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[libvirt] [PATCH] leaseshelper: add enhancements 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 suppresses 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 applying
the symlink technique, which helps us map events related to leases with their
corresponding network bridges.
Example:
/var/lib/libvirt/dnsmasq/virbr0.helper -> /home/wani/libvirt/src/libvirt_leaseshelper
/var/lib/libvirt/dnsmasq/virbr3.helper -> /home/wani/libvirt/src/libvirt_leaseshelper

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.

---
 src/network/bridge_driver.c |  43 +++++++++++-
 src/network/leaseshelper.c  | 156 +++++++++++++++++++++++++++++++++++++-------
 2 files changed, 175 insertions(+), 24 deletions(-)

diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c
index 6a2e760..1e1e53f 100644
--- a/src/network/bridge_driver.c
+++ b/src/network/bridge_driver.c
@@ -229,6 +229,16 @@ networkDnsmasqLeaseFileNameCustom(const char *bridge)
 }
 
 static char *
+networkDnsmasqPseudoLeaseHelperName(const char *bridge)
+{
+    char *pseudo_leasehelper;
+
+    ignore_value(virAsprintf(&pseudo_leasehelper, "%s/%s.helper",
+                             driverState->dnsmasqStateDir, bridge));
+    return pseudo_leasehelper;
+}
+
+static char *
 networkDnsmasqConfigFileName(const char *netname)
 {
     char *conffile;
@@ -1261,6 +1271,7 @@ networkBuildDhcpDaemonCommandLine(virNetworkObjPtr network,
     char *configfile = NULL;
     char *configstr = NULL;
     char *leaseshelper_path = NULL;
+    char *pseudo_leaseshelper_path = NULL;
 
     network->dnsmasqPid = -1;
 
@@ -1273,6 +1284,11 @@ networkBuildDhcpDaemonCommandLine(virNetworkObjPtr network,
     if (!(configfile = networkDnsmasqConfigFileName(network->def->name)))
         goto cleanup;
 
+    /* construct symlink name */
+    if (!(pseudo_leaseshelper_path
+          = networkDnsmasqPseudoLeaseHelperName(network->def->bridge)))
+        goto cleanup;
+
     /* Write the file */
     if (virFileWriteStr(configfile, configstr, 0600) < 0) {
         virReportSystemError(errno,
@@ -1287,9 +1303,30 @@ networkBuildDhcpDaemonCommandLine(virNetworkObjPtr network,
                                                   LIBEXECDIR)))
         goto cleanup;
 
+    /* Symlink technique for dnsmasq lease file is needed so that libvirt
+     * can have complete control over the handling of leases database */
+
+    /* Remove unwanted, old symlink */
+    if (unlink(pseudo_leaseshelper_path) < 0 &&
+        errno != ENOENT && errno != ENOTDIR) {
+        virReportSystemError(errno,
+                             _("Failed to delete symlink '%s'"),
+                             pseudo_leaseshelper_path);
+        goto cleanup;
+    }
+
+    /* Create a new symlink */
+    if (symlink(leaseshelper_path, pseudo_leaseshelper_path) < 0) {
+        virReportSystemError(errno,
+                             _("Failed to create symlink '%s' to '%s'"),
+                             leaseshelper_path, pseudo_leaseshelper_path);
+        goto cleanup;
+    }
+
     cmd = virCommandNew(dnsmasqCapsGetBinaryPath(caps));
     virCommandAddArgFormat(cmd, "--conf-file=%s", configfile);
-    virCommandAddArgFormat(cmd, "--dhcp-script=%s", leaseshelper_path);
+    virCommandAddArgFormat(cmd, "--dhcp-script=%s", pseudo_leaseshelper_path);
+    virCommandAddArgFormat(cmd, "--leasefile-ro");
 
     *cmdout = cmd;
     ret = 0;
@@ -3432,6 +3469,10 @@ networkGetDHCPLeases(virNetworkPtr network,
             goto error;
         }
 
