Initial support for templating and instantiating services

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

README.md

@@ -41,6 +41,7 @@ Features include:
     startup, support for systemd [sd_notify()][], or [s6 style][] too
   * Limited support for [tmpfiles.d(5)][] (no aging, attributes, or subvolumes)
   * Pre/Post script actions
+  * Rudimentary [templating support](doc/config.md#templating)
   * Tooling to enable/disable services
   * Built-in getty
   * Built-in watchdog, with support for hand-over to [watchdogd](https://troglobit.com/watchdogd.html)

doc/config.md

@@ -9,6 +9,7 @@ Finit Configuration
 * [Service Environment](#service-environment)
 * [Service Synchronization](#service-synchronization)
 * [Service Wrapper Scripts](#service-wrapper-scripts)
+* [Templating](#templating)
 * [Cgroups](#cgroups)
 * [Configuration File Syntax](#configuration-file-syntax)
   * [Hostname](#hostname)
@@ -353,6 +354,26 @@ example employs a wrapper script in `/etc/start.d`.
 >           instead of sending SIGHUP at restart/reload events.
 
 
+Templating
+----------
+
+Finit comes with rudimentary support for templating, similar to that of
+systemd.  Best illustrated with an example:
+
+      $ initctl show avahi-autoipd@
+      service :%i avahi-autoipd --syslog %i -- ZeroConf for %i
+
+To enable ZeroConf for, e.g., eth0, use
+
+      $ initctl enable avahi-autoipd@eth0.conf
+
+The enabled symlink will be set up to avahi-autoipd@.conf and every in‐
+stance of %i will in the instantiated directive be replaced with eth0.
+Inspect the result with:
+
+      $ initctl status avahi-autoipd:eth0
+
+
 Cgroups
 -------
 

man/finit.conf.5

@@ -2,7 +2,7 @@
 .\" First parameter, NAME, should be all caps
 .\" Second parameter, SECTION, should be 1-8, maybe w/ subsection
 .\" other parameters are allowed: see man(7), man(1)
-.Dd Apr 22, 2023
+.Dd Apr 24, 2023
 .Dt FINIT.CONF 5 SMM
 .Os Linux
 .Sh NAME
@@ -325,9 +325,10 @@ service notify:s6 mdevd -C -O 4 -D %n
 When a service is ready, either by Finit detecting its PID file, or
 their respective readiness mechanism has been triggered, Finit creates
 then service's ready condition which other services can depend on:
-
-    $ initctl -v cond get service/mdevd/ready
-    on
+.Bd -unfilled -offset indent
+$ initctl -v cond get service/mdevd/ready
+on
+.Ed
 .El
 .Pp
 If a service should not be automatically started, it can be configured
@@ -818,6 +819,31 @@ the example sets
 to denote that it doesn't support SIGHUP.  That way Finit will
 stop/start the service instead of sending SIGHUP at restart/reload
 events.
+.Sh TEMPLATING
+Finit comes with rudimentary support for templating, similar to that of
+systemd.  Best illustrated with an example:
+.Bd -unfilled -offset indent
+$ initctl show avahi-autoipd@
+service :%i avahi-autoipd --syslog %i -- ZeroConf for %i
+.Ed
+.Pp
+To enable ZeroConf for, e.g.,
+.Cm eth0 ,
+use
+.Bd -unfilled -offset indent
+$ initctl enable avahi-autoipd@eth0.conf
+.Ed
+.Pp
+The enabled symlink will be set up to
+.Cm avahi-autoipd@.conf
+and every instance of
+.Cm %i
+will in the instantiated directive be replaced with
+.Cm eth0 .
+Inspect the result with:
+.Bd -unfilled -offset indent
+$ initctl status avahi-autoipd:eth0
+.Ed
 .Sh CGROUPS
 There are three major cgroup configuration directives:
 .Pp

src/conf.c

@@ -914,11 +914,79 @@ static int parse_dynamic(char *line, struct rlimit rlimit[], char *file)
 	return 1;
 }
 
