Refactor, clean up removed top-level cgroups

The main purpose of this patch is to remove top-level cgroups when they
are remvoed from finit.conf.  However, this is tricky, becasue there may
still be supervised services (and children of them) running.  We must
postpone removal until a cgroup.events change.  To make matters worse,
events may arrive out-of-order, i.e. the last-child event for the parent
cgroup before the sub-group.

A spin-off from this patch is that we can now support arbitrarily long
group names and group config.  (Only applies to top-level cgroups, not
run/task/services.)

Limitations:
 - Processes in "removed" cgroups are not migrated/orphaned, the reasons
   are several: overhead and complexity and the fact that memory cannot
   be migrated
 - A lingering child of a moved service may prevent an old top-level
   cgroup from being removed.

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

src/cgroup.c

@@ -25,6 +25,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <lite/lite.h>
+#include <lite/queue.h>
 #include <sys/mount.h>
 #include <sys/sysinfo.h>		/* get_nprocs_conf() */
 
@@ -34,6 +35,18 @@
 #include "log.h"
 #include "util.h"
 
+struct cg {
+	TAILQ_ENTRY(cg) link;
+
+	char *name;		/* top-level group name */
+	char *cfg;		/* kernel settings */
+
+	int  active;		/* for mark & sweep */
+	int  protected;		/* for init/, user/, & system/ */
+};
+
+static TAILQ_HEAD(, cg) cgroups = TAILQ_HEAD_INITIALIZER(cgroups);
+
 static char controllers[256];
 
 static struct iwatch iw_cgroup;
@@ -205,7 +218,17 @@ static void cgroup_handle_event(char *event, uint32_t mask)
 		ptr = strrchr(path, '/');
 		if (ptr) {
 			*ptr = 0;
-			rmdir(path);
+			if (!cgroup_del(path)) {
+				/*
+				 * try with parent, top-level group, we
+				 * may get events out-of-order *sigh*
+				 */
+				ptr = strrchr(path, '/');
+				if (!ptr)
+					break;
+				*ptr = 0;
+				cgroup_del(path);
+			}
 		}
 
 		break;
@@ -255,6 +278,151 @@ static void cgroup_events_cb(uev_t *w, void *arg, int events)
 #endif
 }
 
+static struct cg *cgroup_find(char *name)
+{
+	struct cg *cg;
+
+	TAILQ_FOREACH(cg, &cgroups, link) {
+		if (strcmp(cg->name, name))
+			continue;
+
+		return cg;
+	}
+
+	return NULL;
+}
+
+/*
+ * Marks all unprotected cgroups for deletion (during reload)
+ */
+void cgroup_mark_all(void)
+{
+	struct cg *cg;
+
+	TAILQ_FOREACH(cg, &cgroups, link) {
+		if (cg->protected)
+			continue;
+
+		cg->active = 0;
+	}
+}
+
+/*
+ * Remove (try to) all unused cgroups
+ */
+void cgroup_cleanup(void)
+{
+	struct cg *cg, *tmp;
+	char path[256];
+
+	TAILQ_FOREACH_SAFE(cg, &cgroups, link, tmp) {
+		if (cg->active)
+			continue;
+
+		snprintf(path, sizeof(path), FINIT_CGPATH "/%s", cg->name);
+		cgroup_del(path);
+	}
+}
+
+/*
+ * Add, or update, settings for top-level cgroup
+ */
+int cgroup_add(char *name, char *cfg, int protected)
+{
+	struct cg *cg;
+
+	if (!name)
+		return -1;
+	if (!cfg)
+		cfg = "";
+
+	cg = cgroup_find(name);
+	if (!cg) {
+		cg = malloc(sizeof(struct cg));
+		if (!cg) {
+			_pe("Failed allocating 'struct cg' for %s", name);
+			return -1;
+		}
+		cg->name = strdup(name);
+		if (!cg->name) {
+			_pe("Failed setting cgroup name %s", name);
+			free(cg);
+			return -1;
+		}
+		TAILQ_INSERT_TAIL(&cgroups, cg, link);
+	} else
+		free(cg->cfg);
+
+	cg->cfg = strdup(cfg);
+	if (!cg->cfg) {
+		_pe("Failed add/update of cgroup %s", name);
+		TAILQ_REMOVE(&cgroups, cg, link);
+		free(cg->name);
+		free(cg);
+		return -1;
+	}
+	cg->protected = protected;
+	cg->active = 1;
+
+	return 0;
+}
+
+/*
+ * Remove inactive top-level cgroup
+ */
+int cgroup_del(char *dir)
+{
+	struct cg *cg;
+	char path[256];
+
+	TAILQ_FOREACH(cg, &cgroups, link) {
+		snprintf(path, sizeof(path), FINIT_CGPATH "/%s", cg->name);
+		if (strcmp(path, dir))
+			continue;
+
+		if (cg->active)
+			return -1;
+
+		break;
+	}
+
+	if (rmdir(dir) && errno != ENOENT) {
+		_d("Failed removing %s: %s", dir, strerror(errno));
+		return -1;
+	}
+
+	if (cg) {
+		TAILQ_REMOVE(&cgroups, cg, link);
+		free(cg->name);
+		free(cg->cfg);
+		free(cg);
+	}
+
+	return 0;
+}
+
+/* the top-level init cgroup is a leaf, that's ensured in cgroup_init() */
+void cgroup_config(void)
+{
+	struct cg *cg;
+
+	TAILQ_FOREACH(cg, &cgroups, link) {
+		char path[256];
+		int leaf = 0;
+
+		if (!cg->active)
+			continue;
+		if (!strcmp(cg->name, "init"))
+			leaf = 1;	/* reserved */
+
+		snprintf(path, sizeof(path), "%s/%s", FINIT_CGPATH, cg->name);
+		group_init(path, leaf, cg->cfg);
+
+		strlcat(path, "/cgroup.events", sizeof(path));
+		iwatch_add(&iw_cgroup, path, 0);
+	}
+}
+
 /*
  * Called by Finit at early boot to mount initial cgroups
  */
@@ -293,10 +461,11 @@ void cgroup_init(uev_ctx_t *ctx)
 	if (fnwrite(controllers, FINIT_CGPATH "/cgroup.subtree_control"))
 		_pe("Failed enabling %s for %s", controllers, FINIT_CGPATH "/cgroup.subtree_control");
 
