.conf: don't rely on mtime to determine if service needs reloading

Until now Finit has used mtime to determine if a file has been changed,
or simply touched to request reload, when `initctl reload` is called.
Using mtime for this purpose is a monumentally bad idea since time can
be changed at any point: a user may adjust the time, NTP continously
tunes the clock, and time stamps are stored as the walltime.  So if we
compare timestamps against the last time we (booted or) did reload, we
would miss .conf file changes.

This patch replaces the mtime mistake with an inotify watcher for the
following files: /etc/finit.d/*.conf, /etc/finit.d/available/*.conf,
and /etc/finit.conf.  All file changes between (bootstraps and) calls
to `initctl reload` are tracked, like the mtime backend it replaces.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

src/conf.c

@@ -25,8 +25,10 @@
 
 #include <dirent.h>
 #include <string.h>
+#include <sys/inotify.h>
 #include <sys/resource.h>
 #include <lite/lite.h>
+#include <lite/queue.h>		/* BSD sys/queue.h API */
 #include <sys/time.h>
 
 #include "finit.h"
@@ -40,8 +42,17 @@
 	(!strncasecmp(l, c, strlen(c)) && (x = (l) + strlen(c)))
 
 struct rlimit global_rlimit[RLIMIT_NLIMITS];
-static int parse_conf(char *file);
 
+struct conf_change {
+	TAILQ_ENTRY(conf_change) link;
+	char *name;
+};
+
+static uev_t w1, w2, w3;
+static TAILQ_HEAD(head, conf_change) conf_change_list = TAILQ_HEAD_INITIALIZER(conf_change_list);
+
+static int parse_conf(char *file);
+static void drop_changes(void);
 
 void conf_parse_cmdline(void)
 {
@@ -308,7 +319,7 @@ static void parse_static(char *line)
 	}
 }
 
-static void parse_dynamic(char *line, struct rlimit rlimit[], struct timeval *mtime)
+static void parse_dynamic(char *line, struct rlimit rlimit[], char *file)
 {
 	char *x;
 	char cmd[CMD_SIZE];
@@ -334,26 +345,26 @@ static void parse_dynamic(char *line, struct rlimit rlimit[], struct timeval *mt
 
 	/* Monitored daemon, will be respawned on exit */
 	if (MATCH_CMD(line, "service ", x)) {
-		service_register(SVC_TYPE_SERVICE, x, rlimit, mtime);
+		service_register(SVC_TYPE_SERVICE, x, rlimit, file);
 		return;
 	}
 
 	/* One-shot task, will not be respawned */
 	if (MATCH_CMD(line, "task ", x)) {
-		service_register(SVC_TYPE_TASK, x, rlimit, mtime);
+		service_register(SVC_TYPE_TASK, x, rlimit, file);
 		return;
 	}
 
 	/* Like task but waits for completion, useful w/ [S] */
 	if (MATCH_CMD(line, "run ", x)) {
-		service_register(SVC_TYPE_RUN, x, rlimit, mtime);
+		service_register(SVC_TYPE_RUN, x, rlimit, file);
 		return;
 	}
 
 	/* Classic inetd service */
 	if (MATCH_CMD(line, "inetd ", x)) {
 #ifdef INETD_ENABLED
-		service_register(SVC_TYPE_INETD, x, rlimit, mtime);
+		service_register(SVC_TYPE_INETD, x, rlimit, file);
 #else
 		_e("Finit built with inetd support disabled, cannot register service inetd %s!", x);
 #endif
@@ -368,7 +379,7 @@ static void parse_dynamic(char *line, struct rlimit rlimit[], struct timeval *mt
 
 	/* Regular or serial TTYs to run getty */
 	if (MATCH_CMD(line, "tty ", x)) {
-		tty_register(strip_line(x), rlimit, mtime);
+		tty_register(strip_line(x), rlimit, file);
 		return;
 	}
 }
@@ -384,7 +395,7 @@ static void tabstospaces(char *line)
 	}
 }
 