+/*
+ * Very simple and crude implementation, only supports '%i'
+ */
+static char *instantiate(char *line, char *name)
+{
+	char *ptr, *end = strchr(line, 0);
+	char *pos = line;
+	size_t num = 0;
+
+	if (!name[0] || !end)
+		return line;
+
+	while ((ptr = strchr(pos, '%'))) {
+		num++;
+		pos++;
+	}
+
+	ptr = realloc(line, strlen(line) + num * strlen(name) + 1);
+	if (!ptr)
+		return line;
+
+	pos = line = ptr;
+	while ((ptr = strchr(pos, '%'))) {
+		if (!strncmp(ptr, "%i", 2)) {
+			char *rest = &ptr[2];
+			char *next = ptr + strlen(name);
+
+			memmove(next, rest, strlen(rest) + 1);
+			memcpy(ptr, name, strlen(name));
+
+			pos += strlen(name);
+		} else
+			pos++;
+	}
+
+	return line;
+}
+
+static int is_template(const char *file, char *name, size_t len)
+{
+	char *ptr, *nm;
+	size_t i = 0;
+
+	ptr = strchr(file, '@');
+	if (!ptr)
+		return 0;	/* not a template */
+
+	nm = ptr + 1;
+	ptr = strstr(nm, ".conf");
+	if (!strcmp(nm, ".conf") || !ptr)
+		return 1;	/* template itself or invalid */
+
+	while (nm < ptr && i < len - 1)
+		name[i++] = *nm++;
+	name[i] = 0;
+
+	return 1;		/* instantiated template */
+}
+
 static int parse_conf(char *file, int is_rcsd)
 {
 	struct rlimit rlimit[RLIMIT_NLIMITS];
+	char name[65] = { 0 };
 	FILE *fp;
 
+	if (is_template(file, name, sizeof(name))) {
+		if (!name[0]) {
+			dbg("*** Skipping template file %s", file);
+			return 0;
+		}
+		dbg("*** instantiating %s from %s ...", name, file);
+	}
+
 	fp = fopen(file, "r");
 	if (!fp)
 		return 1;
@@ -938,7 +1006,9 @@ static int parse_conf(char *file, int is_rcsd)
 			continue;
 
 		tabstospaces(line);
-//		dbg("%s", line);
+//		dbg("raw: %s", line);
+		line = instantiate(line, name);
+//		dbg("ins: %s", line);
 
 		if (!parse_static(line, is_rcsd))
 			;

src/serv.c

@@ -253,18 +253,18 @@ static char *conf(char *path, size_t len, char *name, int creat)
 
 int serv_enable(char *arg)
 {
+	char src[strlen(arg) + 6];
 	size_t arglen, len;
-	char corr[40];
+	char *ptr;
 
 	if (!arg || !arg[0]) {
 		WARNX("missing argument to enable, may be one of:");
 		return serv_list("available");
 	}
 
-	if (!strstr(arg, ".conf")) {
-		snprintf(corr, sizeof(corr), "%s.conf", arg);
-		arg = corr;
-	}
+	strlcpy(src, arg, sizeof(src));
+	if (!strstr(src, ".conf"))
+		strlcat(src, ".conf", sizeof(src));
 
 	if (chdir(finit_rcsd))
 		ERR(72, "failed cd %s", finit_rcsd);
@@ -272,13 +272,21 @@ int serv_enable(char *arg)
 	if (icreate && mkdir("enabled", 0755) && EEXIST != errno)
 		ERR(73, "failed creating %s/enabled directory", finit_rcsd);
 
-	len    = snprintf(NULL, 0, "%s/available/%s", finit_rcsd, arg);
+	len    = snprintf(NULL, 0, "%s/available/%s", finit_rcsd, src);
 	arglen = snprintf(NULL, 0, "%s/enabled/%s", finit_rcsd, arg);
 	char argpath[arglen + 1], path[len + 1];
 
-	snprintf(path, sizeof(path), "%s/available/%s", finit_rcsd, arg);
+	snprintf(path, sizeof(path), "%s/available/%s", finit_rcsd, src);
+
+	/* check for template instatiation */
+	ptr = strchr(path, '@');
+	if (ptr++) {
+		*ptr = 0;
+		strlcat(path, ".conf", sizeof(path));
+	}
+
 	if (!fexist(path))
-		ERRX(72, "cannot find %s", path);
+		ERRX(72, "cannot find %s%s", ptr ? "template ": "", path);
 
 	snprintf(argpath, sizeof(argpath), "%s/enabled/%s", finit_rcsd, arg);
 	if (fexist(argpath))