-	/* Default groups, PID 1, services, and user/login processes */
-	group_init(FINIT_CGPATH "/init",   1, "cpu.weight:100");
-	group_init(FINIT_CGPATH "/user",   0, "cpu.weight:100");
-	group_init(FINIT_CGPATH "/system", 0, "cpu.weight:9800");
+	/* Default (protected) groups, PID 1, services, and user/login processes */
+	cgroup_add("init",   "cpu.weight:100",  1);
+	cgroup_add("system", "cpu.weight:9800", 1);
+	cgroup_add("user",   "cpu.weight:100",  1);
+	cgroup_config();
 
 	/* Move ourselves to init (best effort, otherwise run in 'root' group */
 	if (fnwrite("1", FINIT_CGPATH "/init/cgroup.procs"))
@@ -310,23 +479,6 @@ void cgroup_init(uev_ctx_t *ctx)
 	}
 }
 
-/* the top-level init cgroup is a leaf, that's ensured in cgroup_init() */
-void cgroup_config(size_t num, struct cgroup cg[])
-{
-	size_t i;
-
-	for (i = 0; i < num; i++) {
-		char path[256];
-		int leaf = 0;
-
-		if (!strcmp(cg[i].name, "init"))
-		    leaf = 1;		/* reserved */
-
-		snprintf(path, sizeof(path), "%s/%s", FINIT_CGPATH, cg[i].name);
-		group_init(path, leaf, cg[i].cfg);
-	}
-}
-
 /**
  * Local Variables:
  *  indent-tabs-mode: t

src/cgroup.h

@@ -31,8 +31,14 @@ struct cgroup {
 	char cfg[128];
 };
 
+void cgroup_mark_all(void);
+void cgroup_cleanup (void);
+
+int  cgroup_add     (char *name, char *cfg, int protected);
+int  cgroup_del     (char *dir);
+void cgroup_config  (void);
+
 void cgroup_init    (uev_ctx_t *ctx);
-void cgroup_config  (size_t num, struct cgroup cg[]);
 
 int  cgroup_user    (char *name, int pid);
 int  cgroup_service (char *name, int pid, struct cgroup *cg);

src/conf.c

@@ -51,8 +51,6 @@ int logfile_count_max = 5;
 struct rlimit initial_rlimit[RLIMIT_NLIMITS];
 struct rlimit global_rlimit[RLIMIT_NLIMITS];
 