-static int parse_conf_dynamic(char *file, struct timeval *mtime)
+static int parse_conf_dynamic(char *file)
 {
 	FILE *fp;
 	struct rlimit rlimit[RLIMIT_NLIMITS];
@@ -409,7 +420,7 @@ static int parse_conf_dynamic(char *file, struct timeval *mtime)
 		tabstospaces(line);
 		_d("%s", line);
 
-		parse_dynamic(line, rlimit, mtime);
+		parse_dynamic(line, rlimit, file);
 	}
 
 	fclose(fp);
@@ -458,21 +469,26 @@ static int parse_conf(char *file)
 	return 0;
 }
 
-/* Reload all *.conf in /etc/finit.d/ */
-int conf_reload_dynamic(void)
+/*
+ * Reload /etc/finit.conf and all *.conf in /etc/finit.d/
+ */
+int conf_reload(void)
 {
 	int i, num;
-	char *dir = rcsd;
 	struct dirent **e;
 
 	/* Mark and sweep */
 	svc_mark_dynamic();
 	tty_mark();
 
-	num = scandir(dir, &e, NULL, alphasort);
+	/* First, read /etc/finit.conf */
+	parse_conf(FINIT_CONF);
+
+	/* Next, read all *.conf in /etc/finit.d/ */
+	num = scandir(rcsd, &e, NULL, alphasort);
 	if (num < 0) {
-		_d("Skipping %s, no files found ...", dir);
-		return 1;
+		_d("Skipping %s, no files found ...", rcsd);
+		return 0;
 	}
 
 	/* Update global limits in case operator used prlimit(1) on us */
@@ -484,13 +500,11 @@ int conf_reload_dynamic(void)
 		char  path[LINE_SIZE];
 		size_t len;
 		struct stat st;
-		struct timeval mtime;
 
-		snprintf(path, sizeof(path), "%s/%s", dir, name);
+		snprintf(path, sizeof(path), "%s/%s", rcsd, name);
 
 		/* Check that it's an actual file ... beyond any symlinks */
 		if (lstat(path, &st)) {
-		lost:
 			_d("Skipping %s, cannot access: %s", path, strerror(errno));
 			continue;
 		}
@@ -521,27 +535,210 @@ int conf_reload_dynamic(void)
 			continue;
 		}
 
-		if (stat(path, &st))
-			goto lost; /* Weird, lost file between here and lstat() */
-
-		TIMESPEC_TO_TIMEVAL(&mtime, &st.st_mtim);
-		parse_conf_dynamic(path, &mtime);
+		parse_conf_dynamic(path);
 	}
 
 	while (num--)
 		free(e[num]);
 	free(e);
 
+	/* Drop record of all .conf changes */
+	drop_changes();
+
+	/*
+	 * Set host name, from %DEFHOST, *.conf or /etc/hostname.  The
+	 * latter wins, if neither exists we default to "noname"
+	 */
 	set_hostname(&hostname);
 
