- Rotate the lease file when running in v6 mode.

[ISC-Bugs #24887]

RELNOTES

@@ -147,6 +147,11 @@ work on other platforms. Please report any problems and suggested fixes to
   The use of a boolean test instead of a bitwise test in dst.
   [ISC-Bugs #28941]
 
+- Rotate the lease file when running in v6 mode.
+  Thanks to Christoph Moench-Tegeder at Astaro for the
+  report and the first version of the patch.
+  [ISC-Bugs #24887]
+
 			Changes since 4.2.2
 
 - Fix the code that checks for an existing DDNS transaction to cancel

includes/dhcpd.h

@@ -2761,6 +2761,7 @@ int write_billing_class (struct class *);
 void commit_leases_timeout (void *);
 void commit_leases_readerdry(void *);
 int commit_leases (void);
+int commit_leases_timed (void);
 void db_startup (int);
 int new_lease_file (void);
 int group_writer (struct group_object *);

server/db.c

@@ -36,6 +36,8 @@
 #include <ctype.h>
 #include <errno.h>
 
+#define LEASE_REWRITE_PERIOD 3600
+
 static isc_result_t write_binding_scope(FILE *db_file, struct binding *bnd,
 					char *prepend);
 
@@ -1002,7 +1004,7 @@ int commit_leases ()
 	/* If we haven't rewritten the lease database in over an
 	   hour, rewrite it now.  (The length of time should probably
 	   be configurable. */
-	if (count && cur_time - write_time > 3600) {
+	if (count && cur_time - write_time > LEASE_REWRITE_PERIOD) {
 		count = 0;
 		write_time = cur_time;
 		new_lease_file ();
@@ -1010,6 +1012,21 @@ int commit_leases ()
 	return 1;
 }
 
+/*
+ * rewrite the lease file about once an hour
+ * This is meant as a quick patch for ticket 24887.  It allows
+ * us to rotate the v6 lease file without adding too many fsync()
+ * calls.  In the future wes should revisit this area and add
+ * something similar to the delayed ack code for v4.
+ */
+int commit_leases_timed()
+{
+	if ((count != 0) && (cur_time - write_time > LEASE_REWRITE_PERIOD)) {
+		return (commit_leases());
+	}
+	return (1);
+}
+
 void db_startup (testp)
 	int testp;
 {

server/dhcpv6.c

@@ -1207,6 +1207,10 @@ pick_v6_prefix(struct iasubopt **pref, int plen,
 }
 
 /*
+ *! \file server/dhcpv6.c
+ *
+ * \brief construct a reply containing information about a client's lease
+ *
  * lease_to_client() is called from several messages to construct a
  * reply that contains all that we know about the client's correct lease
  * (or projected lease).
@@ -1228,8 +1232,15 @@ pick_v6_prefix(struct iasubopt **pref, int plen,
  * validate and echo back any contents that can be.  If the client-supplied
  * data does not error out (on renew/rebind as above), but we did not send
  * any addresses, attempt to allocate one.
+ *
+ * At the end of the this function we call commit_leases_timed() to
+ * fsync and rotate the file as necessary.  commit_leases_timed() will
+ * check that we have written at least one lease to the file and that
+ * some time has passed before doing any fsync or file rewrite so we
+ * don't bother tracking if we did a write_ia during this function.
  */
 /* TODO: look at client hints for lease times */
+
 static void
 lease_to_client(struct data_string *reply_ret,
 		struct packet *packet, 
@@ -1493,6 +1504,9 @@ lease_to_client(struct data_string *reply_ret,
 	memcpy(reply_ret->buffer->data, reply.buf.data, reply.cursor);
 	reply_ret->data = reply_ret->buffer->data;
 
+	/* If appropriate commit and rotate the lease file */
+	(void) commit_leases_timed();
+
       exit:
 	/* Cleanup. */
 	if (reply.shared != NULL)

server/mdb6.c

@@ -1714,6 +1714,13 @@ lease_timeout_support(void *vpool) {
 		iasubopt_dereference(&lease, MDL);
 	}
 
+	/*
+	 * If appropriate commit and rotate the lease file
+	 * As commit_leases_timed() checks to see if we've done any writes
+	 * we don't bother tracking if this function called write _ia
+	 */
+	(void) commit_leases_timed();
+
 	/*
 	 * Do some cleanup of our expired leases.
 	 */