+        /* Ignore server-duid. It's not part of a lease */
+        if (virJSONValueObjectHasKey(lease_tmp, "server-duid"))
+            continue;
+
         if (!(mac_tmp = virJSONValueObjectGetString(lease_tmp, "mac-address"))) {
             /* leaseshelper program guarantees that lease will be stored only if
              * mac-address is known otherwise not */
diff --git a/src/network/leaseshelper.c b/src/network/leaseshelper.c
index e4b5283..3d6c773 100644
--- a/src/network/leaseshelper.c
+++ b/src/network/leaseshelper.c
@@ -50,6 +50,13 @@
  */
 #define VIR_NETWORK_DHCP_LEASE_FILE_SIZE_MAX (32 * 1024 * 1024)
 
+/*
+ * Use this when passing possibly-NULL strings to printf-a-likes.
+ * Required for unkown parameters during init call.
+ */
+# define EMPTY_STR(s) ((s) ? (s) : "*")
+
+
 static const char *program_name;
 
 /* Display version information. */
@@ -65,7 +72,7 @@ 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 +96,7 @@ 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 +104,7 @@ 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)
@@ -105,6 +113,7 @@ main(int argc, char **argv)
     char *pid_file = NULL;
     char *lease_entries = NULL;
     char *custom_lease_file = NULL;
+    char *server_duid = NULL;
     const char *ip = NULL;
     const char *mac = NULL;
     const char *iaid = virGetEnvAllowSUID("DNSMASQ_IAID");
@@ -112,20 +121,26 @@ main(int argc, char **argv)
     const char *interface = virGetEnvAllowSUID("DNSMASQ_INTERFACE");
     const char *exptime_tmp = virGetEnvAllowSUID("DNSMASQ_LEASE_EXPIRES");
     const char *hostname = virGetEnvAllowSUID("DNSMASQ_SUPPLIED_HOSTNAME");
+    const char *server_duid_env = virGetEnvAllowSUID("DNSMASQ_SERVER_DUID");
     const char *leases_str = NULL;
     long long currtime = 0;
     long long expirytime = 0;
     size_t i = 0;
+    size_t count_ipv6 = 0;
+    size_t count_ipv4 = 0;
     int action = -1;
     int pid_file_fd = -1;
     int rv = EXIT_FAILURE;
     int custom_lease_file_len = 0;
     bool add = false;
+    bool init = false;
     bool delete = false;
     virJSONValuePtr lease_new = NULL;
     virJSONValuePtr lease_tmp = NULL;
     virJSONValuePtr leases_array = NULL;
     virJSONValuePtr leases_array_new = NULL;
+    virJSONValuePtr *leases_ipv4 = NULL;
+    virJSONValuePtr *leases_ipv6 = NULL;
 
     virSetErrorFunc(NULL, NULL);
     virSetErrorLogPriorityFunc(NULL);
@@ -156,17 +171,19 @@ 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)
-        goto cleanup;
+     * via env variable when dnsmasq (re)starts and throws 'del' events for
+     * expired leases. Our symlink hack provides us an alternative method to
+     * find it */
+    if (!interface) {
+        interface = basename(argv[0]);
+       *(strchr(interface, '.')) = '\0';
+    }
 
     ip = argv[3];
     mac = argv[2];
@@ -185,9 +202,14 @@ main(int argc, char **argv)
         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];
+
+        if (server_duid_env) {
+            if (VIR_STRDUP(server_duid, server_duid_env) < 0)
+                goto cleanup;
+        }
     }
 
     if (virAsprintf(&custom_lease_file,
@@ -264,6 +286,8 @@ main(int argc, char **argv)
                     goto cleanup;
             }
         }
+    } else if (action == VIR_LEASE_ACTION_INIT) {
+        init = true;
     } else {
         fprintf(stderr, _("Unsupported action: %s\n"),
                 virLeaseActionTypeToString(action));
@@ -294,6 +318,7 @@ main(int argc, char **argv)
             i = 0;
             while (i < virJSONValueArraySize(leases_array)) {
                 const char *ip_tmp = NULL;
+                const char *server_duid_tmp = NULL;
                 long long expirytime_tmp = -1;
 
                 if (!(lease_tmp = virJSONValueArrayGet(leases_array, i))) {
@@ -302,6 +327,20 @@ main(int argc, char **argv)
                     goto cleanup;
                 }
 
