librc: Add initial support for dynamically multiplexed services.origin/dynamic-multiplex

Generate a new directory on the service dir, "multiplexed", which will
hold all the symlinks we generate at runtime, and a new librc function,
"rc_service_multiplex", which takes a basename or service path, and a
variant name, then generated a symlink to the base service from the
multiplex dir.

This allows multiplexing services at runtime, possibly using data
acquired at runtime, such as the name of an user or interface.

3 files changed, 52 insertions, 2 deletions

diff --git a/src/librc/librc-depend.c b/src/librc/librc-depend.c
index a48a2ada..8f569ae5 100644
--- a/src/librc/librc-depend.c
+++ b/src/librc/librc-depend.c
@@ -697,6 +697,7 @@ static const char *const depdirs[] =
 	RC_SVCDIR "/wasinactive",
 	RC_SVCDIR "/failed",
 	RC_SVCDIR "/hotplugged",
+	RC_SVCDIR "/multiplexed",
 	RC_SVCDIR "/daemons",
 	RC_SVCDIR "/options",
 	RC_SVCDIR "/exclusive",
diff --git a/src/librc/librc.c b/src/librc/librc.c
index b5449641..0d114214 100644
--- a/src/librc/librc.c
+++ b/src/librc/librc.c
@@ -636,6 +636,12 @@ rc_service_resolve(const char *service)
 		return file;
 #endif
 
+	/* Check dynamically multiplexed services last */
+	free(file);
+	xasprintf(&file, "%s/multiplexed/%s", RC_SVCDIR, service);
+	if (stat(file, &buf) == 0)
+		return file;
+
 	free(file);
 	return NULL;
 }
@@ -934,6 +940,32 @@ rc_service_state(const char *service)
 }
 
 char *
+rc_service_multiplex(const char *base, const char *variant)
+{
+	char *service = rc_service_resolve(base);
+	char *target;
+	char *name;
+
+	if (!service)
+		return NULL;
+
+	if (base[0] == '/')
+		base = basename_c(base);
+
+	xasprintf(&name, "%s.%s", base, variant);
+
+	xasprintf(&target, "%s/multiplexed/%s", RC_SVCDIR, name);
+	if (!exists(target) && symlink(service, target) == -1) {
+		free(target);
+		target = NULL;
+	}
+
+	free(name);
+	free(service);
+	return target;
+}
+
+char *
 rc_service_value_get(const char *service, const char *option)
 {
 	char *buffer = NULL;
@@ -1119,6 +1151,8 @@ rc_service_add(const char *runlevel, const char *service)
 	char *path;
 	char *binit = NULL;
 	char *i;
+	char *multiplex_dir;
+	int len;
 
 	if (!rc_runlevel_exists(runlevel)) {
 		errno = ENOENT;
@@ -1151,10 +1185,20 @@ rc_service_add(const char *runlevel, const char *service)
 		i = binit;
 	}
 
-	xasprintf(&file, "%s/%s/%s", RC_RUNLEVELDIR, runlevel,
-		basename_c(service));
+	/* We shouldn't add any dynamically multiplexed service to a runlevel */
+	len = xasprintf(&multiplex_dir, "%s/multiplexed", RC_SVCDIR);
+	if (strncmp(i, multiplex_dir, len) == 0) {
+		errno = ENOENT;
+		retval = false;
+		goto out;
+	}
+
+	xasprintf(&file, "%s/%s/%s", RC_RUNLEVELDIR, runlevel, basename_c(service));
 	retval = (symlink(i, file) == 0);
 	free(file);
+
+out:
+	free(multiplex_dir);
 	free(binit);
 	free(init);
 	return retval;
diff --git a/src/librc/rc.h.in b/src/librc/rc.h.in
index d90943b6..4fdd3ef3 100644
--- a/src/librc/rc.h.in
+++ b/src/librc/rc.h.in
@@ -267,6 +267,11 @@ bool rc_service_schedule_clear(const char *);
  * @return state of the service */
 RC_SERVICE rc_service_state(const char *);
 
+/*! Dynamically multiplexes a base service into a variant as basename.variant
+ * @param basename or full path of service being multiplexed
+ * @param variant to dynamically multiplex */
+char *rc_service_multiplex(const char *, const char *);
+
 /*! Check if the service started the daemon
  * @param service to check
  * @param exec to check