 	return 0;
 }
 
-int conf_parse_config(void)
+static struct conf_change *conf_find(char *file)
+{
+	struct conf_change *node, *tmp;
+
+	TAILQ_FOREACH_SAFE(node, &conf_change_list, link, tmp) {
+		if (string_compare(node->name, file))
+			return node;
+	}
+
+	return NULL;
+}
+
+static void drop_change(struct conf_change *node)
+{
+	if (!node)
+		return;
+
+	TAILQ_REMOVE(&conf_change_list, node, link);
+	free(node->name);
+	free(node);
+}
+
+
+static void drop_changes(void)
+{
+	struct conf_change *node, *tmp;
+
+	TAILQ_FOREACH_SAFE(node, &conf_change_list, link, tmp)
+		drop_change(node);
+}
+
+static int do_change(char *name, uint32_t mask)
+{
+	struct conf_change *node;
+
+	node = conf_find(name);
+	if (mask & (IN_DELETE | IN_MOVED_FROM)) {
+		drop_change(node);
+		return 0;
+	}
+
+	if (node) {
+		_d("Event already registered for %s ...", name);
+		return 0;
+	}
+
+	node = malloc(sizeof(*node));
+	if (!node)
+		return 1;
+
+	node->name = strdup(name);
+	if (!node->name) {
+		free(node);
+		return 1;
+	}
+
+	TAILQ_INSERT_HEAD(&conf_change_list, node,link);
+
+	return 0;
+}
+
+int conf_changed(char *file)
+{
+	char *ptr;
+
+	if (file && (ptr = strrchr(file, '/')))
+		file = ++ptr;
+
+	if (conf_find(file))
+		return 1;
+
+	return 0;
+}
+
+static void conf_cb(uev_t *w, void *arg, int events)
+{
+	static char ev_buf[8 *(sizeof(struct inotify_event) + NAME_MAX + 1) + 1];
+	struct inotify_event *ev;
+	ssize_t sz, len;
+
+	sz = read(w->fd, ev_buf, sizeof(ev_buf) - 1);
+	if (sz <= 0) {
+		_pe("invalid inotify event");
+		return;
+	}
+	ev_buf[sz] = 0;
+	ev = (struct inotify_event *)ev_buf;
+
+	if (arg) {
+		do_change(arg, ev->mask);
+		return;
+	}
+
+	for (ev = (void *)ev_buf; sz > (ssize_t)sizeof(*ev);
+	     len = sizeof(*ev) + ev->len, ev = (void *)ev + len, sz -= len) {
+		if (do_change(ev->name, ev->mask)) {
+			_pe("conf_monitor: Out of memory");
+			break;
+		}
+	}
+}
+
+static int add_watcher(uev_ctx_t *ctx, uev_t *w, char *path, uint32_t opt)
+{
+	struct stat st;
+	uint32_t mask = IN_CREATE | IN_DELETE | IN_MODIFY | IN_ATTRIB | IN_MOVE;
+	char *arg = NULL;
+	int fd, wd;
+
+	if (!ctx)
+		return 0;
+
+	if (stat(path, &st)) {
+		_d("No such file or directory, skipping %s", path);
+		w->fd = -1;
+		return 0;
+	}
+	if (!S_ISDIR(st.st_mode)) {
+		arg = strrchr(path, '/');
+		if (!arg)
+			arg = path;
+		else
+			arg++;
+	}
+
+	if (w->fd >= 0)
+		close(w->fd);
+
+	fd = inotify_init1(IN_NONBLOCK | IN_CLOEXEC);
+	if (fd < 0) {
+		_pe("Failed creating inotify descriptor");
+		w->fd = -1;
+		return 1;
+	}
+
+	/*
+	 * Only forward error, don't report error,
+	 * user may not have @path and that's OK
+	 */
+	wd = inotify_add_watch(fd, path, mask | opt);
+	if (wd < 0) {
+		w->fd = -1;
+		close(fd);
+		return 1;
+	}
+
+	if (uev_io_init(ctx, w, conf_cb, arg, fd, UEV_READ)) {
+		_pe("Failed setting up I/O callback for %s watcher", path);
+		w->fd = -1;
+		close(fd);
+		return 1;
+	}
+
+	return 0;
+}
+
+/*
+ * Set up inotify watcher and load all *.conf in /etc/finit.d/
+ */
+int conf_monitor(uev_ctx_t *ctx)
+{
+	int rc = 0;
+
+	/*
+	 * If only one watcher fails, that's OK.  A user may have only
+	 * one of /etc/finit.conf or /etc/finit.d in use, and may also
+	 * have or not have symlinks in place.  We need to monitor for
+	 * changes to either symlink or target.
+	 */
+	rc += add_watcher(ctx, &w1, FINIT_RCSD, 0);
+	rc += add_watcher(ctx, &w2, FINIT_RCSD "/available", IN_DONT_FOLLOW);
+	rc += add_watcher(ctx, &w3, FINIT_CONF, 0);
+
+	return rc + conf_reload();
+}
+
+/*
+ * Prepare .conf parser and load all .conf files
+ */
+int conf_init(void)
 {
 	hostname = strdup(DEFHOST);
+	w1.fd = w2.fd = w3.fd = -1;
 
-	return parse_conf(FINIT_CONF) || conf_reload_dynamic();
+	return conf_monitor(NULL);
 }
 
 /**