+                if ((server_duid_tmp
+                     = virJSONValueObjectGetString(lease_tmp, "server-duid"))) {
+                    /* Control reaches here atmost once */
+                    if (!server_duid) {
+                        /* Control reaches here when the action is not for an
+                         * ipv6 lease or for some weird reason the env variable
+                         * DNSMASQ_SERVER_DUID wasn't set*/
+                        if (VIR_STRDUP(server_duid, server_duid_tmp) < 0)
+                            goto cleanup;
+                    }
+                    i++;
+                    continue;
+                }
+
                 if (!(ip_tmp = virJSONValueObjectGetString(lease_tmp, "ip-address")) ||
                     (virJSONValueObjectGetNumberLong(lease_tmp, "expiry-time", &expirytime_tmp) < 0)) {
                     virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
@@ -328,39 +367,110 @@ main(int argc, char **argv)
                     goto cleanup;
                 }
 
+                /* Store pointers to ipv4 and ipv6 leases */
+                if (strchr(ip_tmp, ':'))
+                    ignore_value(VIR_APPEND_ELEMENT(leases_ipv6, count_ipv6, lease_tmp));
+                else
+                    ignore_value(VIR_APPEND_ELEMENT(leases_ipv4, count_ipv4, lease_tmp));
+
                 ignore_value(virJSONValueArraySteal(leases_array, i));
             }
         }
     }
 
-    if (add) {
-        if (virJSONValueArrayAppend(leases_array_new, lease_new) < 0) {
+    if (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:
+         * #For all ipv4 leases:
+         * Expiry_time MAC_address IP_address Hostname Client-id
+         * #If DHCPv6 is present:
+         * duid Server_DUID
+         * #For all ipv6 leases:
+         * Expiry_time IAID IP_address Hostname Client-DUID */
+        long long expirytime_tmp = -1;
+        for (i = 0; i < count_ipv4; i++) {
+            lease_tmp = leases_ipv4[i];
+            virJSONValueObjectGetNumberLong(lease_tmp, "expiry-time", &expirytime_tmp);
+            printf("%lld %s %s %s %s\n",
+                   expirytime_tmp,
+                   virJSONValueObjectGetString(lease_tmp, "mac-address"),
+                   virJSONValueObjectGetString(lease_tmp, "ip-address"),
+                   EMPTY_STR(virJSONValueObjectGetString(lease_tmp, "hostname")),
+                   EMPTY_STR(virJSONValueObjectGetString(lease_tmp, "client-id")));
+        }
+        if (server_duid) {
+            printf("duid %s\n", server_duid);
+            for (i = 0; i < count_ipv6; i++) {
+                lease_tmp = leases_ipv6[i];
+                virJSONValueObjectGetNumberLong(lease_tmp, "expiry-time", &expirytime_tmp);
+                printf("%lld %s %s %s %s\n",
+                       expirytime_tmp,
+                       virJSONValueObjectGetString(lease_tmp, "iaid"),
+                       virJSONValueObjectGetString(lease_tmp, "ip-address"),
+                       EMPTY_STR(virJSONValueObjectGetString(lease_tmp, "hostname")),
+                       EMPTY_STR(virJSONValueObjectGetString(lease_tmp, "client-id")));
+            }
+        }
+    }
+    else {
+        if (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 (server_duid) {
+            if (!(lease_new = virJSONValueNewObject())) {
+                virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                               _("failed to create json"));
+                goto cleanup;
+            }
+
+            if (virJSONValueObjectAppendString(lease_new,
+                                               "server-duid", server_duid) < 0)
+                goto cleanup;
+
+            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",
-                           _("failed to create json"));
+                           _("empty json array"));
             goto cleanup;
         }
-        lease_new = NULL;
-    }
 
-    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;
 
  cleanup:
     if (pid_file_fd != -1)
         virPidFileReleasePath(pid_file, pid_file_fd);
 
+    for (i = 0; i < count_ipv4; i++)
+        VIR_FREE(leases_ipv4);
+
+    for (i = 0; i < count_ipv6; i++)
+        VIR_FREE(leases_ipv6);
+
     VIR_FREE(pid_file);
     VIR_FREE(exptime);
+    VIR_FREE(server_duid);
+    VIR_FREE(lease_entries);
     VIR_FREE(custom_lease_file);
     virJSONValueFree(lease_new);
     virJSONValueFree(leases_array);
-- 
1.9.3


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