add hostsfile output in addition to statefile

a92c0a7 made the temporary state/leasefile hidden so that an atomic
change was made and dnsmasq only saw the new file on rename.  A
misguided optimisation was made to only rename the temporary file if
something had changed.  Unfortunately only address and hostnames were
considered in the change, lease durations were not.

As a result it was possible for LUCI which consumes the state/leasefile
to report DHCPv6 leases had expired when they had not.

Revert the optimisation so that the file rename occurs irrespective of
content change, this keeps LUCI reporting of state/lease expiry correct.

This leaves us back with hosts file/dnsmasq update problem. Solve this
by writing out a separate hosts file.  Update this file using the
original IP/Hostname change logic that prompts calling the 'lease'
script.

odhcpd config now supports a string 'hostsfile' which defines the path
and name of the hosts file in an identical manner to 'leasefile'.  A
state 'leasefile' must be defined IF a 'hostsfile' is also required.

eg.

leasefile '/tmp/odhcpdstate'
hostsfile '/tmp/hosts/odhcpdhosts'

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>

4 files changed, 127 insertions, 4 deletions

diff --git a/README b/README
index 8f0e6a4..243ae24 100644
--- a/README
+++ b/README
@@ -64,6 +64,7 @@ maindhcp	bool	0			Use odhcpd as the main DHCPv4
 						service
 leasefile	string				DHCP/v6 lease/hostfile
 leasetrigger	string				Lease trigger script
+hostsfile	string				DHCP/v6 hostfile
 loglevel	integer 6			Syslog level priority (0-7)
 
 
diff --git a/src/config.c b/src/config.c
index e631814..5ba4d9e 100644
--- a/src/config.c
+++ b/src/config.c
@@ -29,7 +29,7 @@ static void lease_update(struct vlist_tree *tree, struct vlist_node *node_new,
 struct vlist_tree leases = VLIST_TREE_INIT(leases, lease_cmp, lease_update, true, false);
 AVL_TREE(interfaces, avl_strcmp, false, NULL);
 struct config config = {.legacy = false, .main_dhcpv4 = false,
-			.dhcp_cb = NULL, .dhcp_statefile = NULL,
+			.dhcp_cb = NULL, .dhcp_statefile = NULL, .dhcp_hostsfile = NULL,
 			.log_level = LOG_WARNING};
 
 #define START_DEFAULT	100
@@ -180,6 +180,7 @@ enum {
 	ODHCPD_ATTR_LEASEFILE,
 	ODHCPD_ATTR_LEASETRIGGER,
 	ODHCPD_ATTR_LOGLEVEL,
+	ODHCPD_ATTR_HOSTSFILE,
 	ODHCPD_ATTR_MAX
 };
 
@@ -189,6 +190,7 @@ static const struct blobmsg_policy odhcpd_attrs[ODHCPD_ATTR_MAX] = {
 	[ODHCPD_ATTR_LEASEFILE] = { .name = "leasefile", .type = BLOBMSG_TYPE_STRING },
 	[ODHCPD_ATTR_LEASETRIGGER] = { .name = "leasetrigger", .type = BLOBMSG_TYPE_STRING },
 	[ODHCPD_ATTR_LOGLEVEL] = { .name = "loglevel", .type = BLOBMSG_TYPE_INT32 },
+	[ODHCPD_ATTR_HOSTSFILE] = { .name = "hostsfile", .type = BLOBMSG_TYPE_STRING },
 };
 
 const struct uci_blob_param_list odhcpd_attr_list = {
@@ -326,6 +328,11 @@ static void set_config(struct uci_section *s)
 		config.dhcp_statefile = strdup(blobmsg_get_string(c));
 	}
 
+	if ((c = tb[ODHCPD_ATTR_HOSTSFILE])) {
+		free(config.dhcp_hostsfile);
+		config.dhcp_hostsfile = strdup(blobmsg_get_string(c));
+	}
+
 	if ((c = tb[ODHCPD_ATTR_LEASETRIGGER])) {
 		free(config.dhcp_cb);
 		config.dhcp_cb = strdup(blobmsg_get_string(c));
diff --git a/src/dhcpv6-ia.c b/src/dhcpv6-ia.c
index 41c9f30..1fbed44 100644
--- a/src/dhcpv6-ia.c
+++ b/src/dhcpv6-ia.c
@@ -288,6 +288,26 @@ struct write_ctxt {
 	int buf_idx;
 };
 
+static void dhcpv6_write_ia_addrhosts(struct in6_addr *addr, int prefix, _unused uint32_t pref,
+				_unused uint32_t valid, void *arg)
+{
+	struct write_ctxt *ctxt = (struct write_ctxt *)arg;
+	char ipbuf[INET6_ADDRSTRLEN];
+
+	if ((ctxt->c->flags & OAF_DHCPV6_NA) && ctxt->c->hostname &&
+	    !(ctxt->c->flags & OAF_BROKEN_HOSTNAME)) {
+		inet_ntop(AF_INET6, addr, ipbuf, sizeof(ipbuf) - 1);
+		fputs(ipbuf, ctxt->fp);
+
+		char b[256];
+		if (dn_expand(ctxt->iface->search, ctxt->iface->search + ctxt->iface->search_len,
+				ctxt->iface->search, b, sizeof(b)) > 0)
+			fprintf(ctxt->fp, "\t%s.%s", ctxt->c->hostname, b);
+
+		fprintf(ctxt->fp, "\t%s\n", ctxt->c->hostname);
+	}
+}
+
 static void dhcpv6_write_ia_addr(struct in6_addr *addr, int prefix, _unused uint32_t pref,
 				_unused uint32_t valid, void *arg)
 {
@@ -314,6 +334,98 @@ static void dhcpv6_write_ia_addr(struct in6_addr *addr, int prefix, _unused uint
 					"%s/%d ", ipbuf, prefix);
 }
 