-struct cgroup cgroups[8];
-size_t cgroups_num;
 char cgroup_current[16]; /* cgroup.NAME sets current cgroup for a set of services */
 
 struct conf_change {
@@ -428,65 +426,27 @@ error:
 	logit(LOG_WARNING, "rlimit: parse error");
 }
 
-/* reset defaults */
-static void init_cgroups(void)
-{
-	struct cgroup init[3] = {
-		{ .name = "init",   .cfg = "cpu.weight:100"  },
-		{ .name = "user",   .cfg = "cpu.weight:100"  },
-		{ .name = "system", .cfg = "cpu.weight:9800" },
-	};
-	size_t i;
-
-	for (i = 0; i < NELEMS(init); i++)
-		memcpy(&cgroups[i], &init[i], sizeof(struct cgroup));
-
-	cgroups_num = i;
-}
-
-struct cgroup *conf_cgfind(char *name)
-{
-	size_t i;
-
-	for (i = 0; i < cgroups_num; i++) {
-		if (strcmp(cgroups[i].name, name))
-			continue;
-
-		return &cgroups[i];
-	}
-
-	return NULL;
-}
-
 /* cgroup NAME ctrl.prop:value,ctrl.prop:value ... */
 static void conf_parse_cgroup(char *line)
 {
-	struct cgroup *cg;
+	char config[strlen(line)];
 	char *ptr, *name;
 
 	name = strtok(line, " \t");
 	if (!name)
 		return;
 
-	cg = conf_cgfind(name);
-	if (!cg) {
-		if (strstr(name, "..") || strchr(name, '/'))
-			return;		/* illegal */
-		if (cgroups_num + 1 == NELEMS(cgroups))
-			return;		/* exhausted */
+	if (strstr(name, "..") || strchr(name, '/'))
+		return;		/* illegal */
 
-		cg = &cgroups[cgroups_num++];
-		strlcpy(cg->name, name, sizeof(cg->name));
-	}
-
-	cg->cfg[0] = 0;
+	config[0] = 0;
 	while ((ptr = strtok(NULL, " \t"))) {
-		if (cg->cfg[0])
-			strlcat(cg->cfg, ",", sizeof(cg->cfg));
-		strlcat(cg->cfg, ptr, sizeof(cg->cfg));
+		if (config[0])
+			strlcat(config, ",", sizeof(config));
+		strlcat(config, ptr, sizeof(config));
 	}
 
-	_d("cg->cfg: %s", cg->cfg);
+	cgroup_add(name, config, 0);
 }
 
 static void parse_static(char *line, int is_rcsd)
@@ -702,6 +662,7 @@ int conf_reload(void)
 	   daylight, timezone, tzname[0], tzname[1]);
 
 	/* Mark and sweep */
+	cgroup_mark_all();
 	svc_mark_dynamic();
 	tty_mark();
 
@@ -710,9 +671,6 @@ int conf_reload(void)
 	 */
 	memcpy(global_rlimit, initial_rlimit, sizeof(global_rlimit));
 
-	/* Initialize default cgroups */
-	init_cgroups();
-
 	if (rescue) {
 		int rc;
 		char line[80] = "tty [12345] @console noclear nologin";
@@ -784,8 +742,11 @@ int conf_reload(void)
 	service_update_rdeps();
 
 	/* Set up top-level cgroups */
-	cgroup_config(cgroups_num, cgroups);
+	cgroup_config();
 done:
+	/* Remove all unused top-level cgroups */
+	cgroup_cleanup();
+
 	/* Drop record of all .conf changes */
 	drop_changes();
 
@@ -997,9 +958,6 @@ int conf_init(uev_ctx_t *ctx)
 	/* Initialize global rlimits, e.g. for built-in services */
 	memcpy(global_rlimit, initial_rlimit, sizeof(global_rlimit));
 
-	/* Initialize default cgroups */
-	init_cgroups();
-
 	/* Read global rlimits and global cgroup setup from /etc/finit.conf */
 	parse_conf(FINIT_CONF, 0);
 

src/conf.h

@@ -31,15 +31,11 @@ extern int logfile_size_max;
 extern int logfile_count_max;
 
 extern struct rlimit global_rlimit[];
-extern struct cgroup cgroups[];
-extern size_t cgroup_num;
 extern char cgroup_current[];
 
 int   str2rlim(char *str);
 char *rlim2str(int rlim);
 
-struct cgroup *conf_cgfind(char *name);
-
 int  conf_init            (uev_ctx_t *ctx);
 void conf_reload          (void);
 int  conf_any_change      (void);