_LEASE_ACTION_OLD) {
-                add = true;
                 /* Create new lease */
                 if (!(lease_new = virJSONValueNewObject())) {
                     virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
@@ -242,10 +258,11 @@ main(int argc, char **argv)
                     goto cleanup;
                 }
 
-                if (virStrToLong_ll(exptime, NULL, 10, &expirytime) < 0) {
+                if (!exptime ||
+                    virStrToLong_ll(exptime, NULL, 10, &expirytime) < 0) {
                     virReportError(VIR_ERR_INTERNAL_ERROR,
                                    _("Unable to convert lease expiry time to long long: %s"),
-                                   exptime);
+                                   NULLSTR(exptime));
                     goto cleanup;
                 }
 
@@ -259,11 +276,13 @@ main(int argc, char **argv)
                     goto cleanup;
                 if (clientid && virJSONValueObjectAppendString(lease_new, "client-id", clientid) < 0)
                     goto cleanup;
+                if (server_duid && virJSONValueObjectAppendString(lease_new, "server-duid", server_duid) < 0)
+                    goto cleanup;
                 if (expirytime && virJSONValueObjectAppendNumberLong(lease_new, "expiry-time", expirytime) < 0)
                     goto cleanup;
             }
         }
-    } else {
+    } else if (action != VIR_LEASE_ACTION_INIT) {
         fprintf(stderr, _("Unsupported action: %s\n"),
                 virLeaseActionTypeToString(action));
         exit(EXIT_FAILURE);
@@ -292,8 +311,6 @@ main(int argc, char **argv)
 
             i = 0;
             while (i < virJSONValueArraySize(leases_array)) {
-                const char *ip_tmp = NULL;
-                long long expirytime_tmp = -1;
 
                 if (!(lease_tmp = virJSONValueArrayGet(leases_array, i))) {
                     virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
@@ -302,14 +319,13 @@ main(int argc, char **argv)
                 }
 
                 if (!(ip_tmp = virJSONValueObjectGetString(lease_tmp, "ip-address")) ||
-                    (virJSONValueObjectGetNumberLong(lease_tmp, "expiry-time", &expirytime_tmp) < 0)) {
+                    (virJSONValueObjectGetNumberLong(lease_tmp, "expiry-time", &expirytime) < 0)) {
                     virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                                    _("failed to parse json"));
                     goto cleanup;
                 }
-
                 /* Check whether lease has expired or not */
-                if (expirytime_tmp < currtime) {
+                if (expirytime < currtime) {
                     i++;
                     continue;
                 }
@@ -320,6 +336,25 @@ main(int argc, char **argv)
                     continue;
                 }
 
+                if (strchr(ip_tmp, ':')) {
+                    /* This is an ipv6 lease */
+                    if ((server_duid_tmp
+                         = virJSONValueObjectGetString(lease_tmp, "server-duid"))) {
+                        if (!server_duid) {
+                            /* Control reaches here when the 'action' is not for an
+                             * ipv6 lease or, for some weird reason the env var
+                             * DNSMASQ_SERVER_DUID wasn't set*/
+                            server_duid = server_duid_tmp;
+                        }
+                    } else {
+                        /* Inject server-duid into those ipv6 leases which
+                         * didn't have it previously, for example, those
+                         * created by leaseshelper from libvirt 1.2.6 */
+                        if (virJSONValueObjectAppendString(lease_tmp, "server-duid", server_duid) < 0)
+                            goto cleanup;
+                    }
+                }
+
                 /* Move old lease to new array */
                 if (virJSONValueArrayAppend(leases_array_new, lease_tmp) < 0) {
                     virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
@@ -332,25 +367,80 @@ main(int argc, char **argv)
         }
     }
 
-    if (add) {
+    switch ((enum virLeaseActionFlags) action) {
+    case VIR_LEASE_ACTION_INIT:
+        /* Man page of dnsmasq says: the script (helper program, in our case)
+         * should write the saved state of the lease database, in dnsmasq
+         * leasefile format, to stdout and exit with zero exit code, when
+         * called with argument init. Format:
+         * $expirytime $mac $ip $hostname $clientid # For all ipv4 leases
+         * duid $server-duid # If DHCPv6 is present
+         * $expirytime $iaid $ip $hostname $clientduid # For all ipv6 leases */
+
+        /* Traversing the ipv4 leases */
+        for (i = 0; i < virJSONValueArraySize(leases_array_new); i++) {
+            lease_tmp = virJSONValueArrayGet(leases_array_new, i);
+            if (!(ip_tmp = virJSONValueObjectGetString(lease_tmp, "ip-address"))) {
+                virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                               _("failed to parse json"));
+                goto cleanup;
+            }
+            if (!strchr(ip_tmp, ':')) {
+                virJSONValueObjectGetNumberLong(lease_tmp, "expiry-time", &expirytime);
+                printf("%lld %s %s %s %s\n",
+                       expirytime,
+                       virJSONValueObjectGetString(lease_tmp, "mac-address"),
+                       virJSONValueObjectGetString(lease_tmp, "ip-address"),
+                       EMPTY_STR(virJSONValueObjectGetString(lease_tmp, "hostname")),
+                       EMPTY_STR(virJSONValueObjectGetString(lease_tmp, "client-id")));
+            }
+        }
+
+        /* Traversing the ipv6 leases */
+        if (server_duid) {
+            printf("duid %s\n", server_duid);
+            for (i = 0; i < virJSONValueArraySize(leases_array_new); i++) {
+                lease_tmp = virJSONValueArrayGet(leases_array_new, i);
+                if (!(ip_tmp = virJSONValueObjectGetString(lease_tmp, "ip-address"))) {
+                    virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                                   _("failed to parse json"));
+                    goto cleanup;
+                }
+                if (strchr(ip_tmp, ':')) {
+                    virJSONValueObjectGetNumberLong(lease_tmp, "expiry-time", &expirytime);
+                    printf("%lld %s %s %s %s\n",
+                           expirytime,
+                           virJSONValueObjectGetString(lease_tmp, "iaid"),
+                           virJSONValueObjectGetString(lease_tmp, "ip-address"),
+                           EMPTY_STR(virJSONValueObjectGetString(lease_tmp, "hostname")),
+                           EMPTY_STR(virJSONValueObjectGetString(lease_tmp, "client-id")));
+                }
+            }
+        }
+
+        break;
+
+    case VIR_LEASE_ACTION_OLD:
+    case VIR_LEASE_ACTION_ADD:
         if (virJSONValueArrayAppend(leases_array_new, lease_new) < 0) {
             virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                            _("failed to create json"));
             goto cleanup;
         }
         lease_new = NULL;
-    }
 
-    if (!(leases_str = virJSONValueToString(leases_array_new, true))) {
-        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                       _("empty json array"));
-        goto cleanup;
-    }
+    default:
+        if (!(leases_str = virJSONValueToString(leases_array_new, true))) {
+            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                           _("empty json array"));
+            goto cleanup;
+        }
 
-    /* Write to file */
-    if (virFileRewrite(custom_lease_file, 0644,
-                       customLeaseRewriteFile, &leases_str) < 0)
-        goto cleanup;
+        /* Write to file */
+        if (virFileRewrite(custom_lease_file, 0644,
+                           customLeaseRewriteFile, &leases_str) < 0)
+            goto cleanup;
+    }
 
     rv = EXIT_SUCCESS;