+static void dhcpv6_ia_write_hostsfile(time_t now)
+{
+	struct write_ctxt ctxt;
+
+	unsigned hostsfile_strlen = strlen(config.dhcp_hostsfile) + 1;
+	unsigned tmp_hostsfile_strlen = hostsfile_strlen + 1; /* space for . */
+	char *tmp_hostsfile = alloca(tmp_hostsfile_strlen);
+
+	char *dir_hostsfile;
+	char *base_hostsfile;
+	char *pdir_hostsfile;
+	char *pbase_hostsfile;
+
+	int fd, ret;
+
+	dir_hostsfile = strndup(config.dhcp_hostsfile, hostsfile_strlen);
+	base_hostsfile = strndup(config.dhcp_hostsfile, hostsfile_strlen);
+
+	pdir_hostsfile = dirname(dir_hostsfile);
+	pbase_hostsfile = basename(base_hostsfile);
+
+	snprintf(tmp_hostsfile, tmp_hostsfile_strlen, "%s/.%s", pdir_hostsfile, pbase_hostsfile);
+
+	free(dir_hostsfile);
+	free(base_hostsfile);
+
+	fd = open(tmp_hostsfile, O_CREAT | O_WRONLY | O_CLOEXEC, 0644);
+	if (fd < 0)
+		return;
+
+	ret = lockf(fd, F_LOCK, 0);
+	if (ret < 0) {
+		close(fd);
+		return;
+	}
+
+	if (ftruncate(fd, 0) < 0) {}
+
+	ctxt.fp = fdopen(fd, "w");
+	if (!ctxt.fp) {
+		close(fd);
+		return;
+	}
+
+	avl_for_each_element(&interfaces, ctxt.iface, avl) {
+		if (ctxt.iface->dhcpv6 != MODE_SERVER &&
+				ctxt.iface->dhcpv4 != MODE_SERVER)
+			continue;
+
+		if (ctxt.iface->dhcpv6 == MODE_SERVER) {
+			list_for_each_entry(ctxt.c, &ctxt.iface->ia_assignments, head) {
+				if (!(ctxt.c->flags & OAF_BOUND) || ctxt.c->managed_size < 0)
+					continue;
+
+				if (INFINITE_VALID(ctxt.c->valid_until) || ctxt.c->valid_until > now)
+					dhcpv6_ia_enum_addrs(ctxt.iface, ctxt.c, now,
+								dhcpv6_write_ia_addrhosts, &ctxt);
+			}
+		}
+
+		if (ctxt.iface->dhcpv4 == MODE_SERVER) {
+			struct dhcp_assignment *c;
+
+			list_for_each_entry(c, &ctxt.iface->dhcpv4_assignments, head) {
+				if (!(c->flags & OAF_BOUND))
+					continue;
+
+				char ipbuf[INET6_ADDRSTRLEN];
+				struct in_addr addr = {.s_addr = c->addr};
+				inet_ntop(AF_INET, &addr, ipbuf, sizeof(ipbuf) - 1);
+
+				if (c->hostname && !(c->flags & OAF_BROKEN_HOSTNAME)) {
+					fputs(ipbuf, ctxt.fp);
+
+					char b[256];
+
+					if (dn_expand(ctxt.iface->search,
+							ctxt.iface->search + ctxt.iface->search_len,
+							ctxt.iface->search, b, sizeof(b)) > 0)
+						fprintf(ctxt.fp, "\t%s.%s", c->hostname, b);
+
+					fprintf(ctxt.fp, "\t%s\n", c->hostname);
+				}
+			}
+		}
+	}
+
+	fclose(ctxt.fp);
+
+	rename(tmp_hostsfile, config.dhcp_hostsfile);
+}
+
 void dhcpv6_ia_write_statefile(void)
 {
 	struct write_ctxt ctxt;
@@ -457,9 +569,13 @@ void dhcpv6_ia_write_statefile(void)
 		uint8_t newmd5[16];
 		md5_end(newmd5, &ctxt.md5);
 
+		rename(tmp_statefile, config.dhcp_statefile);
+
 		if (memcmp(newmd5, statemd5, sizeof(newmd5))) {
 			memcpy(statemd5, newmd5, sizeof(statemd5));
-			rename(tmp_statefile, config.dhcp_statefile);
+
+			if (config.dhcp_hostsfile)
+				dhcpv6_ia_write_hostsfile(now);
 
 			if (config.dhcp_cb) {
 				char *argv[2] = {config.dhcp_cb, NULL};
@@ -468,8 +584,6 @@ void dhcpv6_ia_write_statefile(void)
 					_exit(128);
 				}
 			}
-		} else {
-			unlink(tmp_statefile);
 		}
 	}
 }
diff --git a/src/odhcpd.h b/src/odhcpd.h
index 08b4920..02b6ac0 100644
--- a/src/odhcpd.h
+++ b/src/odhcpd.h
@@ -165,6 +165,7 @@ struct config {
 	bool main_dhcpv4;
 	char *dhcp_cb;
 	char *dhcp_statefile;
+	char *dhcp_hostsfile;
 	int log_level;
 };