Add housekeeping functions to clean up unused cgroups

This should not be needed, but for some reason we don't get events when
early processes exit, so we end up with lingering cgroups.

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

src/cgroup.c

@@ -21,6 +21,7 @@
  * THE SOFTWARE.
  */
 
+#include <dirent.h>
 #include <errno.h>
 #include <stdio.h>
 #include <string.h>
@@ -673,6 +674,79 @@ int cgroup_add(char *name, char *cfg, int is_protected)
 	return 0;
 }
 
+/*
+ * Walk a cgroup directory and remove all empty subdirectories recursively.
+ */
+static void cgroup_prune_recursive(const char *path)
+{
+	struct dirent *d;
+	DIR *dir;
+
+	dir = opendir(path);
+	if (!dir)
+		return;
+
+	while ((d = readdir(dir)) != NULL) {
+		char subpath[PATH_MAX];
+
+		if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
+			continue;
+		if (d->d_type != DT_DIR)
+			continue;
+
+		snprintf(subpath, sizeof(subpath), "%s/%s", path, d->d_name);
+		cgroup_prune_recursive(subpath);
+	}
+	closedir(dir);
+
+	/*
+	 * Try to remove this directory. If it still has children or processes,
+	 * rmdir() will fail with ENOTEMPTY/EBUSY - that's fine.
+	 */
+	if (rmdir(path) && errno != ENOTEMPTY && errno != EBUSY)
+		warn("Failed to prune %s", path);
+}
+
+/*
+ * Housekeeping: prune all empty cgroup subdirectories.
+ * Called after runlevel transitions to clean up finished run/task cgroups.
+ */
+void cgroup_prune(void)
+{
+	struct dirent *entry;
+	struct cg *cg;
+	char path[256];
+	DIR *dir;
+
+	if (!avail)
+		return;
+
+	dbg("Pruning empty cgroup directories...");
+
+	/* Walk through each top-level cgroup (init, system, user) */
+	TAILQ_FOREACH(cg, &cgroups, link) {
+		snprintf(path, sizeof(path), FINIT_CGPATH "/%s", cg->name);
+
+		dir = opendir(path);
+		if (!dir)
+			continue;
+
+		/* Check each subdirectory */
+		while ((entry = readdir(dir)) != NULL) {
+			char subpath[512];
+
+			if (!strcmp(entry->d_name, ".") || !strcmp(entry->d_name, ".."))
+				continue;
+			if (entry->d_type != DT_DIR)
+				continue;
+
+			snprintf(subpath, sizeof(subpath), "%s/%s", path, entry->d_name);
+			cgroup_prune_recursive(subpath);
+		}
+		closedir(dir);
+	}
+}
+
 /*
  * Remove inactive top-level cgroup
  */
@@ -696,7 +770,8 @@ int cgroup_del(char *dir)
 	}
 
 	if (rmdir(dir) && errno != ENOENT) {
-		dbg("Failed removing %s: %s", dir, strerror(errno));
+		if (errno != EBUSY)
+			warn("Failed rmdir(%s): %s", dir, strerror(errno));
 		return -1;
 	}