conf: add provides, additional conditions a service supplies

A block title is a service identity, so two variants of one service
gated differently per platform cannot share a title.  They do need to
share the barrier condition downstream services wait for, which until
now was spelled by the identity alone and so could not be shared:

    service syslogd:udev {
        if         = "udevd"
        conditions = { "run/udevadm:5/success" }
        provides   = "pid/syslogd"
        command    = "-syslogd -F"
    }

Any namespace is allowed, since the point is publishing a name that
existing configurations already wait on.  A claim on a condition that
is already owned is dropped with a warning naming the owner, and the
service still registers: the overlap is a configuration bug, and an
init system is more useful degraded than refusing to boot.  A real
identity outranks a claim, pid/<ident> is how Finit tracks its own
services, so it is not up for grabs.

Claims are dropped before each reload re-reads the .conf files.  Doing
it per service as it re-registers is not enough, since services are
read in file order and one re-registering would lose to a claim
another had not dropped yet, flipping the owner on every reload.

initctl cond dump asked who owned a condition only for the pid/
namespace and printed 'static' for usr/, which now hides a provider.
It asks first and falls back to what the namespace implies.

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

src/conf.c

@@ -288,6 +288,7 @@ static cfg_opt_t svc_opts[] = {
 	CFG_INT     ("config-dir-mode",      0, CFGF_NODEFAULT),
 	CFG_STR     ("runtime-dir-preserve", NULL, CFGF_NODEFAULT),
 	CFG_STR_LIST("conflicts",    NULL, CFGF_NODEFAULT),
+	CFG_STR_LIST("provides",     NULL, CFGF_NODEFAULT),
 	CFG_STR     ("if",           NULL, CFGF_NODEFAULT),
 	CFG_STR     ("tty",          NULL, CFGF_NODEFAULT),
 	/*
@@ -1382,6 +1383,58 @@ static int if_translate(const char *str, char *buf, size_t len, char *file, cons
 	return 0;
 }
 
+/*
+ * provides names conditions this service asserts on top of its own
+ * pid/<ident>, so blocks with distinct titles can supply one barrier
+ * to everything downstream.  Like the per-service directories it has
+ * no legacy token and is stored on the registered svc.
+ *
+ * A claim on a condition that is already owned is dropped, with the
+ * service itself left alone: the overlap is a configuration bug, and
+ * an init system is more useful degraded than refusing to boot.
+ */
+static void provides_translate(cfg_t *sec, svc_t *svc, char *file)
+{
+	unsigned int i, num;
+
+	num = cfg_size(sec, "provides");
+	for (i = 0; i < num; i++) {
+		const char *cond = cfg_getnstr(sec, "provides", i);
+		svc_t *owner;
+
+		if (!strchr(cond, '/')) {
+			logit(LOG_ERR, "%s: %s: provides '%s' is not a condition,"
+			      " it needs a namespace, e.g. usr/%s, ignoring",
+			      file, cfg_title(sec), cond, cond);
+			continue;
+		}
+
+		if (strlen(cond) >= MAX_COND_LEN) {
+			logit(LOG_ERR, "%s: %s: provides '%s' is too long,"
+			      " ignoring", file, cfg_title(sec), cond);
+			continue;
+		}
+
+		if (svc->num_provides >= MAX_NUM_PROVIDES) {
+			logit(LOG_WARNING, "%s: %s: too many provides, max %d,"
+			      " ignoring '%s'", file, cfg_title(sec),
+			      MAX_NUM_PROVIDES, cond);
+			break;
+		}
+
+		owner = svc_cond_owner(cond, svc);
+		if (owner) {
+			logit(LOG_WARNING, "%s: %s: provides condition <%s>"
+			      " already registered by service %s, ignoring",
+			      file, cfg_title(sec), cond,
+			      svc_ident(owner, NULL, 0));
+			continue;
+		}
+
+		strlcpy(svc->provides[svc->num_provides++], cond, MAX_COND_LEN);
+	}
+}
+
 /*
  * These have no legacy token, they are validated by service_set_dir()
  * and stored directly on the registered svc.  Empty means unset,
@@ -1644,6 +1697,7 @@ static void svc_translate(cfg_t *sec, int type, struct rlimit rlimit[], char *fi
 		return;
 
 	dirs_translate(sec, svc, file);
+	provides_translate(sec, svc, file);
 }
 
 /*
@@ -2199,6 +2253,7 @@ int conf_reload(void)
 	cgroup_mark_all();
 	svc_mark_dynamic();
 	conf_reset_env();
+	svc_provides_reset();
 
 	/*
 	 * Reset global rlimit to bootstrap values from conf_init().

src/initctl.c

@@ -337,6 +337,7 @@ static int dump_one_cond(const char *fpath, const struct stat *sb, int tflag, st
 	const char *cond, *asserted;
 	char *nm = "init";
 	pid_t pid = 1;
+	svc_t *svc;
 
 	if (tflag != FTW_F)
 		return 0;
@@ -350,17 +351,18 @@ static int dump_one_cond(const char *fpath, const struct stat *sb, int tflag, st
 	if (dump_filter && dump_filter[0] && strncmp(cond, dump_filter, strlen(dump_filter)))
 		return 0;
 
-	if (strncmp("pid/", cond, 4) == 0) {
-		svc_t *svc;
-
-		svc = client_svc_find_by_cond(cond);
-		if (!svc) {
-			nm  = "unknown";
-			pid = 0;
-		} else {
-			nm  = svc_ident(svc, NULL, 0);
-			pid = svc->pid;
-		}
+	/*
+	 * Any namespace can be claimed with provides, so ask who owns
+	 * the condition before falling back to what the namespace
+	 * implies on its own.
+	 */
+	svc = client_svc_find_by_cond(cond);
+	if (svc) {
+		nm  = svc_ident(svc, NULL, 0);
+		pid = svc->pid;
+	} else if (strncmp("pid/", cond, 4) == 0) {
+		nm  = "unknown";
+		pid = 0;
 	} else if (strncmp("usr/", cond, 4) == 0) {
 		nm  = "static";
 		pid = 0;

src/service.c

@@ -2391,6 +2391,7 @@ svc_t *service_register(int type, char *cfg, struct rlimit rlimit[], char *file)
 		svc->dir_mode[i] = 0755;
 	}
 	svc->dir_preserve = SVC_DIR_PRESERVE_NO;
+	svc->num_provides = 0;
 
 	if (!svc_is_tty(svc) && ctty) {
 		char *dev = ctty;